Pseudo Cubic Research Articles

Strain evolution from the ferroelectric to the relaxor state in (0.67 - x)BiFeO3-0.33BaTiO3-xBi(Mg0.5Zr0.5)O3 lead-free ceramics.

The BiFeO3-BaTiO3 solid solution exhibits enhanced electric properties due to its modified phase structure with relaxor characteristics and reduced leakage current. Despite these advancements, the underlying mechanism behind the phase transition from a ferroelectric to a relaxor state in BF-BT ceramics remains largely unexplored. Here, the evolution of strain in (0.67 - x)BiFeO3-0.33BaTiO3-xBi(Mg0.5Zr0.5)O3 ceramics is investigated, with a focus on the strain transition from a ferroelectric to a relaxor phase. A strengthening of relaxor behavior is observed in the modified rhombohedral (R) and pseudocubic (PC) phase structure, resulting in optimal strain (Suni = 0.25%, Spos = 0.24%) at x = 0.04. The enhanced strain is attributed to the promotion of domain switching and the presence of strong random fields, with polar nanoregions integrating into a long-range ordered matrix. Furthermore, a gradual increase in strain with rising temperature is noted, driven by increased polarization and the expansion of ferroelectric domains. This study underscores the critical role of structural modifications in augmenting the electric response of BF-BT ceramics, thereby advancing the development of lead-free piezoelectric materials.

The phase composition, dielectric, and energy storage performance of A-site vacancy modulated BaTiO3 ceramics with Bi(In1/2(Li0.5Ta0.5)1/2)O3 modification

The (1-x)Ba0.94Ce0.04TiO3-xBi(In1/2(Li0.5Ta0.5)1/2)O3 (BCT-BILT) relaxor ferroelectric ceramic system was explored based on the A-site vacancy design and defect dipole engineering. The impacts of different doping concentrations on the phase composition, dielectric and energy storage performance of the BCT-BILT ceramics were studied and discussed in detail. The pure BCT and 0.95BCT-0.05BILT samples exhibited a mixed crystal structure of tetragonal (T) and pseudo-cubic (PC) phase, while the BCT-BILT samples with x > 0.05 possessed a cubic (C) phase, accompanied by the secondary phases of BaBi2Ta2O9 and BaTa2O6. With an increase in the BILT doping concentration, the surface morphologies of the ceramics were continuously modulated, and the dielectric loss had been reduced to 0.001 at 1 kHz, which was beneficial to improve the energy storage properties. Compared to the pure BCT, the breakdown field strength was significantly enhanced owing to the formation of Aurivillius phase BaBi2Ta2O9 and the increased dielectric relaxation. Ultimately, the highest energy storage density of Wrec = 0.7 J/cm3 and high energy conversion efficiency of η = 95 % was realized at the composition of x = 0.05 under a small electric field of 130 kV/cm. Furthermore, the good temperature stability with the ΔWrec/Wrec30°C < 9 % and Δη/η30°C < 6.5 % was acquired for the samples with x = 0.20–0.30 in the temperature range of 30–120 °C, owing to the synergistic roles of the defect dipoles, impurities BaBi2Ta2O9, and polar nanoregions (PNRs). The 0.95BCT-0.05BILT ceramic obtains discharge energy density Wdis of 0.35 J/cm3 and fast discharge speed t0.9 of 312 ns at 60 kV/cm, current density CD of 255.4 A/cm2 and power density PD of 10.2 MW/cm3 at 80 kV/cm. This work is of guiding significance for designing and optimizing energy storage performance of lead-free relaxors from the perspective of defect building and engineering.

