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High-performance colossal permittivity (ε′ > 104) plays an indispensable role in the development of electronic field. In this work, ultra-high dielectric permittivity (ε′ > 237, 294 @1 kHz) and low dielectric loss (0.012 @1 kHz) were simultaneously achieved in Ta-doped BaTi0.995Ta0.005O3 ceramics. Importantly, the dielectric permittivity changes less than 15% between − 55 and 200 °C, and the dielectric loss is less than 0.04. The excellent giant dielectric performance is related to the defect dipoles of electronic pins associated with electrons/oxygen vacancies/Ti3+, which are generated by B-site donor. And the thermal-activated short-range hopping of electrons is conformed to be the origin of low dielectric losses and excellent thermal stability. This work provides a strategy for achieving ultra-high dielectric permittivity, low dielectric loss, and excellent temperature stability of Ta-doped BaTiO3 simultaneously through B-site defect engineering. [ABSTRACT FROM AUTHOR]

A series of low-permittivity LiAl1 − xBxO2 (0.01 ≤ x ≤ 0.10) ceramics were fabricated by a conventional solid-state reaction method and were characterized for their phase evolution, crystal structure, and dielectric properties. Single-phase LiAl1 − xBxO2 solid solutions were formed at a limited compositional range (x = 0.05) while the secondary phase Li2(BAlO4) companied at higher dopant contents. Boron substitution facilitated the sintering behavior and optimized the densification of LiAlO2, resulting in dense microstructures and improved dielectric properties. A composition with x = 0.075 exhibited a high quality factor (Q×f) of 40,288 GHz along with a low relative permittivity (εr) of 6.3 and a temperature coefficient of resonance frequency (τf) of – 191 ppm/oC. All results indicate that the LiAl1 − xBxO2 ceramics can be a promising candidate material in the application of the substrate. [ABSTRACT FROM AUTHOR]

The tungsten bronze ceramics were prepared by solid-state reaction method to investigate the effect of La3+ concentration on the microstructure, dielectric and ferroelectric properties of Sr4 − xNa2 − xLaxTa0.6Nb9.4O30 (SNLTN: 0 ≤ x ≤ 0.4). X-ray diffraction results show that the tungsten bronze phase structure was a tetragonal phase in the P4bm space group at room temperature. The A-site structural vacancies increases as the structure transformed from “filled” to “unfilled” state. At the same time, the distortion of the BO6 octahedral increases. The results of the temperature dependence of the dielectric constant indicate that adding La3+ promotes the emergence of dipole-glass-like behavior and enhances dielectric relaxation. To better understand how polar clusters in Sr4 − xNa2 − xLaxTa0.6Nb9.4O30 ceramics change with increasing x, the size and kinetic behavior of PNRs were calculated and analyzed using the Vogel-Fulcher relationship and macroscopic and phenomenological statistical model, which reveals that the thermal stability of the dielectric constant is inversely related to the size of PNRs in addition to the long-range ordering of the system is disrupted. Hence, it is critical for the energy storage performance to obtain small size and the high number of active PNRs and the weak coupling between PNRs and other polar clusters. Finally, an energy storage density of 2.06 J/cm3 was received in Sr3.8Na1.8La0.2Ta0.6Nb9.4O30. [ABSTRACT FROM AUTHOR]

(1 − x)K0.5Na0.5NbO3–xLa(Zn0.5Zr0.5)O3 [(1 − x)KNN–xLZZ, x = 0.005, 0.010, 0.015, 0.020] ceramics were synthesized to fulfill the application requirement of high-temperature ceramic capacitors. The influence of LZZ content on the phase structure, microstructure morphology, dielectric and conductivity behaviors of this system was conducted. An orthorhombic phase for 0.005 ≤ x ≤ 0.010 and an orthorhombic-tetragonal coexisting phase for 0.015 ≤ x ≤ 0.020 were determined by the X-ray diffraction, Rietveld refinement, and dielectric spectra. The ceramic with x = 0.015 exhibits an ultrahigh and stable permittivity (ε' ~ 1892, ± 15% variation) and a low dielectric loss (tanδ ≤ 0.05) in a wide temperature region of 82–382 °C owing to the composition heterogeneity-induced shoulder-like peak and diffuse phase transition from tetragonal to cubic. The activation energies from the high-temperature dielectric relaxation and conductivity behaviors initially enhance greatly and then increase slowly, which could be related to the synergy effect of decreased oxygen vacancies and microstructure morphology evolution. [ABSTRACT FROM AUTHOR]

Compositional modification engineering was designed to simultaneously reduce the sintering temperature and improve the dielectric properties of BaTa2V2O11 via in-situ adjusting the V5+/Ta5+ molar ratio. A series of BaTa2-xV2+xO11 ceramics, fabricated by a solid-state reaction method, were characterized for structural evolution and dielectric properties variations. In-situ adjusting V5+/Ta5+ molar ratio significantly lowered the sintering temperature of BaTa2V2O11 and prominently improved the temperature stability of resonance frequency which is explained by the dielectric dilution theory. Competitive microwave dielectric properties with εr = 11.5–25.9, Q × f = 22,172–42,660 GHz, and τf = 42.4–74.6 ppm/ºC were achieved in the BaTa2-xV2+xO11 ceramics sintered at 620–840 oC. All the results indicate that the molar ratio of V5+ is primarily responsible for improving the densification behavior and dielectric characteristics of BaTa2-xV2+xO11, which in turn increases the appropriateness in further practical applications. [ABSTRACT FROM AUTHOR]

