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Nickel substituted Sr–Co nano spinel ferrites with composition Sr 0.5-x Ni x Co 0.5 Fe 2 O 4 (0.0, 0.1, 0.2, and 0.3) were prepared with the help of a sol-gel auto combustion route. The prepared materials were sintered at 800 for four and a half hours. Analysis of XRD confirmed that the material is composed of a cubic spinel structure with a single phase, and its space group is Fd-3m. Rietveld refinement of X-ray diffraction data was done for all prepared compositions using FULLPROF software. As the composition under study contains more nickel than lattice constant, crystalline size, X-ray density, and bulk density decrease. The dielectric properties were observed about frequency. The dielectric properties revealed that dielectric loss, dielectric constant, and ac conductivity decrease with increasing the Ni2+ content. The activation energy (ΔE) was calculated from the slope of Arrhenius plots. The ΔE found in the range of 0.580–0.096 eV. The analysis of XPS was carried out to examine the elemental state of annealed samples. The prepared material is suitable for employment in applications involving high frequencies because the Ni-doped Sr–Co ferrites with the greatest Ni2+ concentration have the lowest dielectric loss, dielectric constant, and tangent loss value. [ABSTRACT FROM AUTHOR]

Y-type hexaferrite ceramic materials of nominal composition Ba 2 Co 2 Cr x Y x Fe 12-2x O 22 (x = 0.00, 0.03, 0.06, 0.09, and 0.12) were synthesized by sol-gel auto combustion route. Y-type hexaferrites are technologically important ceramic materials for fabricating modern electronic devices and microwave absorbers due to their unique electrical and dielectric properties and reflection loss behavior. XRD classifies the single-phase formations with space group R 3 ‾ m. The crystallite size of the synthesized samples was calculated in (34–41) nm range. The specific absorption band in FTIR spectra approves the (Fe–O) stretching vibrations at wavenumbers 446 and 478 cm−1. The substitution of iron by Cr3+ and Y3+ increases DC resistivity from 1.03 × 1011 to 1.17 × 1012 Ω cm by limiting the electrons jumping between ferrous and ferric ions. The activation energy and drift mobility were also calculated among the substituting content of Cr3+-Y3+. The dielectric response in 1 MHz–6 GHz frequency was determined and the effect of substitution has been observed. The Maxwell-Wagner (MW) bilayer model is used to study dispersion in dielectric parameters with reference to applied frequency. The maximum values of dielectric losses were obtained at 6 GHz in the range of 0.37–0.60. The coercivity values confirms the soft magnetic nature of synthesized samples. The microwave absorption (MW) properties of synthesized materials were improved upon Cr3+-Y3+ substitution. Minimum reflection loss R Lmin = −66 dB (99.99% absorption of MW) at 1.46 GHz frequency and 1.96 mm thickness was obtained for x = 0.09 composition. All investigated samples are efficient materials for stealth technology, radar cross-reduction, EM interference shielding, and high-frequency applications. [ABSTRACT FROM AUTHOR]

The impact of Cr3+ substitution on the electrical and dielectric properties of Y-type hexaferrites with composition Ba 2 Mg 2 Cr x Fe 12-x O 22 (x = 0.0, 0.5, 1.0, 1.5, and 2.0) was synthesized by the sol-gel auto combustion technique. The lattice parameters 'a' and 'c' slightly increase with the substitution content of Cr3+, and some other physical parameters, including porosity, microstrain, dislocation density, specific surface area, and stacking fault coefficient, were determined from XRD data. FTIR spectra confirm the formation of iron oxide base material by the appearance of three signature bands at precisely 429, 474, and 499 cm-1 due to Fe–O vibrations at octahedral and tetrahedral sites. Substituting Cr3+ at the octahedral site enhanced the room temperature DC electrical resistivity from 6.89 × 109 to 2.27 × 1010 Ω-cm. Temperature-dependent DC electrical resistivity exhibits semiconducting behavior. There is a direct relation between resistivity and activation energy. The dielectric behavior of Cr3+ substituted samples in the frequency range of 1 MHz–6 GHz was understood based on the conduction mechanism through the hopping of electrons between Fe3+ and Fe2+ ions and the Maxwell-Wagner Model. In impedance spectroscopy studied using Cole-Cole plots, most dielectric response arises from the contribution of the grain boundary effect. With the substitution of Cr3+, dielectric losses decreased. A very high Q-value around 1 GHz was observed, suggesting that these hexaferrites are efficient materials for many high-frequency applications, such as multi-layer chip inductors (MLCI), dielectric resonators, and power applications. [ABSTRACT FROM AUTHOR]

Polycrystalline Cr3+ substituted Ba 4 Zn 2 Fe 36-x Cr x O 60 (Zn 2 U) U-type hexaferrite compositions Ba 4 Zn 2 Fe 36-x Cr x O 60 (x = 0.0, 0.5, 1.0, 1.5, and 2.0) were fabricated using the sol-gel self-ignition technique. U-type hexaferrite structure was achieved by sintering the powdered samples for 6 h at 1200 °C in a muffle furnace. The phase identification and structural parameters of Zn 2 U hexaferrites were evaluated by X-ray diffraction peaks of the powdered samples. Lattice parameters (a,c) and unit cell volume decreased upon Cr3+ substitution. The crystallite size was measured between 61 and 57 nm. FTIR spectra revealed the existence of specific absorption (Fe–O) bands at wavenumbers 419 and 539 cm−1. These bands further verify the formation of U-type hexaferrite. SEM micrographs showed the platelet-like morphology of the grains with proper hexagonal structure. X-ray photoelectron spectroscopy (XPS) results confirmed the existence of all metal ions with their corresponding electronic states. The dielectric response of the fabricated Zn 2 U U-type hexaferrite pellets was investigated at room temperature through a vector network analyzer with a wide frequency band from 1 MHz to 6 GHz. Dielectric constant (εʹ) was increased for the compositions x = 1.0 and 1.5 while dielectric loss (εʺ), tangent loss (tanδ), and ac conductivity (Ϭ ac) were reduced upon Cr3+ substitution. Single semicircles in the impedance Cole-Cole plots revealed that grain boundaries play a vital role in the conduction process of prepared U-type hexaferrites. Microwave absorption (MW) was improved with Cr3+ substitution. The minimum reflection loss (R L) of −53dB (99.99% MW absorption) at frequency 1.3 GHz was obtained for composition x = 0.5. The dielectric analysis (low losses and high Q-values) of the prepared hexaferrites predicts their appropriate use in high-frequency device applications. [ABSTRACT FROM AUTHOR]

Nano-crystalline Gd-substituted X-type hexaferrites with the composition Ba 2 Co 2 Gd x Fe 28-x O 46 (x = 0.00, 0.08, 0.16, 0.24, and 0.32) were synthesized using sol-gel auto-combustion procedure. The establishment of single and pure phases of X-type hexagonal ferrites is verified by X-ray diffraction. The crystallite size ranging from 25 to 31 nm showed the increasing trend with the enhancement of Gd-substitution. The unit cell volume was found in 2502.83–2516.07 Å3. The alteration in lattice parameters and cell volume is due to the difference in ionic radii of the host (Fe) and substituent (Gd) element. FTIR spectra ranging 590-3000 cm−1 revealed the emergence of specific absorption bands verifying the formation of hexagonal ferrites. The behavior of dielectric properties is frequency dependent. The dielectric constant at low frequency for all substitution was high, but over the large frequency values, the dielectric constant was decreased. The dielectric loss factor increases over low frequencies and decreases as frequency rises with a higher concentration level. Higher dielectric parameter values suggest that synthetic material might be good for high-frequency applications and super-capacitors fabrication. The changes in Raman spectra as a function of substitution content are ascribed to the development of strain in the unit cell (x). The XRD investigation well corroborates this conclusion. FESEM images depicted the hexagon shaped particles of the X type hexagonal ferrites. In the PL spectra of synthesized compounds, all emissions invisible (red) zone with PL intensity at 661 nm were observed. [ABSTRACT FROM AUTHOR]