Investigation of the structural and piezoelectric characteristics of (1-x)Pb(Zr, Ti)O3-xPb(Zn0.4Ni0.6)1/3Nb2/3O3 ceramics with R-PC-T multistructure

The structural and various electrical properties of (1-x)Pb(Zr1-zTiz)O3-xPb(Zn0.4Ni0.6)1/3Nb2/3O3 [(1-x)P(Z1-zTz)-xPZNN] piezoceramics have been systematically investigated to ascertain the compositions that manifest a rhombohedral-pseudocubic-tetragonal (R-PC-T) multistructure. Rietveld refinement results indicate that the pseudocubic (PC) structure observed in the (1-x)P(Z1-zTz)-xPZNN piezoceramics closely resembles the Pm3m cubic structure. Nonetheless, the PC structure cannot be classified as cubic, given that piezoceramics exhibiting the PC structure also demonstrate ferroelectric and piezoelectric properties. The R-PC-T multistructure was detected in (1-x)P(Z1-zTz)-xPZNN piezoceramics for compositions where 0.335 ≤ x ≤ 0.44, across various z values. Compositions exhibiting the R-PC-T multistructure are identified as particularly promising. Notably, the piezoceramic with the composition 0.58 P(Z0.41T0.59)-0.42PZNN (x = 0.42 and z = 0.59) displayed remarkable piezoelectric properties, including a high piezoelectric charge constant, d33, of 825 pC/N, a coupling coefficient, kp, of 0.7, and a strain of 0.185% at 3.0 kV/mm, alongside a high Curie temperature (TC) of 240 °C.

Understanding the structural mechanism of electric properties in xBiFeO3-(1-x)BaTiO3 lead-free piezoelectric solid solutions

Chemical distributions, local phase and domain configurations of xBiFeO3-(1-x)BaTiO3 (BF-BT) ceramics with different macroscopic phases were carefully studied to understand the structural mechanisms of electric properties. Universal BF-rich@BT-rich@average-composition triple core-rim structures were found to exist in all the compositions, and the volume fractions of cores decrease with the BF content. The inner cores all show dominant rhombohedral (R) phase, while the rims change from dominant pseudo-cubic (PC) phase with polymorphic polar nanoregions (PNRs) (x = 0.64) to coexistence of R and PC with PNRs and nanodomain (x = 0.7) and then to dominant R phase with PNRs+macrodomain (x = 0.75). The high densities of phase and domain boundaries are responsible for the high and thermal-stable electric-field induced strain in the PC phase. Our results evidence the decisive contribution of the composition-modulated hierarchical microstructures to the electric-field induced strain, and are anticipated to provide the necessary foundation for the effective modulation of the piezoelectricity.

Structure characters, and thermal evolution of electrical and elastic behaviors in xBi(Ni1/2Hf1/2)O3-(1−x)PbTiO3 solid solutions with a tetragonal-pseudocubic phase boundary

In this study, we synthesized solid solutions of xBi(Ni1/2Hf1/2)O3-(1 − x)PbTiO3 (xBNH-PT) with the aim of elucidating their phase boundary behaviors and the associated physical properties. A tetragonal (T) - pseudocubic (PC) phase boundary was confirmed at x = 0.38. For x = 0.36 and x = 0.37 with distinct tetragonal distortions, a spontaneous ferroelectric-relaxor transition was observed. The introduction of a T-PC phase boundary not only led to enhanced piezoelectric properties (d33 = 456 pC/N, x = 0.39) but also effectively suppressed the spontaneous ferroelectric-relaxor transition. Detailed analysis revealed that the local structure of the initial state in 0.39BNH-0.61PT remained tetragonal. After poling, a long-range tetragonal phase was formed from the short-range tetragonal clusters, with the c/a value of ∼1.01. Our observations of frequency dispersion strongly suggest the presence of local inhomogeneities, resulting in distinct poling effects on the dielectric and elastic behaviors of the material.

Enhanced energy storage efficiency and temperature stability of Li2CO3-assisted BST-based ceramics by optimizing B-site dopants

In this work, 5 wt‰ Li2CO3-doped 0.88Ba0.8Sr0.2TiO3-0.12BiMeO3 (BST-BMe+5‰Li2CO3, Me = Al3+, Ga3+, Ta5+, and In3+) ceramics were fabricated using solid phase sintering approach. The impacts of different B-site Me ions on the crystalline structure, permittivity stability, energy density, and energy storage efficiency of these ceramics were studied. The XRD results revealed that the mixed tetragonal (T) and pseudo cubic (pC) phase structure was obtained for all the samples. The In/5‰Li2CO3 sample exhibits the optimal energy density of Wrec = 1.04 J/cm3 and the energy efficiency of η = 96% at 170 kV/cm. Meanwhile, the sample shows outstanding temperature stability satisfying the EIA-X8R criteria, which is ascribed to the combined roles of defect dipoles and large lattice distortion. Li2CO3 plays a key role in reducing the sintering temperature, raising the breakdown strength, enhancing the relaxation characteristics, and improving the thermal stability of energy efficiency of the ceramics.

