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0.6Bi(Mg1/2Ti1/2)O3–0.4Ba0.8Ca0.2(Nb0.125Ti0.875)O3 ceramics with a pseudo-cubic structure and re-entrant dipole glass behavior have been investigated via x-ray diffraction and dielectric permittivity–temperature spectra. It shows excellent dielectric–temperature stability with small variations of dielectric permittivity (±5%, 420–802 K) and dielectric loss tangent (tanδ < 2.5%, 441–647 K) in a wide temperature range. Three dielectric anomalies are observed from 290 to 1050 K. The low-temperature, weakly coupled re-entrant relaxor behavior was described using the Vogel–Fulcher law and the new glass model. The mid- and high-temperature dielectric anomalies are characterized by isothermal impedance and electrical modulus. The activation energy of both dielectric relaxation and conductivity follows the Arrhenius law in the temperature ranges of 633–753 and 833–973 K, respectively. The ultrahigh thermal stability of dielectric permittivity is attributed to the weak coupling of polar clusters, the formation of diffuse phase transition, and the local phase transition of calcium-containing perovskite. The results provide new insights into the defects behavior and the modification way of re-entrant relaxor behavior. [ABSTRACT FROM AUTHOR]

The 0.55Bi(Mg1/2Ti1/2)O3–0.45PbTiO3 ceramics exhibit notable dielectric anomalies across three temperature ranges. The low‐temperature anomaly is attributed to a reentrant dipole glass‐like relaxor behavior; the mid‐temperature anomaly results from a ferro‐paraelectric phase transition; and the high‐temperature anomaly is associated with a diffuse phase transition. The system demonstrates favorable piezoelectric, electromechanical, and ferroelectric properties. Specifically, the ceramic presents a piezoelectric coefficient (d33) of 220 pC/N, an electromechanical coupling factor (kp) of 27%, and a remanant polarization (Pr) of 32.5 μC/cm2. Moreover, it maintains an operational capability up to 643 K. The unsaturated P(E) loops are formed through the coupling polarization between polar nanoregions (PNRs) and P4mm ferroelectric domains. By examining the electrical modulus, the dynamic PNRs resulting from ferroelectric phonon localization and the formation of P4mm ferroelectric domains were analyzed. The result reveals a mesoscale coupling relationship between the origin of high‐temperature piezoelectric stability and the dynamics of PNRs, thereby providing noble insights into the (1 − x)BiMeO3–xPbTiO3 system. [ABSTRACT FROM AUTHOR]

Bismuth sodium titanate (BNT)-based, lead-free piezoelectric materials have been extensively studied due to their excellent strain characteristics and environmental friendliness. In BNTs, the large strain (S) usually requires a relatively large electric field (E) excitation, resulting in a low inverse piezoelectric coefficient d33* (S/E). Moreover, the hysteresis and fatigue of strain in these materials have also been bottlenecks impeding the applications. The current common regulation method is chemical modification, which mainly focuses on forming a solid solution near the morphotropic phase boundary (MPB) by adjusting the phase transition temperature of the materials, such as BNT-BaTiO3, BNT-Bi0.5K0.5TiO3, etc., to obtain a large strain. Additionally, the strain regulation based on the defects introduced by the acceptor, donor, or equivalent dopant or the nonstoichiometry has proven effective, but its underlying mechanism is still ambiguous. In this paper, we review the generation of strain and then discuss it from the domain, volume, and boundary effect perspectives to understand the defect dipole behavior. The asymmetric effect caused by the coupling between defect dipole polarization and ferroelectric spontaneous polarization is expounded. Moreover, the defect effect on the conductive and fatigue properties of BNT-based solid solutions is described, which will affect the strain characteristics. The optimization approach is appropriately evaluated while there are still challenges in the full understanding of the defect dipoles and their strain output, in which further efforts are needed to achieve new breakthroughs in atomic-level insight. [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]