BaMg 2 Tb x Fe 16-x O 27 (x = 0.00, 0.04, 0.08, 0.12 and 0.16) hexaferrites have been synthesized by sol-gel auto combustion method. The synthesized hexaferrites were characterized by structural, spectral, and dielectric properties. As the ionic radii of substituted element Tb3+(0.93 Å) is higher than Fe3+ (0.64 Å), the lattice parameter 'a' increase with substitution while the lattice parameter 'c' decreases due to internal stresses and lattice distortion. Crystallite size of Tb3+ substituted W-type hexagonal ferrites are calculated and found in the range of 13.2–14.95 nm. FTIR patterns confirm the presence of Fe–O bands at octahedral and tetrahedral sites. The variations in the band positions were observed with substitutions of Tb3+ content. It is also observed that values of both force constants (K o and K t) increase with the inclusion of Tb3+ ions, showing the strong intermolecular bonding. The different parameters of dielectric characteristics were examined in the frequency range 1 GHz–6 GHz, and these showed variation with Tb3+ incorporation and frequency. Dielectric constant, dielectric loss factor, tan loss, and ac conductivity showed an increasing trend while Z′ and Z″ decreases with frequency because conductivity increased. Q value of these materials is low, which may be used in resonant frequency ferrites bead. The obtained results of all parameters including large value of dielectric parameters suggested that these prepared hexaferrites can be used in microwave frequency attenuating devices at GHz, recording, and storage media, and electrical components in mobile phones and refrigerator magnets. [ABSTRACT FROM AUTHOR]

Ba 0.6 Sr 0.4-x Yb x Fe 12-y Co y O 19 , (0.0≤x ≤ 0.125, 0.0≤y ≤ 1.25) M-type hexaferrite were synthesized using the auto combustion sol-gel process. The synthesized samples were then sintered at 1200 °C for 5 h in a muffle furnace. XRD, FTIR, Raman, and Photoluminescence spectroscopies were used to analyse all the samples. XRD technique was used for structural examination of Ba 0.6 Sr 0.4-x Yb x Fe 12-y Co y O 19. The XRD patterns of Yb–Co co-substituted M-type hexaferrites revealed the pure single phase of synthesized samples. Change in Yb–Co concentration influenced lattice parameters and unit cell volume. The variations in lattice constants "a" and "c" values are 5.891–5.862 and 23.180–23.317. FTIR spectroscopic data graphs revealed the formation of several absorption bands from 430 cm−1 to 3000 cm−1. The strain in the unit cell produced by substitution changes in Raman spectra which is also confirmed by XRD. Many 630 nm–700 nm emissions were observed in the PL spectra of Ba 0.6 Sr 0.4-x Yb x Fe 12-y Co y O 19. Furthermore, a bandgap of 1.961–1.875 eV was observed for the pure sample. The substitution improves the dielectric losses and Ac conductivity. The Maxwell-Wagner theory was used to investigate the changing trends of characteristics regarding dielectric parameters. The findings show that the samples with the appropriate cationic substitution can be used in microwave and high-frequency applications. [ABSTRACT FROM AUTHOR]

A series of (Zr–Co) substituted Y-type polycrystalline hexaferrite with composition SrBaNi 2 (ZrCo) x Fe 12-2x O 22 (x = 0.0, 0.25, 0.50, 0.75, 1.0) were fabricated by sol-gel auto combustion method. Pure Y-type single phase formation was achieved at a relatively lower temperature of 1150 °C for 5:30 h. The fabricated nano ferrites were examined by X-ray powder diffraction to confirm the pure single-phase formation of Y-type hexaferrites. An increase in lattice parameters (a& c) was observed by adding Zr4+-Co2+ metal cations. Crystallite size (D) measured in the 48-19 nm range. FTIR spectra clarified iron-oxygen vibrational bands at 417-487 cm−1, which approved the Y-type hexaferrites formation. DC electrical resistivity has an opposite trend at high and low temperatures with increasing Zr4+-Co2+ content (x). DC electrical resistivity values depend on grain size; they have an inverse relation. Activation energy, drift mobility, and Curie temperature were also determined. Conduction is due to the hopping of electrons below the Curie temperature, and polarons are responsible for hopping above the Curie temperature. Activation energy varies from 0.39 to 0.10 eV with the substitution of Zr4+-Co2+ ions. A wide frequency range of dielectric characteristics (1 MHz–6GHz) was observed, and these parameters revealed a considerable fluctuation with the substitution of Zr4+–Co2+ ions. Dielectric constant, dielectric loss and ac conductivity of nano ferrites materials increased with frequency and Zr4+-Co2+ content (x). Complex impedance spectroscopy formalism using the Cole-Cole plots indicated that most dielectric responses arise from grain boundary contributions. [ABSTRACT FROM AUTHOR]

The structural and dielectric properties of Gadolinium substituted U-type hexaferrites (Sr 4 Zn 2 Fe 36 O60) were investigated. The samples were synthesized via the Sol-gel auto combustion route. In a muffle furnace, these samples were sintered for 5 h at 1250 °C. The pellets of synthesized powder samples were characterized by XRD, PL, Dielectric, FTIR, and Raman spectroscopies. Structural elucidation of Sr 4 Zn 2 Fe 36-x Gd x O 60 was done via XRD. The obtained XRD patterns were matched with the prior literature. The impact of Gd3+ substitutions was measured on all the lattice parameters. Lattice constants "a" and "c" were found between 5.871 and 5.900 Å and 111.76–112.23 Å, respectively. The PL spectra of Sr 4 Zn 2 Fe 36-x Gd x O 60 demonstrated multiple emissions in the range of 630 nm–700 nm, and by analyzing PL spectroscopic results, a bandgap of 1.8742 eV was found for the un-doped sample. Many dielectric parameters, i.e., Dielectric constant (ε'), Dielectric losses (ε''), Loss tangents (tanδ), Complex electric modulus (M' & M″), and A.C conductivity (σ ac) were investigated at room temperature by changing the frequencies from 1 GHz to 6 GHz. The varying trends of dielectric parameters were analyzed with the assistance of the Maxwell-Wagner model. Various absorption bands were observed in the range of 500–4000 cm−1 by plotting the FTIR spectroscopic results of Sr 4 Zn 2 Fe 36-x Gd x O 60. Raman spectra demonstrated a combination of strong and fragile peaks in 1–1800 cm−1. The obtained results of various spectroscopies suggested that the prepared materials can be used extensively for different Micro-Wave attenuation purposes. [ABSTRACT FROM AUTHOR]

Nano-crystalline Gd–Co substituted X-type hexagonal ferrites having formula SrBaMn 2-x Co x Gd y Fe 28-y O 46 (where x = 0–1, y = −0.1) were synthesized employing sol-gel route. X-ray diffraction technique verified the formation of pure phase X-type ferrites for all samples. Crystallite size was reduced from 27.49 to 24.52 nm with Gd–Co concentration, which is favorable for attaining an appropriate signal-to-noise ratio in electronic devices. Lattice constants (a, c), bulk, and X-ray density slightly increased owing to the large ionic radius and density of Gd3+ ions than Fe3+ ions. Fourier transform infra-red spectroscopy displayed absorption bands in the lower wavenumber range (482-584 cm−1). The higher absorption bands (482-584 cm−1) are due to metal-oxygen vibration octahedral and tetrahedral sites. The influence of Gd–Co on dielectric properties such as dielectric constant, tangent loss, ac conductivity, and Q-value on frequency and composition were investigated in the frequency region of 1 MHz–3 GHz. The incorporation of Gd–Co resulted in the enhancement of dielectric properties of as-prepared X-type materials desired in electromagnetic devices operating at microwave frequencies. Electric modulus analyses indicated the contribution of grain boundary towards resistance. [ABSTRACT FROM AUTHOR]

Small physical voids will reduce the dielectric strength of epoxy resin and seriously threaten electronic devices' reliability. Self-healing is a practical approach to maintain the electrical and mechanical characteristics of epoxy resin. In this research, epoxy resins incorporated with various concentrations of microcapsules were prepared. The microcapsules were treated using a silane coupling agent (KH550) to enhance dispersion. Moreover, the self-healing performance of the epoxy resin incorporated with microcapsules was analysed by FTIR, SEM, AC breakdown strength, tensile strength, dielectric properties and thermal-stimulated current (TSC). The SEM results indicate that the microcapsules/epoxy resin composite has improved self-healing performance compared to pure epoxy resin. DC volume and surface resistivity of epoxy resins altered obviously after incorporation of microcapsules. Furthermore, the AC breakdown strength of epoxy resin doped with 5 wt% microcapsules was found relatively higher than that of pure epoxy resin. The tensile strength of the epoxy with 5 wt% microcapsules increased initially and then decreased gradually with increasing microcapsule content up to 15 wt%. The dielectric constant and dielectric loss of the epoxy resin/microcapsules composites are slightly higher than that of the pure epoxy resin when the content of the microcapsule is 5%, however, with the increase in microcapsule concentration, the dielectric constant and dielectric loss increase due to the weak interaction zone between microcapsules and epoxy resin. The distribution of trap energy and trap density obtained by TSC measurements revealed that 5 wt% have deeper traps and the highest trap energy levels. [ABSTRACT FROM AUTHOR]