Excellent piezoelectric performance of BiFeO3–BaTiO3– La(Mg2/3Nb1/3)O3 lead-free ceramics via relaxation regulation near the morphotropic phase boundary

Although BiFeO3–BaTiO3-based lead-free ceramics have attracted much attention in recent years as a high temperature piezoelectrics, their d33 value is still difficult to exceed 200 pC/N through conventional methods. In this work, a novel (0.7-x)BiFeO3-0.3BaTiO3-xLa(Mg2/3Nb1/3)O3 (x = 0–0.005) ternary system was reported to own excellent room-temperature piezoelectric constant (d33) ∼216 pC/N and high Curie temperature (480 °C) at x = 0.003 simultaneously. It reveals that the compositions undergo an obvious phase transition from ferroelectric (FE) rhombohedral (R) phase to relaxor pseudo-cubic (PC) phase via an R–PC morphotropic phase boundary (MPB). More importantly, piezoelectric nonlinear Rayleigh analysis and S-E/P-E curves suggest that the significantly enhanced domain dynamics due to the coexistence of macrodomain and nanodomain can be observed in the x = 0.003 sample. The synergy of these two effects induce the improved d33 value observed in the x = 0.003 sample. In addition, the compositions exhibit the inhibition of defect dipoles and the improvement of the high temperature resistivity, leading to the excellent thermal stability with sensitivity coefficients ƞ less than ± 5% in the annealing temperature range of 25–400 °C. The present work provides a guideline for the subsequent design of high-temperature lead-free ceramics.

Improved epitaxial growth and multiferroic properties of Bi3Fe2Mn2Ox using CeO2 re-seeding layers.

In ferroelectric and multiferroic-based devices, it is often necessary to grow thicker films for enhanced properties. For certain phases that rely on substrate strain for growth, such thicker film growths beyond the typical thin film regime could be challenging. As an example, the Bi3Fe2Mn2Ox (BFMO) Aurivillius supercell (SC) phase possesses highly desirable multiferroic (i.e., ferromagnetic and ferroelectric) properties and a unique layered structure but relies heavily on substrate strain. Beyond the thin film regime (approximately 100 nm), a less desirable pseudo-cubic (PC) phase is formed. In this work, a novel heterogeneous re-seeding method is applied to maintain the strained growth in this SC phase beyond the thin film regime, thus enabling the growth of thick BFMO SC phase films. The insertion of periodic CeO2 interlayers reintroduces the heteroepitaxial strain and effectively re-initiates the growth of the SC phase. The thick BFMO SC phase maintains the overall multiferroic and interesting anisotropic optical properties, even exceeding those of the typical 100 nm SC film. This re-seeding method can be effectively adopted with other SC systems or strain-dependent thin films, thus introducing practical applications of the new SC phases without thickness limitations.

TiO2/β-C3N4 for sunlight-driven overall water splitting

β-C 3 N 4 is one of the most difficult phases to synthesize among the C 3 N 4 structures (α, β, cubic, pseudo cubic, and graphitic), and it has attracted marked attention because of its unique super hardness, optical properties, low density, good chemical resistance, and thermal stability. In this paper, a uniform β-C 3 N 4 layer is successfully prepared and coated on a TiO 2 nanotube substrate via a calcination treatment using ethylenediamine as the carbon nitride precursor. The as-obtained TiO 2 /C 3 N 4 exhibites a promising sunlight-driven overall water splitting ability, with 1026.7 μmol H2 g cat. −1 h −1 and a 446.4 μmol O2 g cat. −1 h −1 generation rates simultaneously realized. Importantly, the turnover frequency for O 2 in the photocatalytic splitting process reaches up to 4472.8 h −1 for the overall water splitting process, which is ~77.6 times that of the single β-C 3 N 4 system (57.6 h −1 ) for O 2 generation. In-situ Raman investigation demonstrates that N vacancy defects in β-C 3 N 4 served as the active site for O 2 generation from H 2 O, which is a hard nut to crack for C 3 N 4 all the time. • β-C 3 N 4 has been successfully prepared and coated on TiO 2 nanotubes under ambient pressure. • The photocatalyst has outstanding overall water decomposition activity. • This work proved that the N vacancy defect in β-C 3 N 4 is the active site for O 2 generation by in-situ Raman examination.

