Polarization-electric Field Loops Research Articles

Polarization stability and its influence on electrocaloric effects of high entropy perovskite oxide films

In principle, the configurational entropy inherent in High Entropy Oxides (HEOs) could facilitate large electrocaloric effects (ECE) by promoting polar entropy. In this study, it is demonstrated that the time stability of the remanent polarization can be tuned via B-site disorder in High Entropy Perovskite Oxides (HEPO) films. Eight HEPO powders were synthesized; the propensity for perovskite phase formation was consistent with the Goldschmidt tolerance factor. While entropic contributions stabilize HEPO, they do not fully predict the stabilization. Relative dielectric permittivities between 2000 and 600 can be achieved for the B-site disordered HEPO films with loss tangents below 6 % at room temperature. All films showed similar polarization-electric field loops with maximum polarization up to 48 μC cm−2 and a remanent polarization ≥ 20 μC cm−2 measured at room temperature with applied electric field of 1100 kV cm−1 at a frequency of 10 kHz. The temperature of the dielectric maximum (Tmax) increased from 105 °C to 225 °C with increasing average ion size on the B-site. Polarization stability of the HEPO films was investigated using Positive-Up-Negative-Down (PUND) measurements. It was found that in some HEPO films, 24 % of the remanent polarization decayed within 2 s. By employing the time stability of the remanent polarization, enhanced electrocaloric effects of HEPO film was predicted to be 14.9 K and 11.5 J Kg−1K−1 at an applied field of 1120 kV cm−1, for electrocaloric temperature change and entropy change, respectively.

Synergetic effect of hexaferrite and reduced graphene oxide (rGO) in photothermal therapy and hyperthermia applications

This research article describes the synthesis of composite materials by combining T-type hexagonal ferrite and reduced Graphene Oxide using the standard ceramic process. The Calcium-based T-type hexagonal ferrite was synthesized by using the sol-gel auto-combustion method while the reduced graphene oxide by adopting the Hummer method. The crystallite size varied in the range of 23.38 -39.16 nm as calculated from the X-ray diffraction (XRD) data. Consequently, the lattice parameters 'a' and 'c' decreased from 5.9 to 5.1 Å and from 29.92 to 28.32 Å, respectively. The use of atomic force microscopy (AFM) revealed a range of particle sizes at the surface, varying from 1.70 nm to 3.85 nm. Moreover, the saturation and remanence magnetization values demonstrated an increasing trend with T-type hexaferrites concentration whereas the coercivity decreased. The UV–vis near-infrared spectra exhibited substantial light absorption, characterized by a wide absorption range in the visible and near-infrared (NIR) region (700–1100 nm) which indicates its use in Photothermal therapy (PTT). The Calcium T- type hexaferrite exhibited clear peaks in the blue, green, violet, and yellow spectra in its photoluminescence (PL) properties. These peaks are believed to be caused by oxygen vacancies and defects. The synthesized samples displayed a lossy behavior in the polarization-electric field (P-E) loop, with saturation polarization levels exceeding remnant polarization, which is an amenable condition for lossy behavior. Most importantly, the synthesized materials had significant thermal responses when exposed to an alternation (AC) magnetic field, indicating their potential use in magnetic hyperthermia applications.

High energy density and energy efficiency in AgNbO3-based multilayer ceramic capacitors induced by coexisted antiferroelectric and paraelectric phases

AgNbO3-based lead-free antiferroelectric materials have been attracted increasing attention due to their excellent energy storage performance. But most of the AgNbO3-based ceramics still suffer from low energy efficiency. Herein, coexisted antiferroelectric phase and paraelectric phase are realized in La-doped AgNbO3-based multilayer ceramic capacitors at room temperature, which resulted in slim polarisation-electric field loops with hysteresis-free and high breakdown strength over 1000 kV/cm. Both the hysteresis-free polarisation-electric field loops and high breakdown strength are beneficial for the energy storage density and energy efficiency. In (Ag0.64La0.12)NbO3 multilayer ceramic capacitors, a high breakdown strength of 1060 kV/cm was attained, which contributes to a recoverable energy storage density (Wrec) of 9.1 J/cm3 and an energy efficiency (η) of 95.8%. Furthermore, the Wrec and η remains above 7.5 J/cm3 and above 83% in the temperature range of 30 °C–130 °C under 1000 kV/cm, and remains above 4.8 J/cm3 and above 91% in the frequency range of 1–100 Hz under 700 kV/cm. This work provides a feasible method for preparing AgNbO3-based ceramics with high energy storage performance.

