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Doping of potassium in CaCr2O4 as Ca1−xKxCr2O4 with x = 0.2, 0.4, 0.6, and 0.8, using sol-gel technique, to see the structural changes in a regular and periodic variation of K-ions. XRD pattern shows a reduction in peak intensities of CaCr2O4 after potassium doping, principally owing to bonding with Alkali metal in heat treatment of Ca1−xKxCr2O4. It revealed that active species might be confined in the non-crystalline phase, thus impeding their reactivity. XRD of grown samples show their cell parameters of hexagonal crystal symmetry. Morphology of samples in SEM, exhibited the introduction of potassium into the medium of transition metal oxide effects in the development of channeled or layered assemblies. Constituents of synthesized material [Ca1−xKxCr2O4], presenting vibrational stretching of constituent elements as observed in Raman Spectra. The structure of doped sample is predicted favorable for energy storing devices, as having distortion (amorphous linings) in its crystal structure when compared to un doped one, that evident the novelty of this work. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Ce-substituted NZO samples were synthesized by sol–gel auto combustion method. • A strong coupling between magnetic and dielectric order parameters was observed. • Magnetodielectric response increased with substitution contents. Abstract In this letter, we report the energy storage capacity and magneto-dielectric tenability of rare earth zirconates, by synthesizing a series of Ce-substituted neodymium zirconates having general formula, Nd 2 Zr 2−x Ce x O 7 (x = 0.0, 0.4, 0.8, 1.2, 1.6 and 2.0), using sol–gel auto-combustion method. Linear ferroelectric response and energy storage efficiency was checked from polarization loops. Magnetic characterization revealed that rare earth zirconates had small values of coercivity and remanence which argued mainly a superparamagnetic nature of the samples. Tailoring of dielectric properties with the magnetic field and a possible origin of magneto-dielectric coupling was also investigated. [ABSTRACT FROM AUTHOR]

ZnMnO ( = 0, 0.02, 0.04, 0.06, 0.08 and 0.1) nanocrystalline diluted magnetic semiconductors (DMSs) were synthesized using sol-gel-based auto-combustion technique. X-ray diffraction (XRD) analysis of all the synthesized samples indicated pure wurtzite hexagonal structure without any secondary phase with perfect solubility of Mn contents in ZnO matrix. The increase in Mn concentration reduced the average crystallite size as evaluated by the Scherrer's formula. Morphological analysis performed using a field emission scanning electron microscope (FESEM) indicated nearly an ordered surface morphology with some porosity and few cracks. Energy dispersive X-ray (EDX) spectroscopy confirmed the stoichiometric contents of Zn, Mn and O in each sample. Micrographs of all the samples exhibited a decrease in grain size with increase of Mn contents. Magnetic measurements performed using vibrating sample magnetometer (VSM) confirmed room temperature ferromagnetism exhibiting an increase in saturation magnetization and coercivity with increasing Mn contents in all the prepared samples. [ABSTRACT FROM AUTHOR]

Glycine + urea are used as fuel agents to synthesize polycrystalline nano-particles of as-burnt BiSrFeO and BiSrFeMnO (x = 0, 0.05, 0.10, 0.15 and 0.20) multiferroic samples using sol-gel auto-combustion method, at relatively low temperature. Structural analysis exhibits the formation of phase pure nano-composites having rhombohedral distorted perovskite structure belonging to space group R3c. Doping of Sr and Mn didn't disturb the crystal symmetry of the original composite. Field emission scanning electron microscopy revealed that the grains which were initially interlinked with each other became relatively isolated, uniformly distributed and spherical shaped with increasing Mn contents along with increased intergranular porosity. Energy dispersive X-ray spectroscopy confirms the at.% and wt% of all the elements, corresponding to each stoichiometric formula. Dielectric parameters for each sample depict conventional ferrite behavior while hopping of oxygen vacancies contributes a lot in conductivity of the samples. Contribution of grains, grain boundaries and interfaces are evident from impedance spectroscopy. Non-Debye type relaxation is confirmed from the frequency dependent electric modulus and Cole-Cole plots. A solid correlation has been established between electrical properties and microstructure of the samples under investigation. [ABSTRACT FROM AUTHOR]