In present research six samples of nano X-type hexagonal ferrites with general formula SrBaMg2-xCoxDyyFe28-yO46 (x = 0–1; y = 0–0.1 with step size of 0.2 and 0.02, respectively) were synthesized by sol–gel technique. The temperature required for the phase formation of these materials was estimated using thermogravimetric analysis. X-ray diffraction patterns revealed the pure phase of the prepared materials up to the doping concentration of x = 0.4, y = 0.04 along with the second phase for higher doping concentration. The secondary phase appeared due to the solubility limit of higher ionic radius Dy3+ ions into the hexagonal lattice. The mean crystalline size decreased from 29 to 18 nm while unit cell volume, bulk density, and X-ray density were increased with Dy-Co doping. Hysteresis loops showed that by incorporation of Dy-Co ions the saturation magnetization (Ms) was enhanced from 50 to 60 emu.g−1. Also, coercivity (Hc) varied in the range 1573–3251 Oe, such high values of Ms and Hc propose the utilization of these X-type materials as permanent magnets and perpendicular recording media. The dependence of dielectric parameters (dielectric constant, ac conductivity, Q-value) on frequency (1 MHz–3 GHz) as well as composition was discussed. Inclusion of Dy-Co in X-type lattice modified dielectric parameters i.e. dielectric constant, ac conductivity was increased. Complex modulus studies directed to elucidate Nyquist plots which exhibited a single half-circle for all X-type ferrites, thus depicting Debye sort of behavior. [ABSTRACT FROM AUTHOR]

In this work, Y 1 − x Pr x F e O 3 (0 ≤ x ≤ 0.16) ceramics were fabricated via the auto-combustion sol-gel method. X-ray diffraction (XRD), scanning electron microscopy (SEM) associated with EDS mapping, and Fourier transform infrared spectroscopy (FTIR) were employed for structural and morphology analysis. The substitution of praseodymium (Pr) modified the orthorhombic structure into a hexagonal structure. However, small traces of Fe 2 O 3 and Y 2 O 3 appeared in all samples. The lattice constant 'a' was increased from 3.523 to 5.530 Å upon substitution up-to x = 0.12, afterward this started to decrease from 5.530 to 5.529 Å. Pure orthorhombic YFeO 3 (o-YFeO 3) has cell volume 223.61 (Å3), while the cell volume of Pr substituted hexagonal YFeO 3 (h-YFeO 3) showed a decreasing trend (125.61–125.43 Å). Bulk density was thoroughly decreased from 5.009 to 4.634 (g/cm3) by increasing the Pr concentration. Frequency dependence of the dielectric behavior was investigated at room temperature in a comprehensive frequency range of 1 MHz ~ 3 GHz. SEM results exhibited the average grain size 149.28 nm, 66.78 nm, and 69.36 nm for the samples 0.00, 0.08, and 0.16, respectively. The identification of o-YFeO 3 was confirmed by two main absorption bands ν 1 (449.86 cm-1) and ν 2 (567.12 cm-1) and these bands indicate a clear shift upon the addition of Pr. The force constant of absorption bands at tetrahedral and octahedral sites showed increasing trend and this ranges from 1.633dyn/cm2x105 to 1.912dyn/cm2x105 and 2.818dyn/cm2x105 to 8.832dyn/cm2x105, respectively. The substitution of Pr significantly enhanced the dielectric constant. The shifting of peaks at higher frequencies demonstrates that an increase of dopant concentration resulted in the shifting of peaks that may follow the Maxwell-Wagner-Sillars polarization mechanism. Pr substituted YFeO 3 exhibited microwave frequency response in a range of 1.6 GHz–2.9 GHz which might be suitable for high-frequency applications. [ABSTRACT FROM AUTHOR]

Indium (In) substituted copper ferrites with nominal composition CuIn x Fe 2-x O 4 (where 0.00 ≤ x ≤ 0.32) were prepared via sol gel route. Influence of In3+ on thermal, structural, spectral, magnetic and dielectric properties are elucidated. The complete decomposition and stable phase formation was assessed from thermal gravimetric analysis (TGA) and differential thermal gravimetric analysis (DTA). The structure of copper ferrite is single phase estimated from X-ray diffraction (XRD) analysis. Lattice constant (a) and crystallite size first increased then decreased with the inclusion of In3+ ions. Cell volume, X-ray density and bulk density are improved due to substitution of indium ions. Magnetic studies are carried out by vibrating sample magnetometer (VSM). The various magnetic parameters i.e saturation magnetization (M s), coercivity (H c) and retentivity (M R) are elucidated. The value of M s and H c are reduced with the substitution of In3+ ions. The squareness ratio, anisotropy constant and Bohr's magneton were also decreased as the inclusion of indium concentration. The value of dielectric constant (ε′), dielectric loss (ε") and tan loss were reduced as frequency increased. The surface morphology was studied by SEM (scanning electron microscopy). The small value of dielectric parameters and coercivity of synthesized ferrites suggested that indium substituted copper ferrites might be useful in switching and high frequency applications. [ABSTRACT FROM AUTHOR]

In this reported study, magnesium-substituted cobalt ferrite nanoparticles (Co1−xMgxFe2O4, x = 0.0, 0.20, 0.35, 0.50) have been investigated. The samples were prepared via a wet chemical co-precipitation route and were calcinated at 800 °C for 6 h. The structural, electrical, and dielectric properties of these samples were studied using XRD, SEM, FTIR, impedance analyzer, and LCR meter. The XRD diffractograms established the development of FCC spinel arrangement with decreasing crystallite size from 20 to 30 nm without any additional impurity peak confirming the purity of the samples synthesized. The FTIR spectra established the existence of tetrahedral (A) and octahedral (B) lattice sites in the structural arrangement. The SEM images showed uniform nano-spherical particle formation with minimum porosity. No extra phase or impurity was found, confirming the effectiveness of the co-precipitation route. The dielectric properties of the synthesized samples measured at ambiance temperature against frequency range of 103 Hz to 5 MHz showed massive enhancement of dielectric constant (on the order of 104 at 100 Hz) which was comparable to traditional ceramics (having a dielectric constant in the range of 104–106), which are often rendered suitable for capacitor applications. Furthermore, the low values of dielectric loss tangent at high frequencies verified its potential usage in microwave applications. A significant contribution of both long- and short-range order in hopping as well as an increase in grain boundary density was confirmed by complex electric modulus analysis. The DC electrical resistivity measurement against increasing temperatures was done, showing a typical decreasing trend with increasing temperature, validating the semiconductor nature of synthesized nanoparticles with varying compositions. The drift mobility was further calculated from the DC resistivity data. [ABSTRACT FROM AUTHOR]

Gallium was substituted in Bi0.97K0.9Fe1−xGaxO3 (x = 0.00, 0.04, 0.08, 0.12, and 0.16) and synthesized using a simple citrate sol–gel technique. Structural, magnetic, dielectric, and optical properties were investigated. XRD patterns revealed two intense peaks (110) and (104) merged into a single peak for x = 0.08 and induced structural phase from rhombohedral to orthorhombic symmetry. Cell volume was decreased with the substitution of K-Ga up to x = 0.12. The crystallite size lies in the range of 17.90–45.71 nm. Bulk density was reduced from 2.36 to 2.24 g/cm3 because bigger ionic incorporation resulted in less diffusion at grain boundaries, increasing inner pores. The optical analysis confirmed that the Ga-O bond length was more significant than the Fe–O bond length, and the Fe–O bond length was stretched with Ga incorporation in BKFO. For x = 0.12, dielectric constant and dielectric loss decreased due to the Ga3+ ion's stable ion yield reduction of Fe3+ at octahedral sites. So, the hopping of electrons between Fe3+ and Fe2+ becomes tricky, and electron accumulation occurs at the interface of grain boundaries which hampers and decreases dielectric polarization. These results suggested that synthesized materials may be applicable in dielectric resonators, magnetic field sensors, and magnetoelectric coupling. [ABSTRACT FROM AUTHOR]

In this study, epoxy resins incorporated with nano-alumina (nano-Al 2 O 3) are prepared with different concentrations of 0, 1, 3 and 5 wt%. The obtained epoxy resin/Al 2 O 3 nanocomposites are subsequently fluorinated using F 2 /N 2 mixture (F 2 /N 2 20% v/v) at 0.05 MPa and 40°C. The nano-Al 2 O 3 is treated with silane coupling agent γ-aminopropyltriethoxysilane (KH550) to restrict aggregation. The chemical bonding is examined by Fourier-transform infrared spectroscopy. The cross-section and surface morphological analyses are performed using scanning electron microscopy. In addition, the DC surface resistivity is measured using a resistivity test fixture. The variations in electrical properties induced by fluorination are characterized based on dielectric measurements. The experimental results show that chemical bonds are formed between nano-Al 2 O 3 and the coupling agent (KH550). Moreover, the results confirm that fluorination significantly alters the morphology and chemical structure of the sample surface. Gas-phase fluorination produces shallow traps, which consequently reduce the surface resistivity. The treatment of nano-Al 2 O 3 increases the trap energy level to yield higher surface resistivity. Furthermore, the treated Al 2 O 3 nanoparticles show improved distribution and dispersion in epoxy resin, exhibiting good dielectric performance of the nanocomposite. [ABSTRACT FROM AUTHOR]