Ultrahigh Energy Storage in (Ag,Sm)(Nb,Ta)O3 Ceramics with a Stable Antiferroelectric Phase, Low Domain-Switching Barriers, and a High Breakdown Strength.

AgNbO3 (AN) antiferroelectrics (AFEs) are regarded as a promising candidate for high-property dielectric capacitors on account of their high maximum polarization, double polarization-electric field (P-E) loop characteristics, and environmental friendliness. However, high remnant polarization (Pr) and large polarization hysteresis loss from room-temperature ferrielectric behavior of AN and low breakdown strength (Eb) cause small recoverable energy density (Wrec) and efficiency (η). To solve these issues, herein, we have designed Sm3+ and Ta5+ co-doped AgNbO3. The addition of Sm3+ and Ta5+ reduces the tolerance factor, polarizability of B-site cations, and domain-switching barriers, enhancing AFE phase stability and decreasing hysteresis loss. Meanwhile, adding Sm3+ and Ta5+ leads to decreased grain sizes, increased band gap, and reduced leakage current, all contributing to increased Eb. As a benefit from the above synergistic effects, a high Wrec of 7.24 J/cm3, η of 72.55%, power density of 173.73 MW/cm3, and quick discharge rate of 18.4 ns, surpassing those of many lead-free ceramics, are obtained in the (Ag0.91Sm0.03)(Nb0.85Ta0.15)O3 ceramic. Finite element simulations for the breakdown path and transmission electron microscopy measurements of domains verify the rationality of the design strategy.

Multiple Phase Structures and Enhanced Dielectric Properties of Side-Chain Liquid Crystalline Polymer Containing Unique Biaxial Mesogen with Large Dipole Moment

To achieve all-organic polymer with high dielectric performances, we have designed a novel side-chain liquid crystalline polymer (P7) with strong polar mesogen of (Z)-4-(2-cyano-2-phenylvinyl)benzonitrile (CSCN) attached to polycyclooctene backbone. The bis-cyano-substituted CSCN is board-shaped and exhibits a large dipole moment (8.54 D) which tilts ∼34.2° away from its molecular long axis. Consequently, CSCN shows unique dual molecular anisotropy: one from biaxial shape anisotropy and the other from polarization anisotropy. The complex phase behaviors of P7 were investigated employing mainly the techniques of differential scanning calorimetry and X-ray diffraction. Four liquid crystal (LC) phases are identified as K0, K1, K2 and K3, which are SmA, highly-ordered biaxial SmA, B5-like and B7-like, respectively, with the thermal stability increased in sequence. The experimental results indicate that the different LC phases are arisen from the competition and balance between π-π stacking and dipole-dipole interaction. While the face-to-face π-π stacking is dominant in K0 and K1, optimizing the dipole-dipole interaction causes the CSCN mesogens within the smectic layer to tilt and rotate, resulting in K2 and K3. We further investigated the dielectric properties of P7 films using polarization-electric field loops test. The dielectric constant (εr) of P7 is found to be LC structure dependent, which is increased when the LC phase is varied from K0 to K3. With an average εr of 9.7 achieved in K3 and the low dielectric loss (tan δ = 0.001), P7 film offers a promising material in advanced applications like energy storage and electronic devices.