Quenching from sintering temperature enhances the depolarization temperature (Td) in Na1/2Bi1/2TiO3-based ceramics without significant deterioration of piezoelectric properties (d33). In this work, quenching effects in an ergodic relaxor 0.97(0.94Na0.5Bi0.5TiO3–0.06BaTiO3)–0.03AgNbO3 (NBT–6BT–3AN) were investigated based on structure, ferroelectric, and dielectric properties. The ergodicity to nonergodicity transition was obtained by quenching NBT–6BT–3AN above 1000 °C. The temperature stability of the quenching-induced nonergodicity was examined by annealing the quenched sample at 300 °C and 600 °C. The effect of oxygen vacancy on ergodicity to nonergodicity transition was investigated by comparing ferroelectric and electrostrain responses of the quenched and nitrogen-atmosphere-annealed samples. The influence of quenching on the structure including the average crystal structure, phase fraction and lattice distortion and the local structure including bond lengths and ordering of ions was analyzed. The ergodicity to nonergodicity transition upon quenching is ascribed to the contribution of the off-centered Bi3+ ions and ordered local structure. [ABSTRACT FROM AUTHOR]

In this study, Ba4RCo0.5Nb9.5O30 (R = La, Nd, Sm, Eu) (BRCN) ceramics were synthesized using a high-temperature solid-state reaction. The XRD refinement results show that ceramic samples are tetragonal tungsten bronze (TTB). As the radius of rare-earth ions decreases, the unit cell volume of BRCN ceramics decreases, and the radius difference between Ba2+ and R ions increase, which results in BO6 octahedral distortion and the Raman peaks shift to high frequency. In addition, as the radius of rare-earth ions decreases, the ionic displacements increase and thus the dielectric constant peak temperature goes up. The high-temperature impedance results show that there exists n-type electronic conduction in the samples. The remanent polarization of the P–E curve at low frequencies increases from 0.470 to 1.038 μC cm−2 as the rare-earth ion radius decreases. [ABSTRACT FROM AUTHOR]

The containerless method is generally used to study the intrinsic properties of materials, especially the thermophysical properties of melt droplets. The calculation of the melt droplet density and thermal expansion coefficient is related to its volume, while density is the dependent variable for determining the surface tension and viscosity coefficient. Evidently, the accuracy of the thermophysical properties of materials essentially depend on the precision of volume measurement. The melt droplet volume is obtained by analysing the image, thus, the precise volume of the melt droplet depends on the image quality and contour extraction algorithm. Restricted by external conditions, most of the obtained melt droplet images are of low quality and are severely polluted by noise, which complicates the determination of the thermophysical characteristics. Herein, a shape-supervised super-resolution convolutional neural network method is presented to improve image resolution and using its sub-network to extract the contour of the melt droplet directly and accurately. Compared with the existing method, this approach improves the accuracy of evaluating the thermophysical properties of the material and reduces the computational complexity by simplifying the two-step calculation process to a one-step procedure. [ABSTRACT FROM AUTHOR]

(1–x)K0.5Na0.5NbO3-xLaBiO3 [(1–x)KNN-xLB, x = 0, 0.005, 0.015] lead-free ceramics were prepared via a solid-state reaction route. An orthorhombic symmetry was determined for all samples by the Rietveld refinement of XRD patterns. The 0.995KNN-0.005LB ceramic (KNN-5LB) exhibits an ultrahigh and stable relative permittivity (ε' ~ 2158 ± 15%) with a low dielectric loss tangent (tanδ ≤ 3%) in a very broad operation temperature range from 172 °C to 450 °C due to two close diffuse phase transitions at ~200 °C and ~ 380 °C induced by La and an additional polarization from off-centered Bi ions. The Cole-Cole plot of iso-thermal complex impedance suggests that the high-temperature dielectric response of the KNN-5LB is attributed to the polarizations from grains, grain boundaries and electrode interfaces. Both the imaginary parts of impedance and modulus exhibit the thermally activated process and scaling behavior. The frequency dependent conductivity (σac) of the KNN-5LB follows the Universal Dielectric Response (UDR) law. The conduction mechanism is related to the small polaron hopping. [ABSTRACT FROM AUTHOR]

A new rock-salt type compound, namely Li3MgNbO5, was synthesized using traditional two-step sintering process for the first time. The products were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and thermal dilatometer and network analyzer. The Li3MgNbO5 ceramic sintered at 1260 °C adopted a cubic structure with Fm-3 m space group and exhibited excellent microwave dielectric properties (MDPs) of εr = 16.2, Q × f = 96796 GHz, and TCF = − 24.8 ppm/°C. The fitting results of the infrared spectrum indicated that the dielectric polarization of Li3MgNbO5 in microwave frequency band was contributed by phonon absorption in infrared band. Furthermore, the negative TCF value of Li3MgNbO5 ceramic was compensated with a traditional TCF compensator ~ CaTiO3. A near-zero TCF value of + 1.2 ppm/°C was achieved in the composite 0.96Li3MgNbO5–0.04CaTiO3 ceramics with εr = 18.4 and high Q × f = 86625 GHz, exhibiting a great potential to be applied in microelectronics systems. [ABSTRACT FROM AUTHOR]