In the present study, the impact of holmium (Ho) substitution on structural, spectral, dielectric and magnetic behavior of Li 1.2 Zn 0.4 Ho x Fe 2−x O 4 (0.00 ≤ x ≤ 0.15) ferrites was investigated. The development of spinel phase and structural changes induced by Ho doping were confirmed by X-ray diffraction. The accommodation of Ho ions into spinel lattice was restricted for x ≥ 0.06 as indicated by ortho phase (HoFeO 3 ) traces. The decrease in lattice parameter ( a ) was attributed to the segregation of Ho ions on grain boundaries. FTIR spectra featured two intrinsic vibrational bands v 1 (617 cm −1 ) and v 2 (488 cm −1 ) for x = 0 due to tetrahedral and octahedral vibrations respectively. The compositional dependence of force constants and bond lengths has explained on the basis of cations distribution and oxygen-cation bond distances of respective sites. The addition of Ho ions decreased the saturation magnetization and optimized the coercivity from 59 to 335 Oe, proposing these ferrites for magnetic recording media. Dielectric results for the entire range of frequency (1 MHz to 3 GHz) revealed that ac conductivity increased from 3.5 × 10 5 to 1.8 × 10 6 (Ω-cm) −1 up to x = 0.09 and then it decreased slightly for x = 0.12. The effective contribution of grain-interior mechanism to dielectric behavior was confirmed by complex impedance study. The results of dielectric studies displayed that Ho doped lithium ferrites are suitable low loss potential materials for high frequency based applications. [ABSTRACT FROM AUTHOR]

Indium substituted Cu Ni nanoferrites with nominal compositions Cu 0.5 Ni 0.5 In x Fe 2-x O 4 (x = 0.00–0.32) were successfully synthesized by sol-gel auto ignition method. X-ray diffraction patterns illustrated the single phase spinel structure for x ≤ 0.24. The lattice parameter 'a' increased from 8.3349 to 8.3723 Å and then it decreased for x = 0.32. X-ray density increased from 5.43 to 5.79 g/cm3. The average crystallite sizes lie in the range 33.21–17.78 nm. The cell volume was increased from 579.03 to 586.86 Å3 with the substitution of indium ions into the spinel lattice of copper nickel ferrites. The compositional dependence of tetrahedral and octahedral radii was explained on the basis of lattice parameter. The incorporation of In3+ ions in copper nickel ferrites exhibited the decreased in bulk density. The dielectric parameters were explained over entire range of frequency (1M-3 GHz). The dielectric parameters i.e dielectric constant, dielectric loss and tan loss were found to decrease with the increase of indium concentration. The saturation magnetization (M s) and Bohr magneton (n B) first increased and then decreased. The remanence (M R) was increased with the substitution of indium ions. The coercivity and anisotropy constant were decreased which might be due to weak A-B super exchange interaction. The results of magnetic and dielectric properties suggested that In3+ substituted copper nickel ferries are suitable for high frequency applications. [ABSTRACT FROM AUTHOR]

Abstract Dysprosium (Dy) doped Y-type strontium hexa ferrites of the following composition Ni 2 Sr 2 Dy x Fe 12-x O 22 where (x = 0.00, 0.05, 0.10, 0.15, 0.20, 0.25) were prepared through co-precipitation process. Phase analysis of the investigated samples was carried out by characterizing through (XRD) X-ray diffraction which confirmed the pure phase of Y-type hexaferrites. Dysprosium ion doping influenced lattice parameters i.e. lattice constants (a, c), crystallite size, (c/a) ratio, cell volume and porosity. The calculated crystallite size was in the range of 88–159 nm. FTIR plots showed that the characteristics bonds of Ni 2 Sr 2 Dy x Fe 12-x O 22 are appreciably influenced by the incorporation of Dy contents. The results of dielectric parameters revealed that dielectric constant, dielectric loss, tanloss were decreased with an increase in frequency. At 6.0 × 108 Hz, dielectric constant decreased from 5.55 to 3.69 with increasing Dy concentration. Owing to Maxwell-wagner type relaxation, the decrease in dielectric constant was noticed at higher frequency. The smaller dielectric constants and dielectric losses make these materials suitable for their applications in microwave devices fabrication. [ABSTRACT FROM AUTHOR]

Abstract A series of BiFe 1-x Hf (3/4)x O 3 (0%, 5%, 10%, 15% and 20%) nanoparticles were synthesized by simple auto combustion technique using citric acid as a fuel. Thermogravimetric (TGA), differential thermogravimetric (DTA), structural, magnetic, dielectric and ferroelectric analyses were investigated. Thermogravimetric analysis provides information of temperature at which phase develops (600 °C). DTA predicts ferroelectric to paraelectric transformation temperature which is found to be 822 °C. X-ray diffraction (XRD) results confirm formation of distorted rhombohedral structure for all compositions along with few traces of Bi 25 FeO 40. The tolerance factor is increased from 0.845 to 0.853 due to larger ionic radius of Hf4+ substitution on Fe site. Crystallite size (D) is found in the range of 24.2–30.48 nm. Saturation magnetization (Ms) is increased to 16 times and remanent magnetization (Mr) is increased to 8 times than that of pure BiFeO 3. This increment in magnetic parameters is due to reduction of oxygen vacancies, small crystalline size (less than 62 nm), structural distortion and unbalancing condition for antiferromagnetic magnetic moments of Fe3+ ions. Dielectric parameters depict decrement behavior with increasing of applied field up to 3 GHz. For Fe 1-x Hf (3/4)x O 3 , lower value of dielectric permittivity for all compositions is due to reduction of polarization and less growth of grains but more growth of grain boundaries because of mismatching of Hf and Fe3+ ions. P-E hysteresis loop changes from round shape to elliptical shape and it confirms less lossy nature of ferroelectric loops. Higher values of Ms as well as Mr but lower values of dielectric constant as well as remanent polarization for these nanoparticles make them useful for MeRAM (magnetoelectric random access memory) and high resonant applications. [ABSTRACT FROM AUTHOR]

In this study, zinc-oxide (ZnO) nanoparticles (NPs) doped with cobalt (Co) were synthesized using a simple coprecipitation technique. The concentration of Co was varied to investigate its effect on the structural, morphological, optical, and dielectric properties of the NPs. X-ray diffraction (XRD) analysis confirmed the hexagonal wurtzite structure of both undoped and Co-doped ZnO-NPs. Scanning electron microscopy (SEM) was used to examine the morphology of the synthesized NPs, while energy-dispersive X-ray spectroscopy (EDX) was used to verify their purity. The band gap of the NPs was evaluated using UV-visible spectroscopy, which revealed a decrease in the energy gap as the concentration of Co2+ increased in the ZnO matrix. The dielectric constants and AC conductivity of the NPs were measured using an LCR meter. The dielectric constant of the Co-doped ZnO-NPs continuously increased from 4.0 × 10−9 to 2.25 × 10−8, while the dielectric loss decreased from 4.0 × 10−8 to 1.7 × 10−7 as the Co content increased from 0.01 to 0.07%. The a.c. conductivity also increased with increasing applied frequency. The findings suggest that the synthesized Co-doped ZnO-NPs possess enhanced dielectric properties and reduced energy gap, making them promising candidates for low-frequency devices such as UV photodetectors, optoelectronics, and spintronics applications. The use of a cost-effective and scalable synthesis method, coupled with detailed material characterization, makes this work significant in the field of nanomaterials and device engineering. [ABSTRACT FROM AUTHOR]

Structural, optical, dielectric, and magnetic characteristics of Sr–Ni–W hexaferrites were probed to justify their potential use in various applications. Sr 1-x Co x Zn y Ni 2-y Fe 16 O 27 (WHFs) ferrites were synthesized by the self-combustible sol-gel method. XRD analysis confirmed a single-phase material with different Co–Zn contents. Fourier transform infrared spectroscopic (400-4000 cm−1) analysis was performed. Variations in Raman intensities indicated the induction of local strain due to a mismatch of ionic radii. The energy band gap (1.879 eV) was calculated from photoluminescence spectra, indicating the semiconducting nature of materials. SEM images showed the presence of grains with hexagonal platelet morphology oriented irregularly, which is highly beneficial for microwave absorption. The high coercivity values indicated that the materials are magnetically hard. Magnetic analysis revealed the potential use of materials in high-storage applications. Dielectric properties were determined using a vector network analyzer within a frequency span (0–6 GHz), indicating materials' usefulness in constructing resonant circuits and MLCIs. [ABSTRACT FROM AUTHOR]