Significantly enhanced electrocaloric effect by composition modulation in lead-free BaTiO3-based ceramics

The electrocaloric effect (ECE) offers a pathway to environmentally sustainable and easily miniaturized refrigeration technology, positioning it as a front-runner for the next generation of solid-state cooling solutions. This research unveils a remarkable ECE in a finely tuned (Ba0.86Ca0.14)0.98La0.02Ti0.92Sn0.08O3 ceramic, exhibiting a temperature shift (ΔT) of 1.6 K across more than 85% of the maximum ΔT (ΔTmax) and spanning an exceptionally wide operational range of 92 K. Our investigation on dielectric responses and ferroelectric polarization-electric field (P–E) loops suggests that the broad operational scope results from the fragmentation of extended ferroelectric domains into smaller domains and polar nano-regions (PNRs) supported by PFM analysis. Furthermore, the introduction of La enhances spontaneous polarization by significantly extending the maximum electric field that can be applied, facilitating high-performance ECE at ambient temperature. This study positions BaTiO3-based lead-free ceramic as a sustainable alternative for addressing the cooling demands of modern electronic components, marking a significant stride toward next-generation solid-state refrigeration.

Structural phase coexistence enhances the energy storage density of (Bi0.5Na0.5)0.8Ba0.2Ti1-ySnyO3 lead-free ceramics

In the present study, BaSnO3 was introduced into polycrystalline NBT-BT ferroelectric ceramics and conducted a comprehensive investigation into the structural, dielectric, ferroelectric, and energy storage characteristics of the (Bi0.5Na0.5)0.8Ba0.2Ti1-ySnyO3 (BNBTS) ceramics. The coexistence of structural phases P4mm and Amm2 was observed through Rietveld refinement and also confirmed by Raman analysis. The formation energy decreases with an increase in substitution concentration favouring the formation of the orthorhombic phase. The SEM analysis revealed a denser microstructure characterised by smaller grain sizes, which favourably enhances energy storage density. Furthermore, Raman spectroscopic analysis unveiled a softening of Ti–O bonds, indicating the emergence of macroscopic relaxor behaviour. Dielectric studies provided evidence of a transition from ferroelectric to relaxor behaviour, an observation further confirmed by P-E loop measurements. This transition can be linked to the partial substitution of Sn4+ ions for Ti4+ ions, disrupting the ferroelectric long-range order within the matrix phase. Notably, the polarization-electric field (P-E) loop of BNBTS2 ceramics exhibited a substantial value of polarization (Ps) 30 μC/cm2 with a reduced value of remnant polarization (Pr) 2.29 μC/cm2. These characteristics contributed to the achievement of higher energy recovery (Wrec) and lower energy loss (Wloss) values, measuring 1.184 J/cm3 and 0.142 J/cm3, respectively, with a notable efficiency of 88.8%. Consequently, the system of ternary ceramics demonstrates promise as a potential option for energy storage ceramics among NBT-BT-based materials.

Structural and ferroelectric properties (1-x)(Ba0.9Sr0.1)TiO3-xBi(Mg2/3Nb1/3)O3 lead-free ceramics with remarkable energy storage performance

In this research, (1-x)(Ba0.9Sr0.1)TiO3-xBi(Mg2/3Nb1/3)O3 (BST-BMN, where x = 0, 0.06, 0.08, 0.12 and 0.20) powders were synthesized via a solid-state reaction method. The corresponding lead-free ceramics were obtained at the optimal sintering temperature. For x ? 0.06, the material formed dense, homogeneous pseudocubic perovskite structures. The increase of the BMN content induces strong relaxor behaviours with diffuse phase transition characteristics, enhancing the temperature stability of dielectric properties. Consequently, the ceramics exhibited narrow polarization-electric field (P-E) loops and superior energy storage capabilities. The composition 0.88BST-0.12BMN was found to be optimal, attributed to the improvement in breakdown field strength, yielding a recoverable energy density of 2.504 J/cm3 and an efficiency of 90.2%under an electric field strength of 250 kV/cm. Furthermore, this ceramic composition retains consistent energy storage across temperatures ranging from 20 to 120?C and frequencies from 1 to 100Hz, underscoring its potential for application in high-power pulsed capacitors.