In this work, Au/Fe3O4 nanocomposite materials with exact spinel structure were successfully synthesized where impurities-free Fe3O4 was prepared using sol-gel autocombustion method and gold was doped with various concentrations 1, 3, and 5 wt.% using conventional deposition–precipitation method. Methylene blue with fixed concentration (0.05 mM) was used to investigate the photocatalytic activity under visible light. Due to homogeneous and controlled compositions, Au/Fe3O4 nanocomposites showed enhanced photocatalytic efficiency than pure Fe3O4. [ABSTRACT FROM AUTHOR]

We report synthesis of Zn 1−x Mn x Fe 2 O 4 (x = 0.0, 0.1, 0.3, 0.4 & 0.5) ferrites using sol-gel auto-combustion route while citric acid is used as a fuel. The study is aimed to explore the influence of Mn contents on structural parameters, morphological characteristics and magnetic properties of ZnFe 2 O 4 ferrite samples while the impact of average grain dimensions on magnetic properties inferred from multi domain and single domain particle's effect is also analyzed. X-ray diffraction confirmed the configuration of single phase pure crystalline structure with low concentration of Mn while some impurity peaks were found for higher Mn contents. Lattice parameter was found to increase with increasing Mn contents while crystallite size was decreased. Average grain size was decreased from 240 to 150 nm with increasing Mn concentration which directly affected the magnetic properties. A decrease in saturation magnetization (from 52.35 to 45.80 emu/g) and an increase in coercivity (from 44 to 262 Oe) was observed with increasing Mn contents. A decrease in initial permeability and increase in hysteresis loss with increasing Mn contents was also evident. Coercive field and hysteresis losses were increased with decreasing average grain size while initial permeability was found to decrease with decrease in average grain size. [ABSTRACT FROM AUTHOR]

We here report the preparation of undoped BiFeO3 (BFO) thin films with sol-gel method using two solvents, i.e., acetic acid (AA) and ethylene glycol (EG). Films are annealed in the temperature range 100–300 °C for 60 mins. Films deposited using AA show the presence of bismuth rich phase Bi46Fe2O72 along with BFO in the intermediary conditions. Pure phase BFO is obtained when films are deposited using EG as a solvent even under as-deposited conditions, and the pure phase persists after annealing in the temperature range 100 °C–300 °C. This is the lowest temperature reported for the preparation of phase pure BFO. Bandgap of AA-based films lies in the range 2.58–2.64 eV and that of EG-based films in the range 2.77–2.81 eV. Reduced value of dielectric constant, in AA-based films, is because of the presence of bismuth rich impurity phase as compared with the films prepared using EG. Bands in FTIR spectra at 487 and 552 cm \(^{-1}\) are characteristic bands of FeO6 and BiO6 groups, indicating the formation of BFO. Films deposited using AA show weak ferromagnetic behavior, while those deposited using EG show strong ferromagnetic behavior as opposed to antiferromagnetic nature of BFO, due to suppression of spiral spin structure. [ABSTRACT FROM PUBLISHER]

Manganese copper ferrites belong to a family of ferrites with specific importance due to their high permeability values and low losses at low frequencies. In this paper, a series of ferrite samples has been synthesized using a novel and low cost sol-gel autocombustion route in order to systematically investigate the structural, compositional, morphological, and magnetic properties when zinc is substituted by copper in the series. X-ray diffraction reveals that all the samples have characteristic cubic spinel structure. The effect of zinc substitution at the copper site on the chemical bonding of the ferrite samples was investigated by Fourier transform infrared spectroscopy. Energy dispersive X-ray analysis was performed to determine the homogeneity and stoichiometric composition of elements present in the samples. Nanosized, uniformly shaped grains were evident from the images obtained using a scanning electron microscopy, which indirectly confirms the significance of the autocombustion synthesis technique employed in this paper. Magnetic properties determined using a vibrating sample magnetometer exhibited that zinc substitution could enhance the saturation magnetization of the samples, attributed to the substitution of a paramagnetic element (zinc) by a diamagnetic one (copper). [ABSTRACT FROM PUBLISHER]