The existence of polar nanoregions (PNRs) is the most important characteristic of ferroelectric relaxors; however, the size determination and the dynamic of PNRs remain uncertain. Herein, it is revealed that a re‐entrant relaxor behavior and ferroelectric–paraelectric transition coexist in complex perovskite oxide 0.6Bi(Mg1/2Ti1/2)O3‐0.4PbTiO3. Two dielectric anomalies, 1) the low‐temperature re‐entrant relaxor transition and 2) the high‐temperature diffuse phase transition (DPT), are described by the phenomenological statistical model. The sizes of the two kinds of PNRs corresponding to two ferroelectric states were obtained. The dynamics of PNRs are analyzed using isothermal electrical modulus, which shows three critical temperatures associated with the DPT, the formation, and freezing of PNRs, respectively. The temperature evolution of the PNRs evolution depends on the stoichiometry of bismuth. The results provide new insights into the dynamic behavior of PNRs and the modification way of re‐entrant relaxor behavior. [ABSTRACT FROM AUTHOR]

Doping is a widely used method to tune the physical properties of ferroelectric perovskites. Since doping can induce effective charges, it is important to understand how charges affect the chemical and physical properties of the doped perovskites. Here, we propose two charge compensation models, by adding the charge‐dipole interaction to the effective Hamiltonian, which has not been done previously, and numerically investigate how lanthanum doping affects the ferroelectric phase transition temperature and the hysteresis loop in BaTiO3. The consequences of the charge compensation models are compared and discussed, revealing that the electron compensation mechanism with some Ti4+ ions changing to Ti3+ is critical to understanding the donor‐doped perovskites. [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]

It has been a challenge to provide a unified description of the dielectric response vs temperature for ferroelectrics with diffuse phase transition (DPT) and relaxor behaviors, which can be used to fit the dielectric response both below and above the peak temperature (Tm). Most of the available functions used in fitting experimental data only provide a description of the dielectric permittivity near and above Tm. In this work, employing a macroscopic and phenomenological statistical model and using Ba(Ti1−x Zrx)O3 ceramics as an example, we revisit the dielectric permittivity's temperature dependence, analyzing their DPT and relaxor behaviors and providing a complete description over the whole temperature range. We show that good agreements between theoretical and experimental results can be achieved. To better understand how Ba(Ti1−x Zrx)O3 ceramics changes from DPT to relaxor with increasing x, we also discuss the relation between the fitting parameters and Ba(Ti1−x Zrx)O3's composition and structure, which suggests that the parameters from the statistical model reflect the size of the correlated Ti ions (small clusters or polar nanoregions), which largely determine the behavior of Ba(Ti1−x Zrx)O3 ceramics. [ABSTRACT FROM AUTHOR]

It has been a challenge to provide a unified description of the dielectric response vs temperature for ferroelectrics with diffuse phase transition (DPT) and relaxor behaviors, which can be used to fit the dielectric response both below and above the peak temperature (Tm). Most of the available functions used in fitting experimental data only provide a description of the dielectric permittivity near and above Tm. In this work, employing a macroscopic and phenomenological statistical model and using Ba(Ti1−x Zrx)O3 ceramics as an example, we revisit the dielectric permittivity's temperature dependence, analyzing their DPT and relaxor behaviors and providing a complete description over the whole temperature range. We show that good agreements between theoretical and experimental results can be achieved. To better understand how Ba(Ti1−x Zrx)O3 ceramics changes from DPT to relaxor with increasing x, we also discuss the relation between the fitting parameters and Ba(Ti1−x Zrx)O3's composition and structure, which suggests that the parameters from the statistical model reflect the size of the correlated Ti ions (small clusters or polar nanoregions), which largely determine the behavior of Ba(Ti1−x Zrx)O3 ceramics. [ABSTRACT FROM AUTHOR]

Phase diagram of the solid solution system K 0.5 Na 0.5 NbO 3 - Bi ½ Na ½ TiO 3 [(1-x)KNN-xBNT] has been established from dielectric permittivity measurement and structure analyses. The unit cell volumes continuously decrease depending on the composition, while the local structure maintains distortions away from the cubic average structure in the range 0.10 ≤ x ≤ 0.90. No clear correspondence for the temperatures of phase transition exists between structural studies and physical properties. The dielectric behavior is depicted successively from normal ferroelectric, diffuse phase transition, re-entrant-like relaxor, relaxor + dipolar glass-like relaxor, BNT-like relaxor with the increase of BNT. A comprehensive composition-property phase diagram for this system has been given to understand the various ferroelectric phenomena. The result could be mainly elucidated by the nanoclusters and the disorder driven nucleation of polar nanoregions contributed by a valence mismatch at one of the cation sites. [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]