Improved energy storage performance and thermal stability of hafnium-substituted strontium sodium niobate tungsten bronze ceramics.

Dielectric capacitors are widely used in the field of pulsed power systems owing to their ultra-fast charge and discharge capacity; however, considering the complex environment they face in practical applications, how to further improve their thermal stability is an urgent issue that needs to be solved. Tungsten bronzes have the potential to broaden the temperature stability range owing to their unique structure, but only few studies have focused on them. Herein, lead-free Sr4-x La x Na2Hf x Nb10-x O30 ceramics with a tungsten bronze structure were synthesized, and their energy storage properties were comprehensively characterized. With proper Hf substitution in the B site and rare earth substitution in the A site, significantly enhanced relaxor behavior is induced, leading to a broad plateau of the dielectric curve, slim polarization-electric field loop, high energy storage efficiency and stable capacitive performance over a wide temperature range. In addition, an improved microstructure with fewer defects, decreased average grain size, increased band gap and resistance were obtained, which benefit to the increase in breakdown strength and energy storage density. Finally, improved energy storage performance and thermal stability were achieved for the compounds, with W total = 3.6 J cm-3, W rec = 2.9 J cm-3, η = 80% and stable temperature range = 20-160 °C. Thus, the current system is a promising candidate for application in temperature-stable dielectric capacitors.

Structural, Optical, Relaxor and Transport Properties of a Nanocrystalline Double Perovskite: Ba2(FeMo)O6

The paper presents a synthesis (solid-state. reaction) and characterization of a lead-free double perovskite oxide Ba2(FeMo)O6 ceramic. The initial analysis using X-ray diffraction revealed that the material has a cubic crystal symmetry with a micro-lattice strain of 0.000824 and an average crystallite size of 62[Formula: see text]nm. The microstructural features and elemental composition of the prepared polycrystalline sample were examined using scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX). The SEM micrograph, EDX spectrum and elemental mapping show distinctly grown grains with well-defined grain boundaries, purity and distribution pattern of the grains, respectively. Raman scattering spectroscopy is a valuable tool for studying the vibrational modes to get information about structural and chemical properties of materials. The optical properties of the material were investigated using UV–Vis spectroscopy, which provides various parameters including energy bandgap for different technological applications. The electrical behavior of the synthesized double perovskite was examined through frequency- and temperature-dependent dielectric measurements as well as impedance spectroscopy. The electrical conduction in the material followed Jonscher’s power law and is supported by a thermally activated conduction mechanism. The analysis of electrical resistance versus temperature confirms negative temperature coefficient of resistance nature and can be used as NTC thermistors. The study of polarization-electric field loop opens up the possibility of the ferroelectric nature of the studied sample and also measures energy storage density, energy loss density and efficiency for searching different potential applications related to sensors. Overall, the results suggest its potential for various technological applications, such as in sensors and devices requiring specific electrical behavior or ferroelectric properties.

A novel low-loss and high-stability (1-x)Na0.98NbO3–xBi(Al0.5Y0.5)O3 lead-free composite ceramics for dielectric energy storage capacitors

Environmentally friendly, high-performance, lead-free dielectric ceramic capacitors are urgently required for efficient and clean energy storage devices. However, most ferroelectric capacitors require excessively high electric fields to achieve large energy storage densities. In this study, we designed and fabricated a (1-x)Na0.98NbO3–xBi(Al0.5Y0.5)O3 (abbreviated as (1-x)NN-xBAY) composite system with different BAY doping levels using a traditional solid-state reaction method. By introducing 12 mol% BAY into nonstoichiometric NN, the polarization–electric field loop of the 0.88NN–0.12BAY ceramic became significantly slender and showed a superior relaxor behavior. Consequently, a remarkably low dielectric loss of tanδ < 0.005, high energy storage density of ∼ 4.64 J/cm3, and high efficiency of ∼ 85.98 % were simultaneously obtained in the 0.88NN–0.12BAY ceramic under a moderate electric field of 223.47 kV/cm. Furthermore, it exhibited ultrahigh stability in the temperature range of 25–200 °C and wide frequency range of 1–200 Hz, even after 108 electrical cycles. This study demonstrated a promising candidate material for energy storage devices operating under low or medium electric fields.