Ta-doped 0.94Bi0.5Na0.5TiO3–0.06BaTiO3 [(1 − x)(0.94BNT–0.06BT) − xTa (x = 0.00–0.02)] ceramics were prepared by a solid-state reaction process. X-ray diffraction (XRD) shows a rhombohedral symmetry with space group R3c for all samples. The introduction of Ta moves the low-temperature dielectric anomaly to lower temperature while the high-temperature dielectric anomaly becomes broader, although the dielectric permittivity is depressed slightly. Dielectric permittivity (ɛr) as a function of temperature for the sample x = 0.02 shows a stable and broad relative permittivity ∼ 3500 from 50 °C to 400 °C with low dielectric loss (tanδ) ≤ 0.02 from 80 °C to 340 °C (at 1 kHz). A Debye-like relaxation was found in the paraelectric region. The activation energy of relaxation frequency (Ea) of the samples x = 0, 0.005, 0.01, 0.02 is 0.62 eV, 0.84 eV, 1.15 eV and 1.20 eV and the activation energy of conduction (Econ) is 0.56 eV, 0.72 eV, 0.89 eV and 0.90 eV for x = 0.00, x = 0.005, x = 0.01 and x = 0.02, respectively, which are derived from isothermal impedance spectroscopy and admittance spectroscopy, respectively. The dielectric relaxation behavior is related to the migration of oxygen vacancies and cation vacancies dependence on the concentration of Ta. [ABSTRACT FROM AUTHOR]

Recently, AgNbO3 antiferroelectric ceramics have attracted great attention by virtue of their characters of high energy storage density and environmental friendliness. To further optimize the electrical properties, in this work, Lu2O3 modified AgNbO3 ceramics were prepared via conventional solid state method. Crystal structure and element analysis indicated the Lu3+ ion preferred to enter the A-site when Lu2O3 content was lower than 2 mol%, otherwise, it was more likely to form LuNbO4 or Lu3NbO7-based solid solutions. Remarkably improved stability of antiferroelectric phase was observed once Lu3+ ions enter into the A-site, on account of the decrease of cell volume and tolerance factor. As a consequence, an enhanced recoverable energy storage density (Wrec) of 3.5 J/cm3 was achieved in 1 mol% Lu2O3 modified AgNbO3 ceramics at 210 kV/cm, which is superior to the other lead-free ceramics under moderate electric field (< 220 kV/cm). It is believed our study will provide a good reference for the development of AgNbO3-based dielectric capacitors. [ABSTRACT FROM AUTHOR]

The role of B-site ions of Bi0.5Na0.5TiO3 (BNT) on its complex phase transition remains unclear due to its polarization attributing to both Bi and Ti. In this paper, the phase transition of (Bi0.5Na0.5)0.94Ba0.06(Ti1−0.01b/4B0.01)O3 (BNT6BT) (B = Nb, Mn, Fe, and Cu) ceramics was modified by low-concentration donor doping (Nb) and acceptor doping (Mn, Fe, and Cu) in order to determine the origin of phase transition behavior. The phase structure, microstructure, local structure/lattice vibration, phase transition temperature, and dielectric properties of BNT6BT-Nb, Mn, Fe, and Cu ceramics were investigated. Results showed that all samples formed a single perovskite phase at room temperature, and donor (Nb) and acceptor (Mn, Fe, and Cu) doping can regulate the ratio of R3c and P4bm coexisting as nanoscale entities. The grains show polyhedral morphology, and average grain size lies between 1 and 2 μm. The Raman spectroscopy study shows that doping modification can change the phase transition temperature. The relation is in well agreement with the three different dielectric anomalies derived from the dielectric curves of εr versus T. Low concentration of cation (Nb, Mn, Fe, and Cu) doping can tailor the dielectric permittivity, depolarization temperature, and phase transition temperature of BNT6BT. All samples exhibit a large dielectric constant and good frequency stability. [ABSTRACT FROM AUTHOR]

Due to its good biodegradability and biocompatibility, polycaprolactone (PCL) has attracted widespread attention in the field of biomedical materials. Incorporation of Zinc oxide (ZnO) into PCL has been proved an effective way to improve its antibacterial properties. However, the interfacial compatibility of the organic-inorganic system needs to be improved due to the agglomeration of nanoparticles and phase separation of ZnO and PCL matrix affect its antibacterial efficiency. In this research, the ZnO surface was modified with citric acid monohydrate (CA) to improve the interfacial properties of ZnO-PCL system. The surface modification of ZnO was analyzed by DLS, TEM, TGA, and XPS. The results suggest that CA coating process can significantly reduce the agglomeration of ZnO nanoparticles and improve dispersion stability. The uniform PCL/ZnO-CA membranes with various nanofiller contents were fabricated through the solvent casting method. DSC and TGA analysis showed that the presence of ZnO-CA nanoparticles slightly decreased the crystallinity and thermal stability of the polymer. And ZnO-CA loaded improved the mechanical properties and wettability of the composite PCL membranes. Moreover, the composite PCL membranes showed good antibacterial activity against both E. coli and S. aureus while exhibiting good cytocompatibility, which indicated that the antibacterial and no cytotoxicity biomaterials had promising application in the biomedical field. [ABSTRACT FROM AUTHOR]