A perovskite solid solution of (1-x)(Bi0.5Na0.5)TiO3-x(Na0.5K0.5)NbO3 (BNT-xNKN) (x = 0–0.08) synthesized by solid state reaction technique exhibits diffuse phase transition (DPT) behavior. Power law, Gauss-type quadratic law and Lorenz-type quadratic law was employed to characterize the dielectric permittivity peaks near Tm . The diffuseness parameters γ, δG and δA increase with the increase in the value of x, which implies a composition-induced diffuse transition. Among these laws simulating dielectric response in diffusion ferroelectric phase transition, the Lorenz-type quadratic law is the best to describe the characterization of DPT behavior in such a wide temperature range as observed in our experiment. [ABSTRACT FROM PUBLISHER]

Abstract: A/B-site complex perovskite (NaBi(1−x)K x )0.5Ti(1−x)Nb x O3 (also can be written: (1−2x)Na0.5Bi0.5TiO3–xK0.5Bi0.5TiO3–xNaNbO3) (x =0–0.08) lead-free piezoelectric ceramics were fabricated by mechanical alloying technique from their oxide/carbonate mixture. Phase evolvements of the mixture and the influence of x value on crystal structure and microstructure were investigated. The perovskite Na0.5Bi0.5TiO3 phase was progressively formed with passing through the intermediate Bi4Ti3O12 phases with increasing degree of mechanical activation. The Curie–Weiss law and a modified empirical expression were employed to describe the ferroelectric phase transition of (NaBi(1−x)K x )0.5Ti(1−x)Nb x O3 ceramics. The results showed that (NaBi(1−x)K x )0.5Ti(1−x)Nb x O3 ceramics became more relaxor ferroelectric characteristic with the increase in value of x. The enhancement of relaxor characteristic may arise from structural disorder and compositional fluctuation in the crystal structure. [Copyright &y& Elsevier]

Ba4Ln2Fe2Nb8O30 (Ln = Eu and Gd) ceramics were synthesized by high temperature solid state reaction. The phase composition, microstructure, dielectric and ferroelectric properties of them were characterized. Both ceramics adopt filled tetragonal tungsten bronze structure at room temperature. The diffusive phase transitions were observed for Ba4Eu2Fe2Nb8O30 and Ba4Gd2Fe2Nb8O30 around 163°C and 150°C, respectively. Ba4Eu2Fe2Nb8O30 and Ba4Gd2Fe2Nb8O30 ceramics are classical ferroelectrics at room temperature and show high dielectric constant of 118 and 160 and low dielectric loss 0.022 and 0.054 at 1 MHz, respectively. The remnant polarizations (2Pr) are 3.9μC/cm2 for Ba4Eu2Fe2Nb8O30 and 1.71μC/cm2 for Ba4Gd2Fe2Nb8O30. [ABSTRACT FROM AUTHOR]

0.6Bi(Mg1/2Ti1/2)O3–0.4Ba0.8Ca0.2(Nb0.125Ti0.875)O3 ceramics with a pseudo-cubic structure and re-entrant dipole glass behavior have been investigated via x-ray diffraction and dielectric permittivity–temperature spectra. It shows excellent dielectric–temperature stability with small variations of dielectric permittivity (±5%, 420–802 K) and dielectric loss tangent (tanδ < 2.5%, 441–647 K) in a wide temperature range. Three dielectric anomalies are observed from 290 to 1050 K. The low-temperature, weakly coupled re-entrant relaxor behavior was described using the Vogel–Fulcher law and the new glass model. The mid- and high-temperature dielectric anomalies are characterized by isothermal impedance and electrical modulus. The activation energy of both dielectric relaxation and conductivity follows the Arrhenius law in the temperature ranges of 633–753 and 833–973 K, respectively. The ultrahigh thermal stability of dielectric permittivity is attributed to the weak coupling of polar clusters, the formation of diffuse phase transition, and the local phase transition of calcium-containing perovskite. The results provide new insights into the defects behavior and the modification way of re-entrant relaxor behavior. [ABSTRACT FROM AUTHOR]