Analysis of amplitude and frequency-dependent scaling behavior of dynamic hysteresis loop and thermal properties of BaZr0.05Ti0.95O3 ceramic

In this work, single-phase BaZr0.05Ti0.95O3 (BZT) ceramic was prepared through a conventional solid-state reaction route. The structural identity was analyzed by X-ray diffraction (XRD) and Rietveld refinement, which reveals the single-phase perovskite structure of the synthesized sample having an orthorhombic structure and space group Amm2. Scanning electron microscope (SEM) study gives an idea about the well-dense grains with clear grain boundaries of the BZT sample. Frequency and amplitude-dependent Polarization-Electric field (P-E) and Strain-Electric field (S-E) loops were studied. The parameters like remnant polarization (Ec), coercive field (Pr), loop area (<A>), energy storage efficiency (η), field-induced maximum strain (Smax) and inverse piezoelectric coefficient (d33*) were calculated. The scaling behavior of the hysteresis loops area as a function of frequency and field strength is studied. The thermal conductivity and thermal diffusivity as a function of temperature were investigated.

Concentration-driving pinning effect in lead-free Mn-substituted BCZT ferroelectric ceramics

Domain wall motion in ferroelectrics, closely related to electric characteristics and amenable to tuning through doping, remains incompletely understood, particularly with regard to the pinning defect in the (Ba0.85Ca0.15)(Zr0.1Ti0.9)O3 (BCZT) system, which has attracted significant interest. Here, we investigate the defect dipole-assisted pinning effect in Mn-substituted BCZT (abbreviated as BCZT-xMn) ceramics with Mn concentrations ranging from x = 0 to 0.04. As x increases, we observe a gradual decrease in the maximum permittivity, accompanied by a leftward shift in temperature, leading to a diffuse phase transition. Analysis of the dielectric spectrum reveals a consistent trend in the activation energy within a specific concentration range, suggesting the incorporation of oxygen vacancies to maintain electric neutrality. The resulting oxygen vacancies, combined with Mn dopants, form defect dipoles Mn4++e′− VO⋅⋅ −Mn4++e′, attaining sufficient concentration at x = 0.02, and enabling precise establishment of the pinning effect. This phenomenon is extensively documented by the observation of pinched polarization-electric field loops and double current peaks in the current-electric field curves, visually corroborated by experimental data and a 3D phase-field simulation model. Consequently, this study not only elucidates the concentration-driven pinning effect in the BCZT system but also provides valuable insights into doping effects in other lead-free ferroelectrics.

Ferroelectric switching studies in symmetric Ag/Poly(vinylidene fluoride-co-hexafluoropropylene)/Ag capacitor structures

In this article, ferroelectric switching properties of Poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) thin films across symmetric Ag/PVDF-HFP/Ag capacitor structures have been investigated. The structural, microstructural and optical properties of the films are evaluated with grazing incidence X-ray diffraction, Atomic Force Microscopy, and UV visible spectrophotometer. Symmetric quasi-static current-voltage loops exhibit ferroelectric switching, and the corresponding electric displacement- electric field loops show an increase in the coercive field, with the increase in the amplitude of the applied electric field. Higher resistivity of (1.66 – 5.16) × 108 Ω-cm along with optical band gap of 4 eV indicated the good quality of the junctions. Dynamic Polarization-Electric field loops reveal a remnant polarization of 3.22 μC/cm2 and 3.16 μC/cm2 for 80 nm and 160 nm PVDF-HFP films. The increase in coercive field, remnant and saturation polarization parameters with rise in the amplitude of the applied electric fields at 1 Hz for 160 nm PVDF-HFP film are linked to the uniform domain growth phenomena.