Ba 2−x Cu x Co 2 Cr y Fe 28−y O 46 (x = 0.0, 0.1, 0.2, 0.3, 0.4, y = 0.0, 0.2, 0.4, 0.6, 0.8) X-type hexagonal ferrites were synthesized via micro-emulsion route. The techniques which were applied to characterize the prepared samples are as follows: X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Dielectric measurements and vibrating sample magnetometer (VSM). The structural parameters i.e. lattice constant (a, c), cell volume (V), X-ray density, bulk density and crystallite size of all the prepared samples were obtained using XRD analysis. The lattice parameters ‘a’ and ‘c’ increase from 5.875 Å to 5.934 Å and 83.367 Å to 83.990 Å respectively. The crystallite size of investigated samples lies in the range of 28–32 nm. The magnetic properties of all samples have been calculated by vibrating sample magnetometer (VSM) analysis. The increase in coercivity (H c ) was observed with the increase of doping contents. It was observed that the coercivity (H c ) of all prepared samples is inversely related to the crystalline size which reflects that all materials are super-paramagnetic. The dielectric parameters i.e. dielectric constant, dielectric loss, tangent loss etc were obtained in the frequency range of 1 MHz–3 GHz and followed the Maxwell-Wagner’s model. The significant variation the dielectric parameters are observed with increasing frequency. The maximum Q value is obtained at ∼2 GHz due to which these materials are used for high frequency multilayer chip inductors. [ABSTRACT FROM AUTHOR]

Herein, a SnO 2 /MWCNTs/PANI nanocomposite was synthesized using a wet chemical approach which acts as a multifunctional electrode for supercapacitor and hydrogen evolution reaction. The dielectric properties were studied using the Maxwell-Wagner model of space charge polarization. The increasing dielectric constant indicated the suitability of synthesized NPs for telecommunication, electronics, and other high-frequency applications. The dependence of impedance and dielectric behavior on grains and grain boundaries was further investigated via impedance spectroscopy and complex electric modulus. Based on a 6 M KOH aqueous electrolyte, the SnO 2 /MWCNTs/PANI as an electrode material for supercapacitors displays a capacity of 211 C g−1 at 1 A g−1 and exhibits excellent cycling stability with a capacitance retention ratio of 98% after 5000 cycles at a current density of 2 A g−1. For hydrogen evolution reaction in 0.5 M KOH, SnO 2 /MWCNTs/PANI electrode achieves a benchmark of 10 mA cm−2 at overpotentials of 524 mV. The results reveal that the SnO 2 /MWCNTs/PANI nanocomposite act as multifunctional material that can be used for both energy storage and conversion. [Display omitted] [ABSTRACT FROM AUTHOR]

Ytterbium (Yb) doped X-type hexagonal nano-sized ferrites (Sr 2 NiCoFe 28 O 46 ) were fabricated by micro-emulsion method. The development of hexagonal structure of ferrite materials was confirmed by XRD analysis. The size of crystallites as determined by Scherrer's formula was found in the range 29–41 nm. The lattice strain of these ferrites was increased from 3.62 × 10 −2 to 3.73 × 10 −2 with the increased Yb-contents. The tetrahedral absorption bands shifted slightly towards higher frequency whereas octahedral bands shifted towards lower frequency side. The incorporation of Yb enhanced dc electrical resistivity significantly from 2.05 × 10 8 to 3.35 × 10 9 Ω-cm. The AC conductivity was increased with frequency whereas it decreased with the inclusion of Yb 3+ ions. This distinctive behavior of these hexagonal ferrites may be suitable for microwave devices and electromagnetic attenuation applications. The doping of Yb 3+ optimized coercivity whereas remanence and saturation magnetization were decreased. These ferrite materials can be used in longitudinal recording media due to more thermally stable and higher coercivity (577–671 Oe). [ABSTRACT FROM AUTHOR]

Nano-sized Zr-Co doped nickel ferrites with nominal composition, NiZr x Co x Fe 2-2x O 4 ( x =0.0, 0.2, 0.4, 0.6, 0.8) were synthesized using the micro-emulsion route. The structural elucidation of the synthesized materials was carried out by X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy. The XRD analysis confirmed face centered cubic (FCC) structure of all compositions of NiZr x Co x Fe 2-2x O 4 nanocrystallites. Crystallite size was calculated by Scherrer's formula found in the range 10–15 nm. The variation in lattice parameter as determined by XRD data agreed with size variation of host (Fe 3+ ) and guest (Zr 4+ and Co 2+ ) cations. FTIR spectra of doped NiFe 2 O 4 exhibited the typical octahedral bands at 528.4 cm −1 which is the characteristic feature of spinel structure of spinel ferrites. The characterized spinel NiZr x Co x Fe 2-2x O 4 nano-ferrites were evaluated for their potential applications by magnetic hysteresis loops and dielectric measurements. The value of saturation magnetization ( M s ) decreased from 47.9 to 13.09 emu/g up to x =0.8 with ups and downs fluctuations in between x=0.0 to x=0.8. The high values of Ms of some compositions predicted the potential applications in high density perpendicular recording media and microwave devices. The frequency dependent behavior of permittivity (ε') is recorded and discussed with the help of hopping mechanism of both holes and electrons. The dielectric and magnetic data of NiZr x Co x Fe 2-2x O 4 nano-ferrites suggested the potential applications of these ferrite nanoparticles in high frequency and magnetic data storage devices fabrication. [ABSTRACT FROM AUTHOR]

A series of Dy-doped Li–Ni ferrites of the following composition Li 0.5 Ni 0.48 Tb 0.02 Dy x Fe 2−x O 4 (0.2≤x≥0) was synthesized by the microemulsion method. The X-ray diffraction (XRD) analysis indicated that Li 0.5 Ni 0.48 Tb 0.02 Dy x Fe 2−x O 4 nano-crystalline ferrites exhibited the single-phase spinel structure. The lattice parameter was determined by the Nelson-Riley refinement technique and it increased by increasing the Dy contents. The crystallite size was computed from the Debye Scherrer's formula and it was in range from 27 to 40 nm. The thermal decomposition process was studied by the thermogravimetric analysis and the annealing temperature observed was 980 °C. The real and complex parts of dielectric constant decreases very sharply in the lower frequency region, but in the higher frequency region, the real and complex part of dielectric constant show variable values with Dy contents. The dielectric tangent loss (tan δ) decreases exponentially with Dy contents. The magnitude of the ac conductivity decreases in certain frequency region, as the Dy contents are increased. The possible mechanisms contributing to the above behavior are discussed. The results of these nanocrystalline ferrites are very suitable materials for microwave device applications. [ABSTRACT FROM AUTHOR]

New X-type hexagonal Yb 3+ -doped Ba 2 Co 2 Fe 28 O 46 ferrites were prepared via wet chemical route. The Yb 3+ -contents in Ba 2 Co 2 Yb x Fe 28−x O 46 were kept from 0.00 mol to 0.15 mol in six different compositions. XRD patterns in two theta range 15–70 confirmed the X-type hexagonal ferrites with crystallite size <40 nm. Predicted appropriate variations in lattice parameters and cell volume confirmed the successful substitution of Fe 3+ ions with Yb +3 ions at octahedral sites. The bulk density (D b ), X-ray density (D x ) and porosity (P) were also significantly varied by increased Yb 3+ contents. The fourier transform infrared (FTIR) spectra exhibited the metal-oxygen (Fe-O) stretching vibrational band which further confirmed the successful preparation of hexagonal ferrites. The FTIR band at wave number 1029 cm −1 indicated the presence of cobalt in the pure and un-doped sample which is the characteristic feature of cobalt ferrite. The magnetic measurements carried out in the range −10000 to 10,000 oersted (Oe) at room temperature indicated the increased coercivity (H c ) from 236.4 to 532.7 Oe by increased Yb 3+ contents. However the saturation magnetization (M s ) was decreased from 27.4 to 8.6 emu/g) and retentivity (M r ) decreased from 5.2 to 3 emu/g. The decreased Ms and Mr values are attributed to the modified cationic distribution and re-distribution of cations. The squareness values < 0.5 suggested the multi-magnetic domain structure. The dielectric parameters i.e. dielectric constant, dielectric loss and tangent loss were measured in the frequency range of 1 × 10 6 to 3 × 10 9 Hz and these parameters showed appropriable variations in high frequency region. The optimized dielectric parameters suggested that these prepared hexagonal ferrites can be used in the fabrication of multilayer chip inductors (MLCI's) circuits. [ABSTRACT FROM AUTHOR]