Amorphous Li–Si–Ti–P–O (LSTP) thin film electrolyte was successfully prepared by radio frequency magnetron sputtering using Li1.4Si0.4Ti1.6 (PO4)3 powder targets and stainless steel sheet as substrate. The effects of sputtering power on the structure, morphology, ionic conductivity, and electronic conductivity of the LSTP thin film electrolyte were investigated. The results showed that the LSTP thin film electrolyte obtained with sputtering power kept at 160 W, displayed uniform particles compacted in arrangement, proper stoichiometric ratio to the powder target as well as sufficient Li-ion for diffusion. Hence, it held a considerable ionic conductivity of 4.12 × 10−6 S cm−1 and a high σion/σele ratio about 8 magnitudes, indicating that it can be used as film electrolyte in all-solid-state lithium batteries. [ABSTRACT FROM AUTHOR]

High-temperature piezoelectric ceramics (0.95 − x)BiScO3–xPbTiO3–0.05Pb(Yb1/2Nb1/2)O3 (BS–xPT–PYN, x = 0.56–0.64) were prepared by a conventional solid-state reaction method. X-ray diffraction and Raman spectra demonstrated that the ceramics convert from monoclinic phase (x ≤ 0.58) to tetragonal phase (0.62 ≤ x ≤ 0.64). A phase coexistence of monoclinic and tetragonal in the vicinity of the MPB (x = 0.60) enhances the ferroelectric polarizability by a dynamical conversion between two energy-degenerate states with d33 = 392 pC/N, kp = 53.3% and Pr = 38.8 μC/cm2 and the operation temperature up to ~ 400 °C. Relaxor behaviors, which following the V–F law, are presented in this system and their dipole activation energy decrease for higher component x. The phase fraction versus temperature of the MPB (x = 0.60) was investigated by an in situ XRD, which gives an insight into the origin of the high-temperature piezoelectricity. [ABSTRACT FROM AUTHOR]

Mn contained ceramics with nominal formula Ba4RMn0.5Nb9.5O30 (R = La, Pr, Nd and Eu) were fabricated via a conventional solid−state reaction. The phase structure, microstructure, dielectric and ferroelectric properties of the materials were systematically studied. Ambient temperature XRD patterns indicate that all of the ceramics are single tetragonal tungsten bronze phase with space group P4bm. All of these ceramics present a broad permittivity peak, while only Ba4LaMn0.5Nb9.5O30 exhibits obvious frequency dispersion indicating relaxation. With decreasing A1-site ions size, the maximum dielectric constant temperatures (Tm) gradually increase. The relaxation activation energy and direct current conductivity activation energy of all compounds were obtained by linear fitting with Arrhenius equation. Furthermore, with the increase of the A1-site ions size, the Raman shift moves to a high frequency, indicating that different degrees of lattice distortion. Polarizations versus electric field (P–E) loops measured at ambient temperature show that Ba4EuMn0.5Nb9.5O30 has the highest remnant polarization value. [ABSTRACT FROM AUTHOR]

(1 − x)K0.5Na0.5NbO3-x(Bi0.5K0.5)ZrO3 [abbreviated as (1 − x)KNN-xBKZ, 0 ≤ x ≤ 0.08] lead-free ceramics have been fabricated by a solid-state processing route. Based on the x-ray diffraction data and temperature-dependent dielectric characteristics, an orthorhombic phase for x ≤ 0.03 and single rhombohedral one for x ≥ 0.05 at room temperature were determined. The cell volume firstly increases, then decreases and finally increases with increasing BKZ, depending on ionic size and crystallographic structure. For the sample of x = 0.05, a temperature-stable high permittivity (~ 1736 ± 15%) along with low dielectric loss tangent (≤ 5%) is recorded from 158°C to 407°C. In addition, the activation energies of dielectric relaxation and dc conductivity at high temperatures were characterized by impedance spectroscopy. A combined effect of lattice distortion and oxygen vacancies on the magnitude of activation energies was discussed. [ABSTRACT FROM AUTHOR]

The electric properties affected by the applying magnetic field or vice versa are known as magnetoelectric effect (ME effect), which caused great concern in recent years. Here, we reported the electric, magnetic and magnetoelectric properties of polycrystalline Y-type hexaferrite BaSrCo2Fe11.5Ga0.5O22. In particular, the frequency and temperature dependence of impedance, electric modulus, and ac conductivity, were studied. Grain and grain boundary effects were coexistent at low temperature of this sample, while at high temperature grain boundary effect was dominated. In addition, the universal power law (UPL) and superlinear power law (SLPL) regions were coexistent at low temperature. The magnetic transition temperature from helimagnetism to ferromagnetism was found at around 200 K. The magnetoelectric (ME) effect has been detected in the sample, and the ferroelectric polarization is induced by the magnetic field. What is more, the polarization can be reversed as the magnetic field changes signs. These results show that this ferrite is a good candidate for high temperature multiferroic applications and is also a good prototype for studying the SLPL mechanism in inorganic materials. [ABSTRACT FROM AUTHOR]