Fast polarization switching capability mediated by oxygen deficiency in Co-substituted SrFeO3-δ perovskites

In this study, a series of eco-friendly, oxygen-deficient SrFe1-xCoxO3-δ (x = 0.00, 0.33, 0.66, and 1.00) perovskite samples was prepared via a sol–gel-based auto-combustion route. Analysis of X-ray diffraction data confirmed the synthesis of the single-phase cubic perovskite structure for x = 0.00 to x = 0.66, whereas SrCoO3-δ had a single-phase tetragonal structure. The lattice constants decreased as the Co contents increased due to the smaller ionic radii of Co4+ ions. Field emission scanning electron microscopy images showed that the grain size decreased initially, but the size increased with the increase in Co substitution above x = 0.33. Ferroelectric behavior was analyzed under an electric field of 50 V/cm with a frequency of 50 Hz. The unsaturated polarization–electric field loops for SrFeO3-δ indicated relaxor-type ferroelectric behavior. The maximum polarization (Pmax) and remanent polarization (Pr) both decreased as the Co contents increased. The maximum recoverable energy density was recorded for SrFeO3-δ. However, the maximum energy storage efficiency of 66% was obtained for the SrFe0.67Co0.33O3 sample. These findings demonstrate that members of the SrFe1-xCoxO3-δ series, particularly with x = 0.33, could be potential candidates for use in energy and data storage devices, mainly due to the high value of Pmax − Pr, superior storage efficiency, and rapid polarization switching ability.

Influence of the substituent LiNbO3 in the structural, ferroelectric, dielectric, optical and mechanical properties of K0.5Bi0.5TiO3

Eco-friendly, K0.5Bi0.5TiO3 based binary perovskite system with small amount of LiNbO3 was synthesised and its influence in the structural, ferroelectric, optical and mechanical properties is analyzed. The samples, (1-x)K0.5Bi0.5TiO3-xLiNbO3, named as KLN100x (x = 0.04–0.08) could be refined in both ideal cubic perovskite structure (space group Pm3¯m) and in the tetragonal P4mm structure. The tetragonality of all the samples is close to unity which is common for relaxor ferroelectric perovskites. KLN4, KLN5, KLN6 and KLN7 shows relaxor like polarization-electric field (P-E) loops while highly distorted P-E loop was observed for KLN8. Emergence of impurity phases at higher doping concentrations lead to distorted P-E loop limiting ferroelectric application for higher concentrations. The temperature dependent dielectric curve along with ln(1/εr-1/εm) Vs. ln(T-Tm) plot further confirms the relaxor behavior of the samples. The relaxor nature reduces the energy barrier required for dipole switching in ferroelectric materials resulting in low remanent polarization and enhance the energy storage properties. The recoverable energy density of 1.3 J/cm3 for KLN4 at a low electric field of 100 kV/cm makes it an appealing candidate in the energy storage domain.

Synergistic Optimization of Energy Storage Density of PYN-Based Antiferroelectric Ceramics by Composition Design and Microstructure Engineering.

PbYb0.5 Nb0.5 O3 (PYN)-based ceramics, featured by their ultra-high phase-switching field and low sintering temperature (950°C), are of great potential in exploiting dielectric ceramics with high energy storage density and low preparation cost. However, due to insufficient breakdown strength (BDS), their complete polarization-electric field (P-E) loops are difficult to be obtained. Here, to fully reveal their potential in energy storage, synergistic optimization strategy of composition design with Ba2+ substitution and microstructure engineering via hot-pressing (HP) are adopted in this work. With 2mol% Ba2+ doping, a recoverable energy storage density (Wrec ) of 10.10Jcm-3 and a discharge energy density (Wdis )of 8.51Jcm-3 can be obtained, supporting the superior current density (CD )of 1391.97Acm-2 and the outstanding power density (PD ) of 417.59MWcm-2 . In situ characterization methods are utilized here to reveal the unique movement of the B-site ions of PYN-based ceramics under electric field, which is the key factor of the ultra-high phase-switching field. It is also confirmed that microstructure engineering can refine the grain of ceramics and improve BDS. This work strongly demonstrates the potential of PYN-based ceramics in energy storage field and plays a guiding role in the follow-up research.