The evolution of structure and electrical properties for BiFeO3–PbTiO3–Ba(Zr0.3Ti0.7)O3 high-temperature piezoceramics near the morphotropic phase boundary

The development of piezoceramics with high Curie temperature and high piezoelectrical performance has always been a long-cherished goal for many researchers. In this work, we have fabricated 0.55BiFeO3-(0.45-x)PbTiO3-xBa(Zr0.3Ti0.7)O3 ternary ceramics near the morphotropic phase boundary (MPB) by conventional solid-state method. XRD patterns indicate that there is an evolution from the tetragonal (T) to pseudo-cubic (PC) phase with BZT content increasing from 0.125 to 0.225. Also, the slim P-E loop transforms into a saturated shape with the decrease of coercive field Ec. Piezoresponse force microscope (PFM) analysis reveals that when x (BZT content) increases, domain density increases. The optimum piezoelectric coefficient d33 (~220 pC/N) is obtained at x = 0.175, while Curie temperature TC and dielectric loss tanδ are 434 °C and 0.019, respectively. These results show that BF-PT-based piezoceramics are competitive candidates in future high-temperature applications of piezoelectric ceramics.

Modelling the structural variation of quartz and germanium dioxide with temperature by means of transformed crystallographic data.

The pseudocubic (PC) parameterization of O4 tetrahedra [Reifenberg & Thomas (2018). Acta Cryst. B74, 165-181] is applied to quartz (SiO2) and its structural analogue germanium dioxide (GeO2). In α-quartz and GeO2, the pseudocubes are defined by three length parameters, aPC, bPC and cPC, together with an angle parameter αPC. In β-quartz, αPC has a fixed value of 90°. For quartz, the temperature evolution of parameters for the pseudocubes and the silicon ion network is established by reference to the structural refinements of Antao [Acta Cryst. (2016), B72, 249-262]. In α-quartz, the curve-fitting employed to express the non-linear temperature dependence of pseudocubic length and Si parameters exploits the model of a first-order Landau phase transition utilized by Grimm & Dorner [J. Phys. Chem. Solids (1975), 36, 407-413]. Since values of tetrahedral tilt angles about ⟨100⟩ axes also result from the pseudocubic transformation, a curve for the observed non-monotonic variation of αPC with temperature can also be fitted. Reverse transformation of curve-derived values of [Si+PC] parameters to crystallographic parameters a, c, xSi, xO, yO and zO at interpolated or extrapolated temperatures is demonstrated for α-quartz. A reverse transformation to crystallographic parameters a, c, xO is likewise carried out for β-quartz. This capability corresponds to a method of structure prediction. Support for the applicability of the approach to GeO2 is provided by analysing the structural refinements of Haines et al. [J. Solid State Chem. (2002), 166, 434-441]. An analysis of trends in tetrahedral distortion and tilt angle in α-quartz and GeO2 supports the view that GeO2 is a good model for quartz at high pressure.