The 0.55Bi(Mg1/2Ti1/2)O3–0.45PbTiO3 ceramics exhibit notable dielectric anomalies across three temperature ranges. The low‐temperature anomaly is attributed to a reentrant dipole glass‐like relaxor behavior; the mid‐temperature anomaly results from a ferro‐paraelectric phase transition; and the high‐temperature anomaly is associated with a diffuse phase transition. The system demonstrates favorable piezoelectric, electromechanical, and ferroelectric properties. Specifically, the ceramic presents a piezoelectric coefficient (d33) of 220 pC/N, an electromechanical coupling factor (kp) of 27%, and a remanant polarization (Pr) of 32.5 μC/cm2. Moreover, it maintains an operational capability up to 643 K. The unsaturated P(E) loops are formed through the coupling polarization between polar nanoregions (PNRs) and P4mm ferroelectric domains. By examining the electrical modulus, the dynamic PNRs resulting from ferroelectric phonon localization and the formation of P4mm ferroelectric domains were analyzed. The result reveals a mesoscale coupling relationship between the origin of high‐temperature piezoelectric stability and the dynamics of PNRs, thereby providing noble insights into the (1 − x)BiMeO3–xPbTiO3 system. [ABSTRACT FROM AUTHOR]

Abstract: We report the temperature-dependent x-ray powder diffraction of the Na0.5K0.5NbO3 (NKN)-based piezoelectric ceramics in the range between 320 and 700K. In the case of NKN we have detected the structural phase transition region from the orthorhombic phase to the tetragonal phase over a broad temperature range from 496 to 458K. The region is enlarged and shifted to lower temperature by introducing trace impurity or second component. It is considered that the coexistence of orthorhombic and tetragonal phases in NKN-based ceramics observed near room temperature are essentially due to the shift and enlargement of the phase coexistence region induced by lattice chemical pressure. [Copyright &y& Elsevier]

The crystal structure of (1-x)BaTiO3-xBiAlO3 (x = 0, 0.02, 0.05, 0.08, and 0.1) ceramics was determined using X-ray diffraction and Raman spectroscopy at room temperature, which revealed a phase transition from tetragonal to rhombohedral with increasing x. The dielectric properties were studied as a function of temperature at different frequencies, which indicated that the phase transition temperature (Tm) decreased with increasing x. The relaxor behavior was observed by frequency and temperature dependent dielectric permittivity. The Lorenz-type quadratic law was used to characterize the dielectric permittivity peaks near Tm of high-temperature slopes at 1 MHz. The temperatures Tm of dielectric permittivity peaks fit very well with the Vogel-Fulcher law in x = 0.05 and x = 0.1. The polarization hysteresis loops and electrostrictive were displayed at room temperature. The sample for x = 0.1 exhibits a slim loop with negligible hysteresis and a subtle linear feature, which is a promising transducer material for use as an active element. [ABSTRACT FROM AUTHOR]

(1 − 0.5x)BaTiO3–0.5x (0.4BaZrO3–0.6CaTiO3) (0 ⩽ x ⩽ 0.875) ceramics were fabricated by a conventional solid-state technique. The influence of the substitution content on crystallographic structure, phase transition, piezoelectric and ferroelectric properties was investigated. A morphotropic phase boundary from a cubic–rhombohedral–tetragonal tricritical triple point was found in x = 0.375–0.500. The sample with x = 0.375, sintered at a lower temperature (1623 K), showed excellent piezoelectric performance (d33 = 420 pC N−1, kp = 57%, Qm = 120.2 and TC = 380 K) and good thermal stability up to 370 K. [ABSTRACT FROM AUTHOR]