Bismuth iron oxide (Bi1−xKxFeO3) thin films are prepared using sol-gel and the spin coating method. Films are deposited onto copper substrates and are annealed in the presence of vacuum with 500 Oe magnetic field at 300 °C. Potassium has an ionic radius of 1.64 Å and replaces Bi, which has an ionic radius of 1.17 Å. Based on the ionic radii difference of Bi3+ and K+, the dopant concentration is varied in the range \({ {{{x}} =}}~0.0\) –0.3. X-ray diffractometer analysis shows that at \({{x}} {=} {0.3}\) an impurity phase (K2O) appears, which was not present at low dopant concentrations. It is shown here that ferromagnetic behavior arises in doped BiFeO3 films due to suppression of helical spin structure. In addition, as K+ replaces Bi3+ the charge compensation mechanism gives rise to oxygen vacancies and to the formation of Fe4+ cations, thus inducing ferromagnetic behavior. Variation in dopant concentration strongly affects the dielectric properties. Increase in dielectric constant up to \(\sim 84\) was observed with increase in dopant concentration up to 0.15. Decrease in dielectric constant ( \(\sim 25\) ), beyond 0.15 doping concentration, might have been observed because of the appearance of impurity phase as is observed in structural and magnetic properties. [ABSTRACT FROM PUBLISHER]

A series of single-phase nanocrystalline Mn0.5Cu0.5−xNixFe2O4 spinel ferrites with \(x = 0, 0.1, 0.2, 0.3, 0.4,~{\rm and}~0.5\) was successfully synthesized by sol-gel autocombustion method, at a temperature as low as 300 °C. X-ray diffraction, scanning electron microscopy, and room-temperature vibrating sample magnetometry studies have been carried out in order to understand the structural, morphological, and magnetic properties as a function of nickel concentration. The lattice parameters did not show any consistent decreasing or increasing trend, but crystallite size was decreased due to the incorporation of Ni contents at Cu sites in the structure. Large-sized grains were evident for the composition Mn0.5Cu0.5Fe2O4; however, the grain size was significantly reduced as the Ni was substituted. It was observed that with increasing nickel concentration, saturation magnetization increased, but coercivity decreased, which could be attributed to the substitution of soft ferromagnetic Ni2+ ions in place of diamagnetic Cu2+ ions. [ABSTRACT FROM PUBLISHER]

Effect of Pb doping on the structural and low temperature magnetic properties of SrPbxFe12-xO19 (x = 0, 0.1, 0.2, 0.3, and 0.4), synthesized by sol-gel autocombustion technique, has been investigated. The powder samples were sintered at 800°C for 2 h in order to develop the stable hexagonal phase, characteristic of the SrFe12O19 structure. The consequences of Pb substitution (at iron sites) on various structural parameters like lattice constants, unit cell volume, crystallite size, and porosity have been discussed. Fourier transform infrared frequency bands were utilized to determine the formation of tetrahedral and octahedral clusters of M-type ferrites. Hexagonal texture of the grains, a characteristic of the hexagonal crystal structure of SrFe12O19, was refined by Pb substitution.The magnetic properties, determined using a vibrating sample magnetometer, revealed that saturation magnetization decreased, while coercivity was increased with the increase of Pb contents. However, the increased squareness ratio and hence the energy product motivate the utilization of these ferrite compositions where hard magnetic characteristics are required.The increased values of saturation magnetization were observed at reduced temperature of 200 K, attributable to the better spin alignments of individual magnetic moments at low temperature. [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]