CaYCuTiO (0 ≤ x ≤ 0.67) ceramics were fabricated by a conventional solid-state reaction method. Lattice parameter of the system increases linearly with increasing x. The high-frequency dielectric loss of CaYCuTiO is suppressed significantly while the dielectric constant decreases slightly. The dielectric, impedance and modulus spectra reveals that the giant dielectric response associates with the Maxwell-Wagner effect. The decrease of dielectric constant is just related to the capacitance of grain boundaries. The dielectric relaxation behavior of the system is independent of Y substitution while the correlation between conductivity and frequency becomes stronger in Y substituted CaCuTiO. It suggests that space charge and long-range hopping of carriers play important roles on the low-frequency dielectric properties. The decrease of grain-boundary activation energy with Y substitution indicates that the concentration of oxygen vacancies increases in grain boundaries. The mechanisms of depressing low-frequency dielectric constant and high-frequency dielectric loss was discussed. [ABSTRACT FROM AUTHOR]

In order to found new dielectrics ceramics in tungsten bronze structure, unfilled tungsten bronze (TB) ceramics with nominal formula BaPrFeNbO were prepared by the solid state reaction method. The microstructure and dielectric properties were studied using powder X-ray diffraction, field emission scanning electron microscope, and variable temperature dielectric test system. The results show that the ceramics have a single phase and belong to the space group of P4bm with the cell of a = b = 12.4839(3) Å, c = 3.9409(5) Å, V = 614.192(2) Å. The frequency dependent dielectrics properties show that the ceramics have a Debye-like relaxation at room temperature, while the temperature dependent dielectrics properties indicate that the ceramics are a relaxor and the relaxation is due to the nanopolars and oxygen vacancies. The ceramics have a potential application in electronic ceramics as temperature-stable multilayer ceramic capacitors. [ABSTRACT FROM AUTHOR]

(1-x)Ba(FeNb)O -xBiYbO (BFN- xBY) ceramics were prepared by a conventional solid-state reaction method. The dielectric properties and relaxation behavior of BFN- xBY ceramics were analyzed according to dielectric and impedance spectroscopy. Dielectric permittivity of the ceramics increases with increasing temperature below 500 K then remains unchanged up to 700 K, while corresponding loss factor decreases with the increase of temperature below 500 K then increase slowly. Defect compensation mechanism of this system was analyzed in detail. The giant dielectric behavior of the ceramics arises from the internal barrier layer capacitor (IBLC) effect. Polarization effect at insulating grain boundaries between semiconducting grains accompanied by a strong Maxwell-Wagner (MW) relaxation mode. The characteristic of grain boundaries was revealed using impedance spectroscope and the universal dielectric response law. [ABSTRACT FROM AUTHOR]

0.4(BaCa)LaTiO-0.6Bi(MgTi)O ( x = 0.00, 0.15, 0.30) ceramics were prepared by a conventional mixed oxide route. Crystal structure of the ceramics was determined using XRD. Dielectric constant of the samples decreases with the increase of La content, however, the temperature stability of dielectric constant was improved. For x = 0.3, a near-plateau dielectric constant 700 ± 80, extended across the temperature range, 30-550 °C (at 1 kHz) was obtained. The corresponding loss tangent, tan δ, was ≤0.025 in the temperature range from 93 to 353 °C. All samples show a relaxor behavior and measurement frequency and the temperature ( T ) corresponding to the maximum of dielectric constant follow the Vogel-Fulcher relationship. Compared the dielectric properties of the samples with other materials, the former has highly attractive for developing capacitors over a wide working temperature range. [ABSTRACT FROM AUTHOR]

Y-type hexaferrites BaMgCoFeO ( x = 0.4, 0.8, 1.2, 1.6) were synthesized by solid state reaction method. The impedance spectrum, AC conductivity, and dielectric properties were investigated at various temperatures and in a wide range of frequency. The dielectric properties and AC conductivity have been explained on the basis of space charge polarization and the electric exchange between Fe and Fe as well as the hole hopping between Co and Co ions at octahedral side. The complex impedance analysis indicates the existence of space charge and the presence of electrical processes at increased temperatures. The change of the activation energy obtained from ln f versus 1/ T and ln σ versus 1/ T plots indicated that with increasing Co content, the transport mechanisms at low and high temperatures are different. Two magnetic phase transitions were observed in these samples and their transition temperatures increased with increasing Co doping. High Co content suppresses the second magnetic structure transition under an applied magnetic field. For all samples, the room temperature coercivity is less than 20 Oe, while the saturation magnetization increases with increasing Co content. The present work provides a fundamental understanding of the dielectric and conductivity mechanism of MgY type hexaferrite, which is essential for microwave and electronic applications in the materials. [ABSTRACT FROM AUTHOR]