In situ poling X-ray diffraction studies of lead-free BiFeO3–SrTiO3 ceramics

The origin of the large electrostrain in BiFeO3-BaTiO3 (BF-BT) ceramics is controversial and has been attributed to either a field-induced transition to a long-range ferroelectric (FE) state or to multi-symmetry, polar nanoregions within a pseudocubic matrix whose vectors approximately align with the direction of the applied field. The (1-x)BiFeO3-xSrTiO3 (BF-xST) solid solution is structurally and microstructurally similar to BF-BT and provides a further case study to assess the origin of electrostrain. In BF-xST, electrostrain is optimized at x = 0.4 (0.15%) which zero field, room temperature full-pattern X-ray diffraction (XRD) Rietveld refinement and scanning/transmission electron microscopy suggest is composed of 15% rhombohedral (R) cores, surrounded by 85% pseudocubic (PC) shells. In-situ poling synchrotron XRD reveals that all peaks remain singlet and exhibit no change in full width half maximum up to 100 kV cm−1, confirming the absence of long-range FE order and the retention of short-range polar order, despite the large applied field. Strain anisotropy (calculated from individual peaks) of ε220 > ε111 > ε200 and the associated strain orientation distribution however, indicate the existence of local orthorhombic (O), R and tetragonal (T) symmetries. The data therefore imply the existence under poling of multi-symmetry polar nanoregions in BF-0.4ST rather than a long FE phase, supporting the model described by Wang and co-workers (2019) for BF-BT compositions.

The effects of crystal structure on the photovoltaic performance of perovskite solar cells under ambient indoor illumination

Organic-inorganic hybrid lead halide perovskite materials with the general formula MAPbI3-nBrn (n = 0, 1, 2, and 3) exhibiting a range of crystal structures and a wide range of optical bandgaps are explored for their potential to harvest energy from ambient light sources. The replacement of I− with Br− is found to transform the perovskite crystal structure from the tetragonal for MAPbI3 to the pseudo cubic for MAPbI2Br and MAPbIBr2 and cubic for MAPbBr3 while increasing the optical bandgap from 1.59 eV to 2.31 eV. Photovoltaic cells (PVCs) are constructed using these perovskites and are found to exhibit power conversion efficiencies (PCEs) of 29.83 (MAPbI3), 23.75 (MAPbI2Br), 21.47 (MAPbIBr2), and 19.94% (MAPbBr3) under LED light illumination (1000 lux; ~0.371 mW cm−2), with a record high open-circuit voltage (VOC) of 1.15 V being observed for the MAPbBr3. The effect of crystal structure variation on the charge carrier mobility, trap states, recombination losses, photovoltaic properties, and operational stabilities has been investigated systematically under indoor illumination. Overall, this work provides a clear vision on the influence of perovskite crystal structures upon the photovoltaic properties and shows a pathway to achieve high VOC in perovskite PVCs under low-intensity ambient light sources.

Low-Temperature Synthesis of K–Ba–Bi–O Oxides in KOH Solution

The reaction of KBiO3–δ with Ba2+ ions at a Ba : Bi ratio of 0.5‒1.6 (mol.) in a 10 M. KOH solution under reflux (~140°C) has furnished oxides, which composition and structure have been studied by X-ray diffraction, energy dispersive X-Ray, and chemical analysis. Pseudo cubic (а = 4.271‒4.285 A) perovskite-like phases of barium‒bismuth(III,V)‒potassium oxides with insignificant impurity of sodium have been formed in the KBiO3–δ‒Ba2+‒OH–‒H2O system during 1 h. The products have been characterized by an average oxidation state of bismuth –Bi = 4.36‒4.59. Barium content in the resulting oxides has increased with an increase in its concentration in the charge. According to the Ba–Bi ratio, the resulting phases can be classified as non-superconducting oxides of homologous series МxBamBim+nOy (x <n), МxBamBim+nOy, and (М, Ba)m+nBimOy (m = 1, 2, ...; n = 0, 1, 2, ...), M = K, Na.