Study of the long time relaxation of the weak ferroelectricity in PbZrO3 antiferroelectric thin film using Positive Up Negative Down and First Order Reversal Curves measurements

The weak ferroelectric contribution to the polarization of antiferroelectric lead zirconate (PZO) thin films has been investigated using PUND (Positive Up Negative Down) pulse measurements and hysterons decomposition by First Order Reversal Curves (FORC) technique. The PUND allows decomposing the measured current, obtained from the polarization-electric field loop measurements, into a switching and a non-switching contribution. We show that the weak ferroelectric phase is enhanced when a large electric field has been previously applied to the material, in order to switch from the antiferroelectric to the ferroelectric phase. Using the PUND measurement at fields below the antiferroelectric to ferroelectric phase transition, the polarization loop corresponding only to the ferroelectric switching contribution has been determined revealing that this contribution to the overall polarization is small. FORC measurements, however, indicate that the ferroelectric phase is present at different fields. At low fields, a quite homogeneous distribution of hysterons exists and at large field, a high concentration of hysterons at a field near to the antiferroelectric to ferroelectric phase transition can be seen. Moreover, when changing the delay between pulses of the PUND and the FORC measurements, we show that this weak ferroelectricity contribution is metastable and decreases with time.

Distinct microstructure and property evolution of 0.76(Bi0.5Na0.5)TiO3-0.24SrTiO3 ferroelectric ceramics synthesized with different TiO2 reactants

Single phase 0.76(Bi0.5Na0.5)TiO3–0.24SrTiO3 ferroelectric ceramics have been synthesized with homogenous anatase and hierarchical rutile TiO2 raw reactants (BNST-A and BNST-R). Either calcined powder persists the microstructure characteristics of raw reactants. As the result, when the sintering temperature increases from 1000 to 1200 °C, the average grain size and density of BNST-A increase from 0.49 to 1.48 μm and 5.02 to 5.61 g/cm3, while those of BNST-R from 0.86 to 1.44 μm and 5.37 to 5.61 g/cm3. BNST-A illustrates a predominant ergodic relaxor state, and BNST-R prefers a non-ergodic relaxor state, as evidenced by the distinct polarization-electric field loops and current-electric field curves. Especially, such a distinct ferroelectric state is independent of sintering temperature. It is believed that the special hierarchical microstructure of rutile TiO2 reactant is beneficial to form denser ceramics with larger grains, and thus suppresses the contributions of polar nanoregions and defect-induced built-in field to ferroelectric property, leading to non-ergodic relaxor state. This work clearly demonstrates the nonnegligible effects of TiO2 reactants on the microstructure and properties of BNST ferroelectric ceramics.

Electrostatic energy storage performances of La(Ni2/3Ta1/3)O3‐modified Na0.5Bi0.5TiO3 lead‐free ceramics

AbstractCeramic capacitors with high electrostatic energy storage performances have captured much research interest in latest years. Sodium bismuth titanate (Na0.5Bi0.5TiO3)‐based ferroelectric ceramics show great potential due to their environment‐friendly composition, high polarization, and excellent relaxor properties. However, the nonergodic relaxor state of Na0.5Bi0.5TiO3‐based ceramics hampers the decrement of remanent polarization, leading to poor energy storage performance. Herein, the (1 − x)Na0.5Bi0.5TiO3–xLa(Ni2/3Ta1/3)O3 ceramics were designed to generate the transformation between nonergodic and ergodic relaxor state. As a result, the ceramics exhibit improved dielectric relaxation, slim polarization–electric field loops, and flattened current–electric field curves due to highly dynamic polar nanoregions. Particularly, the 0.85Na0.5Bi0.5TiO3–0.15La(Ni2/3Ta1/3)O3 ceramics show large breakdown electric field Eb (345 kV/cm), high recoverable energy density Wrec (3.6 J/cm3), and efficiency η (80.6%), revealing potential applications in electrostatic energy storage.