Nanohybrids of CoFe 2 O 4 /MWCNTs with increasing MWCNTs loading from 0.0%, 0.5%, 1%, 1.5%, 2% and 5% by weight were prepared by a novel method of dispersion using ortho-xylene as a dispersive medium for the first time. In our current research, nanoparticles of cobalt ferrite were synthesized via wet chemical co-precipitation route. Non-magnetic MWCNTs matrix was dispersed uniformly in the synthesized ferrite nanoparticles using ortho-xylene as a polar solvent. and Impedance Analyzer were utilized to effectively investigate the synthesized nanohybrid. The obtained X-Ray Powder Diffraction (XRD) images confirm the pure Face Centered Cubic (FCC) single phase of CoFe 2 O 4 /MWCNTs nanohybrid. The average crystallite size remains within the range of 26±6 nm. Scanning Electron Microscopy (SEM) results showed aggregation of ferrite nanoparticles on MWCNTs. Fourier Transform Infrared Spectroscopy (FTIR) was utilized to study the band positions. The dielectric properties were found to be massively enhanced with increased loadings of MWCNTs. The dielectric constant ( ε / ) was massively enhanced from 45 for pure cobalt ferrites to 4.32×10 12 for 5% MWCNTs loading at 100 Hz. The dielectric and tangent losses also increased from 21 and 0.47 for pure cobalt ferrites to 2.33×10 17 and 5.39×10 4 at 100 Hz for 5% MWCNTs loading respectively indicating that this area of research should further be exploited in the realm of super capacitors applications. [ABSTRACT FROM AUTHOR]

Gadolinium (Gd) and Dysprosium (Dy) co-doped Ni-Co (Ni 0.4 Co 0.6 Fe 2 O 4 ) ferrites were prepared by micro-emulsion route. X-ray diffraction (XRD) analysis indicated the development of cubic spinel structure. The lattice parameter and X-ray density were found to increase from 8.24 to 8.31 Å and 5.57 to 5.91 (gm/cm 3 ) respectively as the Gd-Dy contents increased in nickel-cobalt ferrites. The crystallite size calculated from the Scherrer's formula exhibited the formation of nanocrystalline ferrites (13–26 nm). Two foremost absorption bands observed in FTIR spectra within 400 cm −1 (υ 2 ) to 600 cm −1 (υ 1 ) which correspond to stretching vibrations of tetrahedral and octahedral complexes respectively. The dielectric constant (ε) and dielectric loss (tanδ) were decreased by the optimization of frequency and abrupt decrease in the low frequency region and higher values in the high frequency region were observed. The dielectric dispersion was due to rapid decrease of dielectric constant in the low frequency region. This variation of dielectric dispersion was explicated in the light of space charge polarization model of Maxwell-Wagner. The dielectric loss occurs in these ferrites due to electron hopping and defects in the dipoles. The electron hopping was possible at low frequency range but at higher frequency the dielectric loss was decreased with the decrease of electron hopping. Magnetic properties were observed by measuring M-H loops. Due to low dielectric loss and dielectric constant these materials were appropriate in the fabrication of switching and memory storage devices. [ABSTRACT FROM AUTHOR]

The influence of rare-earth metals (La, Nd, Gd, Tb, Dy) on morphology, Raman, electrical and dielectric properties of Ba 2 NiCoRE x Fe 28− x O 46 ferrites were studied. The scanning electron microscopy (SEM) exhibited the platelet like structure of these hexagonal ferrites. The surface morphology indicated the formation of ferrite grains in the nano-regime scale. The bands obtained at lower wave number may be attributed to the metal-oxygen vibration at octahedral site which confirm the development of hexagonal phase of these ferrites. The resonance peaks were observed in dielectric constant, dielectric loss factor and quality factor versus frequency graphs. These dielectric parameters indicate that these ferrites nano-materials are potential candidates in the high frequency applications. The enhancement in DC electric resistivity from 2.48×10 8 to 1.20×10 9 Ω cm indicates that the prepared materials are beneficial for decreasing the eddy current losses at high frequencies and for the fabrication of multilayer chip inductor (MLCI) devices. [ABSTRACT FROM AUTHOR]

Terbium (Tb) and dysprosium (Dy) doped lithium-nickel nano-sized ferrites (Li 0.2 Ni 0.8 Tb 0.5 x Dy 0.5 x Fe 2− x O 4 where x =0.00−0.08) were prepared by micro-emulsion technique. The X-ray diffraction (XRD) patterns confirmed the single phase cubic spinel structure. The lattice constant was increased due to larger ionic radii of Tb 3+ and Dy 3+ cations. The crystallite size was found in the range 30–42 nm. The FTIR (Fourier transform infrared spectroscopy) spectra revealed two significant absorption bands (~400–600 cm −1 ) which indicate the formation of cubic spinel structure. The peaking behavior of dielectric parameters was observed beyond 1.5 GHz. The dielectric constant and dielectric loss were found to decrease by the increase of Tb–Dy contents and frequency. The doping of Tb and Dy in Li–Ni ferrites led to increase the coercive field (120–156 Oe). The smaller magnetic and dielectric parameters suggested the possible utility of these nano-materials in switching and microwave devices applications. [ABSTRACT FROM AUTHOR]

• Sol-gel route was used to prepare Ba 3 Co 2-x Mg x Fe 24 O 41 hexaferrites. • The occupancy of Mg2+ ions at the octahedral site was altered by Fe3+ ions. • The dielectric permittivity was decreased by incorporating of Magnesium. • Cole – Cole plots revealed a single semi-circle. • Magnetic investigations unfolded ferrimagnetic nature of all samples. The Ba 3 Co 2-x Mg x Fe 24 O 41 hexaferrites were prepared by the sol–gel combustion route. The materials were annealed at 1350 °C and displayed the single-phase characteristics. X-ray density (D x) decreases owing to increasing Mg-concentration. Crystallite size was calculated with the help of Debye Scherrer's formula and found within the 17–18 nm range. Fourier transform infrared spectroscopy was used to determine the specific absorption peaks of hexagonal ferrites. It was executed in the region of 420–700 cm−1—the occupancy of Mg2+ ions at the octahedral site at delayed alternation of Fe3+ ions. As a result, the dielectric permittivity decreased. The grain boundary contribution was clearly seen in synthesized ferrites' cole plots. The cole – cole plots show a single semi-circle which reveals that grain boundaries play a significant role in the conduction process. Magnetic measurement indicated the ferrimagnetic behavior of all samples. [ABSTRACT FROM AUTHOR]

The substitution of Neodymium (Nd) in the cobalt - zinc (Co–Zn) ferrite was analyzed. The sol-gel technique was used to synthesize the se ceramic samples. The crystalline structural, molecular characterizations, and magnetic properties were analyzed by X-ray diffraction (XRD) and Fourier transform infrared (FTIR) experiments, and vibrating sample magnetometer (VSM) respectively. XRD patterns revealed the single-phase cubic spinel structure of the samples. Lattice p arameter varied from 8.41 to 8.38 Å with the inclusion of Nd concentration. The existence of two characteristic frequency bands in the range of 400–1400 cm−1 was confirmed by FTIR spectra. VSM measurements showed the magnetic behaviour at room temperature. The saturation magnetization was noted to decrease from 81 to 66 emu/g with increasing the Nd concentration. The sample having step size x = 0.025 revealed the highest coercivity and retentivity. Dielectric properties were studied and showed variation in dielectric constant, dielectric loss, ac conductivity, and energy dissipation (tangent loss) in the prepared material s. • Auto-citric combustion method was used to prepare Co0·6Zn0.4NdxFe2-xO4 ferrites. • The estimated value of constant lattice decreases upon increasing Nd ions. • Intrinsic vibrational bands revealed a shift with increasing the Nd content. • The porosity of the samples increased from 0.41 to 0.55. • Nd inclusion optimized saturation magnetization and coercivity. [ABSTRACT FROM AUTHOR]

Terbium (Tb) doped X-type hexagonal nano-ferrites Sr 2 NiCoTb x Fe 28− x O 46 ( x =0.00, 0.05, 0.1, 0.15, 0.2) were synthesized via micro-emulsion route. Single phase X-type hexagonal structure was confirmed by X-ray diffraction (XRD) analysis. The crystallite size of the samples was found in the range of 15–25 nm. The bulk density and X-ray density were enhanced while porosity was reduced with the increased Tb 3+ contents. The development of hexagonal phase was investigated by thermogravimetric analysis. The fourier-transform infrared (FTIR) spectra revealed the formation of spectral bands (metal-oxygen stretching vibration) which confirmed the hexagonal ferrites. The dielectric constant has high value at low frequency and decreased with increased frequency. The dielectric loss is appreciably decreased by the Tb 3+ incorporation and resonance phenomenon occurred beyond 1.7×10 9 Hz. The saturation magnetization (76–54 emu/g) and remanance (27–21 emu/g) decreased while coercivity increased (610–747 Oe) by Tb 3+ -incorporation in Sr 2 NiCoTb x Fe 28− x O 46 ferrite. The values of squareness ratio (0.35–0.39) indicated that Tb-doped samples are single domain while un-doped material is multi domains. These synthesized nano-sized hexagonal ferrites have potential applications in high frequency and recording media devices. [ABSTRACT FROM AUTHOR]