Low band gap ferroelectrics that exhibit high polarization at ambient conditions are highly desirable for achieving efficient charge carrier separation in photovoltaic applications. In this work, a well-designed Co/Nb-modified Bi 0.5 Na 0.5 TiO 3 system (1- x)Bi 0.5 Na 0.5 TiO 3 - x CaCo 0.5 Nb 0.5 O 3 with x =0.00–0.20 offers a platform with the characteristics of low band gap and high ferroelectric polarization simultaneously. A structural phase transition from rhombohedral to monoclinic structure as the x content increases, which is verified by XRD analysis. Specifically, the x =0.10 ceramic exhibited a considerable high remanent polarization of 20.2 μC/cm2 and a low band gap of 2.18 eV, approximately 31% lower than that for a pure BNT sample (∼3.13 eV). However, the leakage current significantly increased with an increase in the x content, where it exceeded by more than three orders of magnitude for the x =0.20 sample in comparison to the pure BNT sample. Current-voltage characteristics revealed that space-charge-limited conduction was the primary conduction mechanism within the ceramics with x <0.20, which can be attributed to the free carriers confined by oxygen vacancies. On the other hand, field-assisted ionic conduction was revealed to be the primary conduction mechanism in the sample corresponding to x =0.20 at room temperature. We ascribe these mechanisms to oxygen vacancies and multivalent cobalt ions based on the XPS analysis. An improved understanding of conduction mechanism sheds light on leakage current problems and facilitates the design of BNT-based ferroelectric devices with excellent insulating character for high-performance photoelectric and photovoltaic applications. • We well-designed Co/Nb-modified Bi 0.5 Na 0.5 TiO 3 system (1- x)Bi 0.5 Na 0.5 TiO 3 - x CaCo 0.5 Nb 0.5 O 3 with x =0.00–0.20 provides a unique platform with the simultaneous optimization of low band gap and high ferroelectric polarization. • The ceramic with x =0.10 exhibits a considerable high spontaneous polarization of 20.2 μC/cm2 and a low band gap of 2.18 eV, approximately 31% lower than that for a pure Bi 0.5 Na 0.5 TiO 3 sample (∼3.13 eV). • The space charge limited conduction is dominant conduction mechanism for x <0.20 samples, which associates with the free-carriers trapped by the oxygen vacancies, whereas the field-assisted ionic conduction is dominant in x =0.20 sample at room temperature. [ABSTRACT FROM AUTHOR]

The existence of polar nanoregions (PNRs) is the most important characteristic of ferroelectric relaxors; however, the size determination and the dynamic of PNRs remain uncertain. Herein, it is revealed that a re‐entrant relaxor behavior and ferroelectric–paraelectric transition coexist in complex perovskite oxide 0.6Bi(Mg1/2Ti1/2)O3‐0.4PbTiO3. Two dielectric anomalies, 1) the low‐temperature re‐entrant relaxor transition and 2) the high‐temperature diffuse phase transition (DPT), are described by the phenomenological statistical model. The sizes of the two kinds of PNRs corresponding to two ferroelectric states were obtained. The dynamics of PNRs are analyzed using isothermal electrical modulus, which shows three critical temperatures associated with the DPT, the formation, and freezing of PNRs, respectively. The temperature evolution of the PNRs evolution depends on the stoichiometry of bismuth. The results provide new insights into the dynamic behavior of PNRs and the modification way of re‐entrant relaxor behavior. [ABSTRACT FROM AUTHOR]

Abstract: Multiferroic solid solution of (1 − x)PbTiO3 − xNdFeO3 (PT − NF) compounds are synthesized by a conventional solid state reaction. XRD investigations indicate the phase PT − NF transition from tetragonal to pseudo-cubic and then orthorhombic phase by increasing the dopant NdFeO3. The multiferroic and magnetoelectric (ME) behaviors in (1 − x)PbTiO3 − xNdFeO3 solid solutions are observed in the tetragonal phase (0 ≦ x ≦ 0.3). Further addition of the dopant NdFeO3 results into severe leakage currents and phase transitions. The solid solution compounds achieve strong ferromagnetism with high remnant magnetization (Mr = 0.786 emu/g) at x = 0.8. This work demonstrates a way to tailor the ferroelectric, magnetic properties and ME coupling in multiferroic PT-based compounds. [Copyright &y& Elsevier]