Giant dielectric ceramics Ba(NbFeTi)O (BNFT) have been fabricated by a conventional solid-state reaction. According to X-ray diffraction analysis, the crystal structure of these ceramics can be described by the cubic centrosymmetric with Pm- 3m space group. The real part ( ε') of dielectric permittivity and dielectric loss (tan δ) of the BNFT ceramics was measured in a frequency range from 40 Hz to 100 MHz at room temperature. The ( ε') of all these samples displays a high value (~6500) and a small frequency-dependence from 1 kHz to 1 MHz. We have established a link between conductivity activation energy and defect compensation at grain boundaries. The Ti-doped Ba(NbFe)O as a donor makes a great influence on the grain boundary behavior, which restricts the migration of oxygen vacancy and depresses dielectric loss factor for Ba(NbFe)O ceramics. [ABSTRACT FROM AUTHOR]

(1− x)KNaNbO- xSrMnO (0.02 ≤ x ≤ 0.08) (KNN- xSM) ceramics were fabricated by a conventional solid-state technique. X-ray diffraction of the samples revealed that the crystal structure changes from orthorhombic to tetragonal, and finally to pseudocubic symmetry with increasing x. Temperature dependence of dielectric properties showed that the temperature ( T) corresponding to the maximum of dielectric permittivity decreased with increasing x. Two dielectric relaxation processes occurred at high temperatures, which were attributed to grain and grain boundary responses, respectively. Polarization hysteresis loops ( P- E) at different electrical fields were displayed. P degenerated with the increase of SM due to the thermally activated leakage current increases. The relationship between electrical properties and defect compensation mechanism is discussed. [ABSTRACT FROM AUTHOR]

Ferroelectric and magnetic properties of Fe-doped KNaLiNbO (KNLN) and Cu-doped KNLN ceramics were investigated. Comparing with pure KNLN ceramic, Fe-doped KNLN shows ferromagnetic and ferroelectric properties simultaneously while Cu-doped KNLN shows stronger diamagnetic and ferroelectric properties. The magnetic property in KNLN matrix are believed to be induced by point defects. The ferromagnetism of Fe-doped KNLN can be explained by the F-center exchange mechanism, while the antiferroelectric-like loop and diamagnetism of Cu-doped KNLN was explained by the special defect structure and Cu ion at A site. [ABSTRACT FROM AUTHOR]

In order to develop dielectric ceramics with temperature-stable permittivity characteristics, Eu and Ti co-doped KNaNbO [(1 − x)KNaNbO-xEuTiO] ceramics were prepared by a conventional solid state route. The effect of EuTiO on the phase structure and dielectric performance of KNN ceramics were investigated. The temperature dependence of the relative permittivity illustrated that the small amount of EuTiO depressed the dielectric peak of ferroelectric-paraelectric transition. Therefore, the temperature stability and relative permittivity of ceramics were effectively improved. As x = 0.03, the ceramic showed superior dielectric temperature stability (±10 %), very low dielectric loss (0.008 at 250 °C) and a relatively high permittivity (>1500 at 250 °C) over the temperature range from ~100 to 350 °C. It suggests that this ceramic is a promising candidate for high-temperature capacitor application. [ABSTRACT FROM AUTHOR]

Unfilled tungsten bronze ceramics with general formula KBaRNbO (R = La, Pr, Nd, Sm, Eu, Gd) were prepared by the conventional solid state reaction method. XRD patterns show that all ceramics are pure tungsten bronze phase. Dielectric characterization indicates that the ceramics except KBaGdNbO are relaxors with strong frequency dispersion, while KBaGdNbO shows diffuse phase transition and belongs to classical ferroelectrics. At room temperature, the KBaRNbO compounds (R = La, Pr, Nd) are paraelectrics while the KBaRNbO compounds (R = Sm, Eu, Gd) are ferroelectrics. Among them, KBaGdNbO has the highest remnant polarization (2 P) of 8.2 μC/cm. Phase transition temperature, remnant polarization (2 P) and tetragonality of the compounds increase with the decrease of ionic radius of the rare earths. [ABSTRACT FROM AUTHOR]

BaLa (ZrTi)O (BLZT) ceramics with x = 0.02 (BLZT-1), 0.04 (BLZT-2), 0.06 (BLZT-3) and 0.08 (BLZT-4) were prepared by a solid-state reaction route. Crystal structure of the BLZT ceramics was determined using X-ray diffraction and Raman spectroscopy. While the ceramics for x ≤ 0.04 are pure phase with cubic perovskite structure, pyrochlore LaZrO appears in the samples with x = 0.06 and 0.08. Dielectric properties as function of temperature and frequency showed more than one dielectric anomaly were found at high temperatures during heating but they weakened or disappeared during cooling. Both dielectric relaxation and electrical conductivity were taken into account in point defect mechanism. The double-ionized and short-range hopping of oxygen vacancy should be mainly responsible for the dielectric anomalies and conduction behavior. Activation energy of conductivity E is lower than half of the band gap E obtained by UV-Vis spectroscopy, which results from emergency of oxygen vacancies. In visible light region, the ceramics show a strong absorption with band gap of about 3.57 eV. [ABSTRACT FROM AUTHOR]