Unravelling the sintering temperature-induced phase transformations in Ba(Fe0.7Ta0.3)O3-δ ceramics

Our work reports on the fundamental details of the crystal structure and phase transformations in Ba(Fe0.7Ta0.3)O3-δ, the best known temperature-independent oxygen-sensing ceramic material for applications in extreme environments. Ba(Fe0.7Ta0.3)O3-δ ceramics were synthesized using conventional solid-state ceramic reaction under variable sintering temperatures (Ts = 1200–1350 °C). Combined X-ray diffraction (XRD) and high-resolution transmission electron microscopy (TEM) measurements revealed the Ts-induced phase transformations and their origin in Ba(Fe0.7Ta0.3)O3-δ. Associated with phase transformations, pseudo-cubic (PC) reflections, such as {200}PC, {211}PC, and {220}PC, exhibited distinct anomalies with increasing Ts. At Ts = 1200 °C, Ba(Fe0.7Ta0.3)O3-δ stabilized in mixed orthorhombic + rhombohedral phases (Amm2 + R3m). With increasing Ts (≥1250 °C), Ba(Fe0.7Ta0.3)O3-δ ceramics stabilized in tetragonal/rhombohedral [P4mm + R3m] mixed phases, while variations in the quantity of the respective phases were observed. Because both structure and crystal chemistry play key roles in achieving enhanced performance in chemical sensing and catalytic converters, detailed understanding of the phase transformations and crystal structure of Ba(Fe0.7Ta0.3)O3-δ ceramics, as derived in this work, will be useful to develop chemical sensors with optimum performance for high-temperature and corrosive environments.

Phase transition, ferroelectric and piezoelectric properties of B-site complex cations (Fe0.5Nb0.5)4+-modified Ba0.70Ca0.30TiO3 ceramics

Ba0.70Ca0.30Ti1-x (Nb0.5Fe0.5)xO3 lead-free ceramics (abbreviated as BCTNFx, x = 0–0.12) were prepared by solid-state reaction method. The influence of B-site (Fe0.5Nb0.5)4+ substitution on phase structure, microstructure, dielectric, ferroelectric and piezoelectric properties of Ba0.70Ca0.30TiO3 ceramics were systematically studied. The BCTNFx ceramics consist of diphasic tetragonal (T) and orthorhombic (O) phases at x = 0–0.04, pseudocubic (PC) and O phases at x = 0.05–0.08, cubic (C) and O phases at 0.08 < x ≤ 0.12. Increase of (Fe0.5Nb0.5)4+ doping improves sinterability, depresses the ferroelectric - paraelectric phase transition temperature (Tm) monotonically from 128 °C at x = 0 to -86 °C at x = 0.12, induces enhanced relaxor behavior and weakens piezoelectric properties. The room temperature relative dielectric constant (εr) and dielectric loss tangent (tanδ) increase with increasing x and reach the maximum values of 4869 and 0.06 respectively at x = 0.06. Whereas the average grain size (abbreviated as AGS), ferroelectric properties and electric field induced strain increase significantly by introducing 2.0 mol% B-site complex cations (Fe0.5Nb0.5)4+ into Ba0.70Ca0.30TiO3 ceramics. The BCTNF0.02 ceramics achieve optimal electrical properties with εr = 1268, tan δ = 0.03, Tm = 102 °C, Pmax = 12.8 μC/cm2, Pr = 6.1 μC/cm2, EC = 6.0 kV/cm, d33 = 117 pC/N, kp% = 0.18%, Qm = 236, bipolar Smax% = 0.20%, unipolar Smax% = 0.16% and d33∗ = 314 pm/V. The variation of electrical properties of BCTNFx ceramics is attributed to the combined action of grain size effect, phase transition, weakness of octahedral distortion, clamping effects of the internal bias electric field Ei on domain wall motion induced by B-site cations (Fe0.5Nb0.5)4+ displacement.

Excellent thermal stability and aging behaviors in BiFeO3‐BaTiO3 piezoelectric ceramics with rhombohedral phase

AbstractBiFeO3‐BaTiO3 (BF‐BT) solid solutions are lead‐free candidates for high‐temperature piezoelectric applications. BF‐BT ceramics with compositions near the morphotropic phase boundary (MPB) separating rhombohedral (R) and pseudo‐cubic (PC) phases were fabricated by the conventional high temperature sintering method, and their thermal stability and aging properties were studied in detail. BF‐BT ceramics with rhombohedral (R) phase show much better thermal stability and aging properties than those with pseudo‐cubic (PC) or coexistence of PC and R phases. The thermal degradation and aging rates of BF‐BT ceramics with R phase are on the order of 1% and 1.2% per decade, respectively. X‐ray diffraction results reveal that the domain state of poled rhombohedral BF‐BT ceramics is stable up to its Curie temperature, which is responsible for the high thermal stability. The Rayleigh analysis shows that the low aging rate is attributed to the low domain wall contribution to the overall piezoelectric response. The high thermal stability and low aging rates indicate that the lead‐free BF‐BT ceramics with R phase are potential candidates for sensor and transducer applications over a broad temperature range.