Abstract: 0.92K0.5Na0.5NbO3–(0.08− x)Bi0.5Li0.5TiO3–xBaZrO3 (KNN–BLT–BZ) lead-free piezoelectric ceramics were fabricated by traditional ceramics process. XRD results showed that complete solid solutions with mixed phases of rhombohedra and tetragonal were observed. Diffusion phase transitional behavior, dielectric properties and ferroelectric properties of the KNN–BLT–BZ ceramics were investigated. It was found that the cubic-tetragonal phase transition temperature (T C ) slightly decreased as the amount of BaZrO3 was increased. A morphotropic phase boundary (MPB) between rhombohedral and tetragonal ferroelectric phases was identified in the composition range of 0.04≤ x ≤0.06. Furthermore, good ferroelectric properties were also found in this composition range, with P r of 14.5μCcm−2 and E c of 1.95kVmm−1 for the sample with x =0.04. [Copyright &y& Elsevier]

It is of importance to discover new type ferroelectric materials with enhanced functionalities to meet various demand of applications, here we prepared the BaBi 2 Ta 2 O 9 ceramic with orthogonal structure and oxygen octahedral rotation. This type of material had been screened out to be a candidate ferroelectric previously based on high-throughput first-principles density functional theory (DFT) calculations. The relationship between local phase structure and ferroelectric properties of this system is investigated by dielectric spectrum. Low-temperature relaxor behavior is described by using the Curie-Weiss law and the Vogel-Fulcher relationship. The polarization response and size of Polar nanoregions (PNRs) are described using the phenomenological statistical model. The P (E) loops imply that long-range-order ferroelectric is destroyed formation frozen randomly interacting PNRs. Element segregation and lattice distortion are directly observed using TEM, which is associated with the substitution of multiple atoms for the one cation occupation. • A novel Bi-layered structure ferroelectric BaBi2Ta2O9 screened out by high-throughput first-principles DFT was prepered. • BaBi2Ta2O9 is a ferroelectrric relaxor and shows an orthorhombic structural with space group Cmc21. • In situ Raman spectrotra enclosed a phase transition from non-centrosy symmetric phase to centrosy symmetric phase at 673K. • The size of PNRs of BaBi2Ta2O9 was determined by the phenomenological model and atomic scale morphological was observed by spherical aberration electron microscope. [ABSTRACT FROM AUTHOR]

Abstract: Series new Ba4RETiNb9O30 (RE=La, Pr, Nd, Sm, Eu, Gd) compounds and ceramics were prepared by solid state reaction method respectively. The phase structure, microstructure, dielectric and ferroelectric properties of obtained ceramics were systematically investigated. The XRD results show that all ceramics have been determined as pure tungsten bronze phase. The dielectric characterization indicates that the former four ceramics are relaxors with strong diffuse phase transition and frequency dispersion, while the latter two ceramics show diffuse phase transition. Phase transition temperatures and tetragonality of tungsten bronze structure increase with the decrease of the radii of rare earth. All ceramics have ferroelectricity, among them Ba4GdTiNb9O30 has the highest remnant polarization (2Pr) of 5.12μC/cm2. [Copyright &y& Elsevier]

• Na 2 CaV 4 O 12 was prepared at extremely low temperatures (350–550 °C). • in-situ XRD reveals a phase transition from P 4/ nbm to P 4 ̅ b 2 at 510 °C. • A strong correlation between ionic conductivity and phase structure of Na 2 CaV 4 O 12. • Bond valence-based energy landscape calculations disclosed a two-dimensional interstitial diffusion mechanism. Alkaline earth metal vanadates have drawn attention because of their potential applications in electrochemical devices. Here, Na 2 CaV 4 O 12 was prepared at extremely low temperatures (350–550 °C) and showed a semiconductor behavior with a bandgap of 2.92 eV. A phase transition from P 4/ nbm to P 4 ̅ b 2 occurred at 510 °C was identified by an in-situ XRD upon heating, where the 16 n site for oxygen atoms in the P 4/ nbm phase evolves into two distinguishable 8 i sites in the P 4 ̅ b 2 phase. Ionic conduction in Na 2 CaV 4 O 12 at elevated temperatures was reported for the first time in the present work. A strong correlation between ionic conductivity and phase structure of Na 2 CaV 4 O 12 is observed. The charged carriers are mainly sodium ions for the low-temperature P 4/ nbm phase, while mixed conduction contributed by sodium ions and oxide ions happened in the transformed phase. Bond valence-based energy landscape calculations disclosed a two-dimensional interstitial diffusion mechanism for Na+ ions in the Na 2 Ca-layers, as well as a two-dimensional diffusion mechanism for oxide ions in the V 4 O 12 -layers. The novel semiconductor ceramic would have potential applications in all-solid sodium ions batteries or solid oxide fuel cells as electrolytes. [ABSTRACT FROM AUTHOR]