In this study, novel three-phase hybrid (inorganic-organic) composite comprising Fe0.01La0.01Al0.5Zn0.98O ceramic particles (FLAZPs), conducting polymer polyaniline (PANI) and grapheme oxide (GO) was synthesized. The ceramic particles were produced by sol-gel technique. For the homogeneous dispersion of FLAZPs particles in the PANI matrix, in-situ free-radical polymerization of aniline (PANI precursor) was performed. FLAZPs distributed in the matrix during the polymerization process. GO was synthesized via modified Hummer's method which was then blended with two-phase composite using simple one-pot blending technique. The prepared materials were subjected to FT-IR, TGA, XRD and SEM to analyze their physical properties. FT-IR showed the successful complexation of the materials with one another. XRD confirmed the crystalline nature and phase distribution in the composites. FLAZPs enhanced the thermal stability of PANI and GO in the composites. SEM showed that ceramic particles are in the range from micro to nanometer and are well dispersed in the PANI matrix in two-phase composite. Furthermore, GO prevented the agglomeration of particles while interacting with PANI in the three-phase composite. Extensive dielectric studies were carried out which showed that PANI and GO have about the same additional effect on various dielectric properties of FLAZPs. The AC conductivity (σ = 7.79 x 10-1 Ω-1cm-1) achieved by two-phase and three-phase composites is much higher in comparison to pure FLAZPs (σ = 3.17 x 10-1 Ω-1cm-1). [ABSTRACT FROM AUTHOR]

Dy 3+ and Fe 3+ co-doped LaCoO 3 perovskite nanoparticles were prepared by chemical co-precipitation route. Structural elucidation was carried out by thermo gravimetric analysis (TGA), X-ray diffraction (XRD), scanning electron microscopy (SEM), and Fourier transform infrared (FTIR) spectroscopy. The data of all these characterization techniques confirmed the orthorhombic phase with particles size in the range of 20–60 nm. The magnetic parameters, DC-resistivity and dielectric properties were measured for La 1− x Dy x Co 1− y Fe y O 3 nanoparticles. The purpose of all these application studies was to evaluate the prepared materials for practical applications. The substitution of Dy 3+ and Fe 3+ with La 3+ and Co 3+ respectively greatly influenced the magnetic, DC-resistivity and dielectric parameters. [ABSTRACT FROM AUTHOR]

• Sol-gel technique was employed to synthesize Ba 4 Cu 2-x Ni x Fe 36 O 60 ferrites. • Cole-Cole plots markedly distinguished grain boundary contribution. • Coercivity (H c) increased (1844.44–2946.83 Oe) by increasing Ni contents. • The squareness ratio (0.471–0.450) revealed single magnetic domain. • The results suggest their potential use in high-frequency applications. This paper reports the impacts of nickel substitution on dielectric, magnetic, and structural characteristics of Ba 4 Cu 2-x Ni x Fe 36 O 60 hexaferrites prepared via the sol–gel method. The sample was annealed for 5 h at 1200 °C. The crystalline structure, magnetic and dielectric features were examined by X-ray diffraction, vibrating sample magnetometer, and impedance analyzer individually. The specific absorption bands of hexagonal ferrites were identified by FTIR spectroscopy and in the 420–600 cm−1 range. M−H loops of samples were determined to examine the magnetic properties of synthesized materials. Magnetic measurement shows that samples exhibit ferrimagnetic behavior at room temperature. The magnetic properties are described in cation distribution and grain size effect. Dielectric properties of the samples were observed in the frequency range (1–3 GHz). Cole-Cole graphs of prepared materials revealed the influence of grain boundaries. A single semi-circle in the impedance Cole-Cole plots approves a special part of grain boundaries in the conduction process. Dielectric properties are affected by the electron hopping mechanism between Fe2+ and Fe3+ ions. These performances expose that these nanomaterials are appropriate for high-frequency applications. [ABSTRACT FROM AUTHOR]

The microstrip patch antenna (MPA) has been in use and has been studied extensively during the past three decades. This antenna, which consists of a metallic patch printed on a dielectric substrate over a ground plane, offers several advantages including ease of design and fabrication; low profile and planar structure; and ease of integration with circuit elements. The minimum dimension of a conventional MPA is in the order of half a wavelength. In recent years, with the advent of new standards and compact wireless devices, there has been a need to reduce the size of this type of antenna. This study discusses some of the principal techniques that have been reported in the literature to reduce the size of an MPA. These miniaturisation techniques include material loading, reshaping the antenna, shorting and folding, introducing slots and defects in the ground plane and the use of metamaterials. The major features and drawbacks of each of these approaches are highlighted in this study along with their effects on the antenna performance metrics. [ABSTRACT FROM AUTHOR]

Polycrystalline ferrites with chemical formula MgY 2 x Fe 2−2 x O 4 ( x =0.0 to 0.12) have been fabricated by a double sintering ceramic technique. The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Impedance spectroscopy and Fourier transform infrared (FTIR) spectroscopy. A slight increase in lattice constant is observed for x =0.02 and thereafter it decreased for higher Y-contents. The increase in lattice constant is attributed to the difference in ionic radii of the cations involved and decrease led to the formation of secondary phase (YFeO 3 ). The substitution of yttrium impedes the grain growth. The resistivity at 298 K was significantly enhanced as the Y 3+ was increased. The FTIR band positions in the range of 370–1100 cm −1 exhibited two main absorption bands. These bands confirmed the completion of solid state reaction. As the Yttrium contents were increased the dielectric parameters were greatly influenced. Both the observed/optimized electrical and dielectric parameters suggested the potential use of the Y-doped MgFe 2 O 4 ferrites in high frequency devices fabrication. [ABSTRACT FROM AUTHOR]

A series of nanocrystalline cobalt ferrites doped with yttrium ions were synthesized by chemical co-precipitation technique. The X-ray diffraction analysis reveals that all the samples exhibit cubic spinel phase as main phase along with few traces of orthorhombic phase (YFeO 3 ). The crystallite size calculated by Scherrer’s formula is found in the range of 48–34 nm. This crystallite size is small enough to obtain the suitable signal to noise ratio in the high density recording media applications. The lattice constant was found to decrease from 8.385 Å to 8.348 Å with the increase of yttrium contents which may be attributed to the solubility limit of yttrium ions. The dc electrical resistivity was found to increases from 4.95×10 6 Ω-cm to 8.39×10 7 Ω-cm with the increase of yttrium contents. Yttrium doped samples exhibit lower dielectric constant and dielectric loss tangent as compared to pure CoFe 2 O 4 nanocrystals. An appreciable increase in coercivity has been observed by the Y 3+ addition. The enhanced dc electrical resistivity and coercivity ( H c =1273 Oe) of cobalt nanoparticles (5 wt% doped Y 3+ ) are favorable for their potential use in microwave devices and high density recording media applications. [ABSTRACT FROM AUTHOR]

Abstract: Tb3+-doped nanocrystalline zinc ferrites with a nominal composition of Zn1−x Tb x Fe2O4 (x=0, 0.03, 0.06, 0.09, 0.12 and 0.15) were prepared by micro-emulsion method and were annealed at 600°C for 8.5h. The synthesized samples were characterized by thermogravimetry analysis (TGA), differential scanning calorimetry (DSC), X-ray powder diffraction (XRD), fourier transform infrared spectroscopy (FTIR), vibrating sample magnetometer (VSM) and dielectric measurement techniques. The powder XRD patterns confirm the single phase cubic spinel structure, indicated that doping nanoferrites with small concentrations of terbium ions allowed their entrance to the spinel lattice and the crystallite size is found in the range of 16–24nm. The dielectric constant (ε) and dielectric loss (tanδ) of all the samples were measured in the frequency range 100MHz–3GHz at room temperature. The dielectric constant and dielectric loss of the samples are found to decrease with increase in frequency and Tb3+ content. The reduction in the dielectric parameters is attributed to the obstruction incorporated in electron exchange mechanism caused by the lockup among iron and terbium cations. The magnetic properties revealed that these terbium doped nanocrystalline zinc ferrites exhibit ferrimagnetic behavior. The high saturation magnetization and coercivity along with smaller dielectric parameters having Tb-contents suggests that the materials are suitable for applications in memory devices and high frequency applications. [Copyright &y& Elsevier]

