Diffuse Phase Transition Research Articles

Diffuse Ferroelectric Phase Transition-Dependent Photovoltaic Effect in BiFeO3-BaTiO3-Based Solid Solutions.

The photovoltaic effect in ferroelectric (FE) semiconductors, i.e., the FPV effect, is attracting increasing attention. However, the microscopic mechanism of the FPV effect is still largely unknown. Here, we investigated the effects of crystal structure, dielectric, FE, and domain features on the FPV effect in the 0.7BiFe1-xCrxO3-0.3BaTi1-xMnxO3 (BFC-BTM) (0.01 ≤ x ≤ 0.07) system. We observed a coexisting rhombohedral and tetragonal to pseudocubic phase transition for x ≥ 0.05. This structural transition was accompanied by a significant reduction in the lattice distortion and disappearance of macro-sized FE domains. We found a substantial increase and decrease in the degree of the diffuseness of the relaxor FE phase transition and the open-circuit photovoltage VOC, respectively, for x ≥ 0.05, in contrast to the relatively weak variation in the remnant polarization. Our results demonstrate that the FPV effect depends weakly on FE polarization but strongly on the complex submicron domain-related diffused relaxor FE phase transition and crystal structure in BFC-BTM. These results were discussed based on the non-centrosymmetry-related shift current mechanism.

Large Room-Temperature Electrocaloric Effect in Lead-Free Relaxor Ferroelectric Ceramics with Wide Operation Temperature Range.

In order to obtain large room-temperature electrocaloric effect (ECE) and wide operation temperature range simultaneously in lead-free ceramics, we proposed designing a relaxor ferroelectric with a Tm (the temperature at which the maximum dielectric permittivity is achieved) near-room temperature and glass addition. Based on this strategy, we designed and fabricated lead-free 0.76NaNbO3-0.24BaTiO3 (NN-24BT) ceramics with 1wt.% BaO-B2O3-SiO2 glass addition, which showed distinct relaxor ferroelectric characteristics with strongly diffused phase transition and a Tm near-room temperature. Based on a direct measurement method, a large ΔT (adiabatic temperature change) of 1.3 K was obtained at room temperature under a high field of 11.0 kV mm-1. Additionally, large ECE can be maintained (>0.6 K@6.1 kV mm-1) over a broad temperature range from 23 °C to 69 °C. Moreover, the ECE displayed excellent cyclic stability with a variation in ΔT below ±7% within 100 test cycles. The comprehensive ECE performance is significantly better than other lead-free ceramics. Our work provides a general and effective approach to designing lead-free, high-performance ECE ceramics, and the approach possesses the potential to be utilized to improve the ECE performance of other lead-free ferroelectric ceramic systems.

Thermally-induced diffusion and structural phase transitions in Pt/Mn and Pt/Mn/Pt thin films

We demonstrate the possibility of diffusion formation of the chemically ordered L1 0-MnPt phase through the vacuum annealing of Pt(24 nm)/Mn(20 nm) and Pt(12 nm)/Mn(20 nm)/Pt(12 nm) layered stacks at 400 °C for 30 min. For the bi-layered stack annealed at 400 °C, the effect of Pt atoms segregation at the film/substrate interface was detected, which remained after annealing even at higher temperatures (500 °C and 600 °C) and prevented the whole homogenization of the chemical composition through the film depth. By contrast, for the tri-layered stack annealed at 400 °C, the presence of the additional Pt bottom layer enabled to change the rate and mechanism of reactive diffusion, leading to homogeneous distribution of components and enhanced crystallinity of the ordered L1 0-MnPt phase compared to the bi-layered sample. An explanation of the obtained experimental data is provided based on the fundamentals of mass transfer theory and its quantitative parameters (e.g. activation energy and diffusion coefficients).

Investigating structural, dielectric and energy storage properties of NaNbO3 based ferroelectric ceramics

Sodium niobate (NaNbO3) based dielectric materials are getting recognition for the electric energy storage applications due to their promising ferroelectric/anti-ferroelectric properties. In the present work, (0.95-x)NaNbO3-0.05SrTiO3-xBi(Fe1/3Zn1/3Ti1/3)O3 (abbreviated as NNSTBFZT, x=0.04, 0.07 and 0.10) lead-free ferroelectric ceramics were synthesized using conventional solid-state reaction technique. A magnificent recoverable energy storage density (Wrec) and an ultrahigh energy storage efficiency (η) have been observed for x4 (∼1.05 J/cm3) and x10 (∼85 %) samples, respectively which reliant on the non-equivalent replacement of ions at the A and B sites of perovskite unit cell. Further, the phase investigation has been studied using X ray diffraction and Raman spectroscopy, which elucidate the effect of incorporation of the substituent ions at host matrix properly. A moderate dielectric constant with ultralow losses has been obtained and all the samples show diffuse phase transition, which is in favor of enhanced energy storage parameters. Moreover, the morphological analysis indicates decrease in grain size ∼ 1 µm, which also reflects the increased breakdown strength responsible for enhancing energy storage capacity. Therefore, proposed sodium niobate based ceramics become favorable for high energy dielectric capacitors applications.