To explore the electrochemical performance, we synthesized a series of Ni-substituted ZnMn 2 O 4 using sol‒gel auto-combustion route. The formation of the tetragonal phase for ZnMn 2 O 4 and its transformation into a cubic phase upon Ni substitution is confirmed by the X-ray diffraction technique. Morphology analysis revealed that average particle size is increased from 150 to 250 nm when contents of Ni are increased from x = 0.0 to x = 1.0, respectively. Employing cyclic voltammetry and galvanostatic charge and discharge test, it is observed that pure ZnMn 2 O 4 has a specific discharge capacity of 11.2 F/g which decreased to 8.49 F/g for ZnMn 2 O 4. The tuning of this electrochemical performance is accredited to its hierarchical structure which facilitates charge transfer, large reaction surface area, and good structure stability. All these results validate that Zn 1-x Ni x Mn 2 O 4 composites are a suitable candidate as electrode material in supercapacitors. • Zn1-xNixMn2O4 (x = 0.00, 0.25, 0.50, 0.75 and 1.00) nano-spheres were synthesized using sol-gel auto-combustion method. •Phase transformation from tetragonal to cubic was confirmed by XRD. •Particle size slightly increased with increase of substitution contents. •Doping of Ni in place of Zn enhanced the electrochemical properties. •Outcomes of cyclic voltammetry and galvanostatic charge discharge test suggested that Zn1-xNixMn2O4 possessed ideal capacitive behavior, excellent electrochemical reversibility and rate capability. [ABSTRACT FROM AUTHOR]

Calcium (Ca) added bismuth iron oxide (Bi 1- x Ca x FeO 3) nanoparticles are synthesized using sol-gel method and studied under as-synthesized conditions. Calcium (Ca) concentration (x) is varied as 0.0, 0.1, 0.2, 0.3, 0.4 and 0.5. XRD results verify the formation of phase pure BiFeO 3 at dopant concentration x = 0.0–0.3. Raman analysis and EDX spectrum also confirm the formation and incorporation of Ca in the lattice. At x = 0.4 and 0.5 peaks corresponding to calcium oxide are observed. With addition of Ca ions in the lattice, strain is induced, resulting in reduced symmetry and increased inhomogeneity in the crystal structure. XPS analysis indicates small number of Fe2+ cations whereas no change in oxygen stoichiometry is observed. Size distribution and surface morphology of nanoparticles is observed using SEM and TEM images. Ca added bismuth iron oxide nanoparticles demonstrate ferromagnetic behavior where saturation magnetization increases from 9.202 emu/g to 21.097 emu/g as x increases from 0.0 to 0.3. This increase in saturation magnetization is accompanied by reduced magnetocrystalline anisotropy. High temperature magnetization curves indicate increase in magnetic ordering temperature from 643.7 K to 697 K. Field-cooled and zero field-cooled curves exhibit magnetic ordering with blocking temperature of ∼89 K under applied field of 500 Oe. P-E loops show high saturation polarization of 3.58 × 10−4 μC/cm2 for Ca concentration of x = 0.3. It is important to mention here that nanoparticles are synthesized without the use of any post thermal treatment. • Bi 1-x Ca x FeO 3 nanoparticles (x = 0.0–0.5) were synthesized with sol-gel method. • XRD results showed formation of BiFeO 3 phase at dopant concentration 0.0–0.3. • Saturation magnetization increased from 9.202 emu/g to 21.097 emu/g with reduced magnetocrystalline anisotropy. • Increase in magnetic ordering temperature from 643.7 to 697K was observed with increase in x from 0.0 to 0.3. • Blocking temperature of ∼88 K (applied field 500 Oe) was obtained using FC/ZFC curves. • Ferroelectric polarization loops showed highest value of polarization (3.58 × 10−4 μC/cm2) for Ca concentration of 0.3. [ABSTRACT FROM AUTHOR]