Phase evolution, microstructure, electric properties of (Ba1-xBi0.67xNa0.33x)(Ti1-xBi0.33xSn0.67x)O3 ceramics

(Ba1-xBi0.67xNa0.33x)(Ti1-xBi0.33xSn0.67x)O3 (abbreviated as BBNTBS, 0.02 ⩽ x ⩽ 0.12) ceramics were fabricated via a traditional solid state reaction method. The phase transition of BBNTBS from tetragonal to pseudo cubic is demonstrated by XRD and Raman spectra. The BBNTBS (x = 0.1) ceramics have decent properties with a high εr (~2250), small Δε/ε25°C values of ±15% over a wide temperature range from -58 to 171 °C, and low tanδ ⩽ 0.02 from 10 to 200 °C. The basic mechanisms of conduction and relaxation processes in the high temperature region were thermal activation, and oxygen vacancies might be the ionic charge transport carriers. Meanwhile, BBNTBS (x = 0.1) exhibited decent energy storage density (Jd = 0.58 J/cm3) and excellent thermal stability (the variation of Jd is less than 3% in the temperature range of 25–120 °C), which could be a potential candidate for high energy density capacitors.

Enhancement of ferromagnetism by suppression of spiral spin structure in Ba doped BiFeO3

Abstract Polycrystalline samples with formula Bi1−xBaxFeO3 (x = 0.0–0.25) were fabricate by solid state reaction technique. Synchrotron XRD diffraction confirmed that the rhombohedral structure is transformed to pseudo cubic. The Mossbauer spectra inferred the existence of only Fe3+ ions, these results also indicated the destruction of spiral spin structure with increasing Ba doping level. The magnetic measurements showed that the coercive field is increased from 22.4 to 2600.2 Oe and the remnant magnetization is increased from 0.67 μemu/g to 0.49 emu/g on increasing Ba concentration. This increase in ferromagnetism can be attributed to the destruction of spiral spin structure, which is indicated from the Synchrotron XRD and Mossbauer results.

Lead-free 0.7BiFeO3-0.3BaTiO3 high-temperature piezoelectric ceramics: Nano-BaTiO3 raw powder leading to a distinct reaction path and enhanced electrical properties

Herein, nano-BaTiO3/Bi2O3/Fe2O3 and BaCO3/TiO2/Bi2O3/Fe2O3 were respectively used to prepare 0.7BiFeO3-0.3BaTiO3 (0.7BF-0.3BT) ceramics by conventional solid-state method and clarify the reaction path, phase structure, microstructure, ferroelectric, and piezoelectric properties. 0.7BF-0.3BT ceramic using nano-BaTiO3 with cubic phase (CBT) undergoes the formation of rhombohedral α-phase (Rα) and the transition from Rα and CBT to rhombohedral β-phase (Rβ) and pseudo-cubic (PC) phases, while the counterpart using BaCO3/TiO2 directly generates Rβ and PC. Nano-BaTiO3 can decrease pores and oxygen vacancies in the resultant ceramics comparing to BaCO3/TiO2, which is due to an inhibited decomposition of Rα and a weaker reduction of Fe3+ to Fe2+, leading to increased density and reduced leakage current density. Benefitting from a proper phase ratio, increased density and reduced leakage current density, the enhanced piezoelectric properties d33 = 210 pC/N, kp = 0.34, Pr = 31.2 μC/cm2 and TC = 514 °C are obtained in 0.7BF-0.3BT ceramic using nano-BaTiO3. Our work reveals the importance of raw materials and the potential of BF-BT as a high-temperature lead-free piezoelectric ceramic material.