Abstract: (1− x)BaTiO3–xBi(Zn0.5Zr0.5)O3 [(1− x)BT–xBZZ, 0.01⩽ x ⩽0.6] ceramics were synthesized by solid-state reaction technique. Based on the X-ray diffraction data analysis, a systematic structure change from the ferroelectric tetragonal phase to pseudocubic phase and the pseudocubic phase to orthorhombic phase was observed near x =0.07 and x =0.4 at room temperature, respectively. Dielectric measurements show a dielectric anomaly, over the temperature range from 50 to 200°C for the compositions with 0.03⩽ x ⩽0.09. A change from a normal ferroelectric behavior to diffusive and dispersive relaxor-like characteristic was also observed. Moreover, (1− x)BT–xBZZ ceramics show good dielectric temperature stability over a wide temperature range, which indicates that these ceramics can be applied in the temperature stability devices. [Copyright &y& Elsevier]

Abstract: Two new tungsten bronze ferroelectrics Sr6−n Pr n Ti n Nb10−n O30 (n =1, 2) were synthesized and characterized. Sr5PrTi3Nb7O30 and Sr4Pr2Ti4Nb6O30 had tetragonal filled tungsten bronze structure at room temperature, and exhibited weak ferroelectric nature with remnant polarizations (P r ) of 0.81 and 0.8μCcm−2, respectively. Sr5PrTi3Nb7O30 showed diffused relaxor behavior with the Curie temperature T c at around 70°C (at 1MHz), while Sr4Pr2Ti4Nb6O30 showed diffused normal ferroelectric transition with T c at 182°C. Their dense ceramics had dielectric constant of 550 and 325, and dielectric loss (tan δ) of 0.05 and 0.006 for Sr5PrTi3Nb7O30 and Sr4Pr2Ti4Nb6O30 at 1MHz, respectively. Heterogeneous mixtures of the two compounds might be used to fabricate temperature-stable dielectrics. [Copyright &y& Elsevier]

• Oxygen content control of LiNi 0.5 Mn 1.5 O 4 was achieved via a microwave annealing treatment; • The prepared non-stoichiometric LiNi 0.5 Mn 1.5 O 4-δ material delivers excellent rate capability; • A solid-solution-like reaction in the prepared LiNi 0.5 Mn 1.5 O 4-δ during cycling was deciphered. The oxygen vacancies are usually beneficial to Li-ion transport in high-voltage spinel LiNi 0.5 Mn 1.5 O 4 (LNMO) cathode material, but the influence of the oxygen deficiencies in the disordered spinel LNMO oxide on phase transition mechanism during charging/discharging remains unknown. Herein, the oxygen stoichiometry control of LNMO was achieved through a microwave annealing treatment. The prepared non-stoichiometric LiNi 0.5 Mn 1.5 O 4-δ (Fd 3 - m) materials delivered a pronounced improvement of rate capability, e.g. the discharge capacity at an ultra-fast rate (10 C) is up to 104.3 mA h g−1. Instead of the typical two-step phase transformation process, a solid-solution-like reaction in the as-synthesized LiNi 0.5 Mn 1.5 O 4-δ (Fd 3 - m) during cycling was deciphered by an in situ synchrotron radiation diffraction analysis. These findings shed light on the phase transition mechanism of defective spinel oxides with an enhanced electrochemical properties. [ABSTRACT FROM AUTHOR]