The dielectric properties and conductivity behavior of WO-doped KNa NbO ceramics were investigated as a function of temperature (25°C to 600°C) and frequency (40 Hz to 10 Hz). The dielectric loss and direct-current (DC) conductivity of the ceramics depend strongly on the tungsten content. A high-temperature dielectric relaxation near temperature of 500°C was observed and analyzed using the semiempirical complex Cole-Cole equation. The activation energy of the dielectric relaxation was estimated to be ∼2 eV and increased with increasing WO. The frequency-dependent conductivity can be well described by the universal dielectric response law. The activation energy obtained from the DC conductivity changes from 0.93 eV to 1.49 eV. A possible mechanism for the high-temperature dielectric relaxation and conductivity is proposed based on the activation energy value and defect compensation. [ABSTRACT FROM AUTHOR]

BiNaTiO (BNT)-doped BaFeNbO (BFN) ceramics were synthesized by a two-step solid-state reaction. Temperature dependence of dielectric properties measured at different frequencies was investigated over broad temperature and frequency ranges. Impedance spectroscopy and universal dielectric response were employed to study the relaxation behavior and conductivity mechanism of the ceramics in a frequency range from 40 Hz to 100 MHz and a temperature range from 300 K to 800 K. The complex plane impedance data revealed the bulk and grain boundary contributions toward conductivity processes in the form of semicircular arcs. The high-temperature conductivity of ceramics is attributable to thermally activated second ionized oxygen vacancy. [ABSTRACT FROM AUTHOR]

Several ferrum oxides of formula BaGdFeNbTaO (x = 2, 4, 6 and 8) with tetragonal tungsten-bronze structure have been synthesized by the conventional solid state sintering method. Dielectric response of the samples was studied using AC impedance spectroscopy and universal dielectric relaxation law in detail. The dielectric anomaly at high temperature is attributed to the mobility of oxygen vacancies. Arrhenius activation energy associated with the migration of oxygen vacancies is estimated from impedance spectroscopy, which is 0.77, 1.11, 1.26 and 1.02 eV for x = 2, 4, 6 and 8, respectively. [ABSTRACT FROM AUTHOR]

Two novel BaAFeTaO (A = K, Li) ceramics were fabricated through a conventional solid-state sintering process. Both samples were paraelectric phase with tetragonal tungsten bronze structure at room temperature. Dielectric response of the samples was studied by using AC impedance spectroscopy and universal dielectric relaxation law in detail. Dielectric relaxation at high temperatures is attributed to the oxygen vacancies induced by the evaporation of alkali oxide. The relaxation activation energy of the ceramics is lower than half of the band gap E obtained by UV-Vis spectroscopy, which resulted from the emergence of oxygen vacancies at high temperatures. In the visible light region, the samples showed strong absorption with a band gap of about 2.7 eV, which could be applied as a visible light irradiation photocatalyst. [ABSTRACT FROM AUTHOR]

(1 − x)BaTiO-xSrCaNaNbO [(1 − x)BT-xSCNN, 0 ≤ x ≤ 0.05] ceramics were prepared by conventional solid-state processing technique. Lorentzian function was used to fit the diffraction lines of the X-ray diffraction patterns, and obtained a structural phase transition from tetragonal to rhombohedral. The structural parameters were refined by the Rietveld method using Maud software from the X-ray diffraction patterns of BT-SCNN ceramics. The lattice parameters were found to decrease with increasing the concentration of SCNN. From the Arrhenius plots, the calculated activation energies of the relaxation and the conduction indicated that both the relaxation processes and conduction were thermally activated, and oxygen vacancies were the possible ionic charge carriers at high temperatures. The polarization study revealed a well-saturated hysteresis loop. [ABSTRACT FROM AUTHOR]

Giant dielectric ceramics CaCuTiO (CCTO) with non-ohmic electrical properties were prepared by a sol-gel processing method. Crystal structure and microstructure of the ceramics have been characterized using X-ray diffraction and Scanning electron microscopy. The effects of sintering duration and cooling rate on electrical properties of the ceramics were investigated by measuring the properties of permittivity, I- V and grain-boundary barriers. Prolonging holding time led to substantial improvement in permittivity, furthermore, the quenched sample showed larger dielectric permittivity than the furnace-cooling one. The non-ohmic behavior relating current density ( J) to the applied electric field ( E) at different temperatures was characterized. A low-voltage and giant dielectric permittivity CCTO varistor with breakdown voltages in the range of E = 0.2-3 kV cm, nonlinearity coefficient α = 2-6 and dielectric permittivity ε = 4,000-30,000 was obtained. A linear relationship between ln( J) and E indicated that a Schottky barrier should exist at the grain boundary. [ABSTRACT FROM AUTHOR]