This work presents a new technique for enhancing the performance of a multiple-input multiple-output (MIMO) antenna by improving its correlation coefficient ρ. A broadband dielectric structure is designed using the transformation electromagnetics (TE) concept to decorrelate the fields of closely placed radiating elements of an MIMO antenna, thereby decreasing ρ and mutual coupling. The desired properties of the broadband dielectric wave tilting structure (DWTS) are determined by using quasi-conformal transformation electromagnetics (QCTE). Next, the permittivity profile of the DWTS is realized by employing air-hole technology, which is based on the effective medium theory, and the DWTS is fabricated using the additive manufacturing (3D printing) technique. The effectiveness of the proposed technique is verified by designing two-element patch-based MIMO antenna prototypes operating at 3 GHz, 5 GHz, and 7 GHz, respectively. The proposed technique helped to reduce the correlation coefficient ρ in the range of 37% to 99% in the respective operating bandwidth of each MIMO antenna, thereby, in each case, improving the isolation between antenna elements by better than 3 dB, which is an excellent performance. [ABSTRACT FROM AUTHOR]

Abstract: The effects of concentration of terbium (Tb) on ferromagnetic resonance (FMR), relative initial permeability, morphology, and dielectric properties of MgFe2O4 ferrites were studied. It is found that FMR line-width and FMR position of magnesium–terbium (Mg–Tb) ferrites are found to fluctuate with the increase of Tb-content. The increase in FMR line-width is attributed to the charge transfer mechanism and inhomogeneity in the samples (TbFeO3). The relative initial permeability decreases gradually as a function of Tb-content. The magnetic loss factors of substituted samples exhibit decreasing behavior in the frequency range 1kHz to 10MHz. Terbium substituted samples have lower dielectric constant as compared to the pure MgFe2O4 ferrite. The decrease in dielectric constant is attributed to the retardation in electron exchange mechanism caused by lockup among iron and terbium ions. An irregular behavior of the dielectric loss is found, which is related to the hopping probability of charges in these ferrites. A decrease in the ac conductivity is observed beyond 8MHz and this corresponds to the occurrence of dielectric loss. The low magnetic and dielectric behavior makes these ferrite materials suitable for their applications in microwave devices. [Copyright &y& Elsevier]

Abstract: With an aim to reveal the mechanism of protein–water interaction in a predominantly two phase model protein system this study investigates the frequency and temperature dependence of dielectric constant ɛ′ and loss factor ɛ″ in cow horn keratin in the frequency range 30Hz to 3MHz and temperature range 30–200°C at two levels of hydration. These two levels of hydration were achieved by exposing the sample to air at 50% relative humidity (RH) at ambient temperature and by evacuating the sample for 72h at 105°C. A low frequency dispersion (LFD) and an intermediate frequency α-dispersion were the two main dielectric responses observed in the air-dried sample. The LFD and the high frequency arm of the α-dispersion followed the same fractional power law of frequency. Within the framework of percolation cluster model these dispersions, respectively have been attributed to percolation of protons between and within the clusters of hydrogen-bonded water molecules bound to polar or ionizable protein components. The α-dispersion peak, which results from intra-cluster charge percolation conformed to Cole–Cole modified Debye equation. Temperature dependence of the dielectric constant in the air-dried sample exhibited peaks at 120 and 155°C which have been identified as temperatures of onset of release of water bound to polar protein components in the amorphous and crystalline regions, respectively. An overall rise in the permittivity was observed above 175°C, which has been identified as the onset of chain melting in the crystalline region of the protein. [Copyright &y& Elsevier]

Hexagonal ferrites have gained much attraction due to extensive applications in telecommunication and stealth fields. R-type hexagonal ferrites are rare hexagonal ferrites used in various technological applications. In the current work, the sol-gel auto-combustion method was used to prepare samples of R-type hexagonal ferrites with the chemical formula BaZr 2 Fe 4-x Pr x O 11 (x = 0.00, 0.03, 0.06, and 0.09) respectively. The impact of substituting Praseodymium (Pr) on its structural, electrical, dielectric, and magnetic properties was investigated. X-ray diffraction (XRD) patterns suggest all samples exhibit a single phase. The lattice parameters and unit cell volume experienced alterations with varying Praseodymium (Pr3+) substitution levels. The atomic dynamics study of the Pr-doped R-type hexagonal ferrites was evaluated using FTIR analysis. Two absorption bands in the infrared spectroscopy were utilized to designate the tetrahedral and octahedral sites. X-ray photoelectron spectroscopy (XPS) findings verified the presence of all metal ions alongside their respective electronic states. Jonscher's power law elucidates the conduction mechanism of charge carriers in the synthesized ferrite samples. Impedance analysis was employed to investigate the influence of relaxation time and grain boundaries on the electrical characteristics of the fabricated nanomaterials. Impedance Cole-Cole plots provide evidence that all samples demonstrate multiple relaxation processes of a non-Debye nature. The minimum reflection loss (RL) of −32.46 dB at 3.27 GHz was achieved for x = 0.09. Pr-doped R-type hexagonal ferrite has potential applications in microwave high-frequency applications. [ABSTRACT FROM AUTHOR]

Dysprosium (Dy3+) substituted cobalt-zinc spinel ferrites were synthesized having composition (Co0.7Zn0.3 Dy3+ xFe2−xO4) with the concentration ranges from (0.00, 0.5, 0.10, 0.15, and 0.20) by using the Sol–Gel synthesis. XRD analysis confirmed the FCC spinel structure of the prepared samples. Lattice constant and X-ray density were calculated in variance ranging from 8.40–8.46 Å and 5.28–5.77 g/cm3, respectively. Fourier Transformation Infrared Spectroscopy (FTIR) were used to measure the frequency band in between 411–562 cm−1 for the tetra and octahedral positions. Scanning electron microscopy was used to study the surface morphology of the prepared samples. The field emission transmission electron microscopy (FE-TEM) was used for the confirmation of particle size. The calculated value of crystalline size was 13 nm, while particle size was the best on 23 nm. It was observed that, on applied field frequency the dielectric parameters exhibits decreasing trend. Magnetic properties were examined by Vibrating Sample Magnetometer (VSM) method and found out saturation magnetization (63.99 emu/g), anisotropy (K) (5366.82 J/m3) and magnetic moment (2.77) were in decreasing while retentivity (2.38 emu/g), squareness ratio (0.07) and coercivity Hc (133.71Oe) were in increasing trend respectively. These features of Dy3+ substituted Co–Zn spinel ferrites recommend their better use in sensors and high frequency devices. [ABSTRACT FROM AUTHOR]

In the current study, the solid solution of (Ca1 − xBax)4Ti3O10, 0.00 ≤ x ≤ 0.075-sintered ceramics were synthesized through traditional mixed oxide solid state technique. The phase evolution, morphological, vibrational, and microwave dielectric properties of synthesized samples were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), and impedance analyzer (1 MHz–3 GHz). The X-ray diffraction (XRD) profile shows the tetragonal I4/mcm crystal symmetry of the system. The surface morphology showed the existence of spherical and round-like micro-size structures. The stretching vibrational mode of O-H and Ti-O was recorded at 600 cm−1 and normal vibrational mode at 500 cm−1, respectively. Using UV-Vis spectroscopy, the optical band gap energy of (Ca1 − xBax)4Ti3O10-sintered ceramics is found at 1.967, 1.878, 1.749, and 1.613 eV for x = 0.00, 0.025, 0.05, and 0.075, respectively. At Optimum microwave dielectric properties of samples were recorded at 3-GHz frequency. The obtaining results have been suitable for the applications of microwave wireless communication system. [ABSTRACT FROM AUTHOR]

The impact of Ni2+ and Zr4+ on the physical properties of LiFe 2 O 4 ferrites is investigated and synthesized via the microemulsion technique. X-ray diffraction pattern of pure and substituted lithium ferrites exhibited spinel structure. The constant lattice increases with increasing dopants concentration up to x = 0.2 and decreases for higher x. The crystallite size value varies from 8.15 to 12.37 nm. The incorporation of heavier ions with lighter ions increased the X-ray density of lithium ferrites. The value of dielectric parameters such as dielectric constant and dielectric loss decreases with the substation of Ni2+ and Zr4+ ions. The Maxwell Wagner model ascribes the decrease in dielectric parameters. Substituted lithium ferrites observe a high Q value. The magnetic studies revealed that saturation magnetization and coercivity were significantly affected by Ni2+ and Zr4+ ions. The inclusion of Ni2+ and Zr4+ ions improves the dielectric and magnetic properties making it suitable for high-frequency applications. [ABSTRACT FROM AUTHOR]