(1 − x)(KNa)NbO-xSrBaNbO [(1 − x)KNN-xSBN] ceramics were synthesized by solid-state reaction technique. X-ray diffraction analysis of samples indicated that a single orthorhombic perovskite phase was formed as the x value is ≤0.02. Optimized piezoelectric properties with d = 126 pC/N, K = 0.39, Q = 201 were obtained for 0.98KNN-0.02SBN ceramic. The dielectric properties studies illustrated that both peaks of orthorhombic to tetragonal ( T) and ferroelectric tetragonal to paraelectric cubic ( T) phase transition shifted to lower temperature. The maximum remanent polarization ( P = 22.5 μC/cm) for 0.98KNN-0.02SBN was obtained by the polarization versus electric field ( P- E) researches. AC conductivity of samples increased with increasing the temperature. The calculated activation energy of the dc conductivity was 0.9654 eV, which may be due to thermal activation. [ABSTRACT FROM AUTHOR]

Dielectric spectroscopy was applied to porous nanocrystalline NaKNbO (NKN) ceramic green body, wherein influences of percolation effect and water adsorption at pore surface of the ceramic green body on dielectric response were examined over wide temperature (150 to 450 K) and frequency (100 Hz to 1 MHz) ranges. Dielectric permittivity of the ceramic green body is about 2-3 orders of magnitude higher than that of pure NKN powder or NKN ceramic. Furthermore, the high dielectric permittivity and high humidity sensitivity of the ceramic green body can appear again with aging a period of time in air. The data from this investigation make potential applications for NKN as a giant dielectric material or a humidity sensing material. [ABSTRACT FROM AUTHOR]

In order to conciliate dielectric and non-Ohmic properties of CaCuTiO (CCTO) ceramics, NiO, SnO, SiO, and AlO were added as sintering aids to promote the grain growth of CCTO ceramics. Microstructure, dielectric properties, and non-Ohmic behavior of the CCTO ceramics were investigated. Among them, NiO-modified CCTO exhibits good dielectric and non-Ohmic properties ( ε = 69833, tan δ = 0.073, α = 3.66 and E = 296.7 V/cm), due to NiO is also one of giant dielectric materials. Therefore, it is suitable for applying semiconductor circuits. The relationship between electrical current density ( J) and electrical field ( E) demonstrated that Schottky barrier should exist at grain boundaries. Non-linear coefficient α was directly proportional to the height of barrier. Depressing barrier width would improve significantly dielectric permittivity but decrease breakdown voltage. [ABSTRACT FROM AUTHOR]

BaGdFeNbTaO was synthesized by a standard solid-state technique, which adopts a tetragonal filled tungsten bronze structure and exhibits paraelectric nature at room temperature. The dielectric temperature coefficient of BaGdFeNbTaO at 1 MHz is 147 ppm °C AC impedance plots were used as tools to analyze the electrical behavior of the sample as a function of frequency at different temperatures. The conduction is a thermally activated process with activation energy ~1.30 eV. The frequency-dependent maxima in the imaginary part of impedance are found to obey an Arrhenius law with activation energy ~1.34 eV. Such a value of activation energy suggests the existence of a relaxation mechanism (a conductive process), which may be interpreted by an ion hopping between neighboring sites within the crystalline lattice. [ABSTRACT FROM AUTHOR]

Sodium potassium niobate KNaNbO(KNN) ceramic was synthesized by a solid-state technique. The X-ray diffraction of the sample at room temperature showed a monoclinic phase. The real part ( ε′) and imaginary part ( ε″) of dielectric permittivity of the sample were measured in a frequency range from 40 Hz to 1 MHz and in a temperature range from 350 to 850 K. The ε′ deviated from Curie-Weiss law above 702 K, due to additional dielectric contributions resulting from universal dielectric response and thermally activated space charges at high temperatures. This anomaly arose from a Debye dielectric dispersion that slowed down following an Arrhenius law. We have established a link between the dielectric relaxation and the conductivity. [ABSTRACT FROM AUTHOR]

(1 − x)K0.5Na0.5NbO3-x(Bi0.5Li0.5)ZrO3 (labeled as (1 − x)KNN-xBLZ) lead-free ceramics were fabricated by a solid-state reaction method. A research was conducted on the effects of BLZ content on structure, dielectric properties and relaxation behavior of KNN ceramics. By combining the X-ray diffraction patterns with the temperature dependence of dielectric properties, an orthorhombic-tetragonal phase coexistence was identified for x = 0.03, a tetragonal phase was determined for x = 0.05, and a single rhombohedral structure occurred at x = 0.08. The 0.92KNN-0.08BLZ ceramic exhibits a high and stable permittivity (~ 1317, ± 15% variation) from 55 to 445 °C and low dielectric loss (≤ 6%) from 120 to 400 °C, which is hugely attractive for high-temperature capacitors. Activation energies of both high-temperature dielectric relaxation and dc conductivity first increase and then decline with the increase of BLZ, which might be attributed to the lattice distortion and concentration of oxygen vacancies. [ABSTRACT FROM AUTHOR]

A correction to the article "Dielectric behavior of La2O3- modified 0.4(Ba0.8Ca0.2) TiO3–0.6Bi(Mg0.5Ti0.5)O3 lead-free ceramics" by Xiaoqi liu that was published in a previous issue of the periodical is presented.