Enhanced functionalities of isovalently substituted 0.67(Bi1-xLaxFe0.97Ga0.03O3)-0.33(BaTiO3) relaxor piezoceramics synthesized via air quenching

The isovalently substituted lead-free binary solid solution, 0.67(Bi1-xLaxFe0.97Ga0.03O3)-0.33(BaTiO3) (BF-BT) (x ≤ 0.07), has been synthesized by solid state ceramic method via air quenching sintering. FTIR and XRD along with Rietveld structure refinement confirmed a pure perovskite phase with a pseudocubic structure (space group Pm3‾m) for developed compositions. SEM revealed a dense microstructure with fine grain size (<1.5 μm) and minimal porosity. XPS analysis reveals predominantly Bi+3 and Fe+3 states, along with oxygen vacancies (VO··). Ferroelectric studies demonstrated a maximum remanent polarization (Pr) of 12.3 μC/cm2 and coercive field EC of 30.95 kV/cm for La3+ concentration of x = 0.03. Overall decrement in Pr can be attributed to dipolar defect-induced random fields reducing the activation barrier for domain nucleation. Leakage current measurement reveals improved resistivity (∼108 Ω cm) up to an applied field of 30 kV/cm. Dielectric measurements unveiled two frequency-dependent anomalies in temperature dependence above room temperature, indicative of diffuse phase transitions. The Vogel-Fulcher model depicted an increasing freezing temperature (from 465 K for x = 0.01–551 K for x = 0.07) and decreasing activation energy (from ∼0.61 eV to 0.07 eV) with increasing La3+ concentration. The estimated diffuseness parameter around ∼2 suggested relaxor behavior. Doping with La resulted in increased dielectric permittivity at 10 kHz (from 4100 to 24066), showcasing the efficacy of site engineering in augmenting the functional properties of BF-BT for high-temperature dielectric and transducer applications.

Effect of milling time on structural and electrical properties of thermomechanically synthesized of Ba0.1 (Bi0.45Na0.45)TiO3 nanoceramics for ferroelectric random-access memory device

Lead-free Ba0.1(Bi0.45Na0.45)TiO3 (BBNTO) nanoceramics were synthesized using high-energy ball milling, followed by a solid-state reaction method. XRD analysis of the microstructure indicated the formation of tetragonal symmetry. The crystallite size of the nanoceramic powder decreased from ∼ 28 nm to 10 nm after milling for 0, 30, 60, and 90 hours. The dielectric properties of the nanoceramics showed significant improvement, with a diffuse phase transition occurring around 80 °C). The dielectric constant increased with temperature across various frequencies, reached a maximum value at approximately at temperature ∼ 380 °C. At lower temperatures and higher frequencies, the relative permittivity and tangent loss depend on the crystallite size and milling duration. Impedance spectroscopy data analysis revealed size-dependent impedance characteristics and dielectric relaxation. The ac conductivity plot adhered to the Arrhenius relation, and the calculated activation energy confirmed the negative temperature coefficient of resistance (NTCR) behavior. P-E loops confirmed ferroelectric properties, indicating potential for use in future ferroelectric-based storage devices.

Improving the Energy Storage Performance in Bi0.5Na0.5TiO3-Based Ceramics by Combining Relaxor and Antiferroelectric Properties.

Ceramic capacitors have received great attention for use in pulse power systems owing to their ultra-fast charge-discharge rate, good temperature stability, and excellent fatigue resistance. However, the low energy storage density and low breakdown strength (BDS) of ceramic capacitors limit the practical applications of energy storage technologies. In this work, we present a series of relaxor ferroelectric ceramics (1-x) [0.94 Bi0.5Na0.5TiO3 -0.06BaTiO3]- x Sr0.7Bi0.2TiO3 (1-x BNT-BT- x SBT; x = 0, 0.20, 0.225, 0.25, 0.275 and 0.30) with improved energy storage performances by combining relaxor and antiferroelectric properties. XRD, Raman spectra, and SEM characterizations of BNT-BT-SBT ceramics revealed a rhombohedral-tetragonal phase, highly dynamic polar nanoregions, and a reduction in grain size with a homogeneous and dense microstructure, respectively. A high dielectric constant of 1654 at 1 kHz and low remnant polarization of 1.39 µC/cm2 were obtained with the addition of SBT for x = 0.275; these are beneficial for improving energy storage performance. The diffuse phase transition of these ceramics displays relaxor behavior, which is improved with SBT and confirmed by modified the Curie-Weiss law. The combining relaxor and antiferroelectric properties with fine grain size by the incorporation of SBT enables an enhanced maximum polarization of a minimized P-E loop, leading to an improved BDS. As a result, a high recoverable energy density Wrec of 1.02 J/cm3 and a high energy efficiency η of 75.98% at 89 kV/cm were achieved for an optimum composition of 0.725 [0.94BNT-0.06BT]-0.275 SBT. These results demonstrate that BNT-based relaxor ferroelectric ceramics are good candidates for next-generation ceramic capacitors and offer a potential strategy for exploiting novel high-performance ceramic materials.

Modeling phase separation in solids beyond the classical nucleation theory: Application to FeCr.

Despite a large amount of work being devoted to study the phase separation in solids, the underlying physical mechanism responsible for such diffusive first-order phase transitions remains difficult to model outside the spinodal regime, i.e., in the nucleation and growth regime. This work presents an alternative of the classical nucleation theory for modeling phase separation in this regime, even for systems far from the solubility limit, i.e., for high degree of meta-stability where the classical nucleation theory does not hold. This method then allows a direct comparison between simulations and experiments always performed in solids with a high degree of meta-stability.

Efek Pendoping Nd3+ Pada Senyawa BaBi2-xNdxNb2O9 Terhadap Struktur, Sifat Dielektrik Dan Optik

The Aurivillius compound with formula BaBi2-xNdxNb2O9 (x = 0.05, 0.1, 0.2, and 0.4) has been successfully synthesized using the molten salt method, showing potential as a ferroelectric material. The impact of Nd3+ substitution on the structure, morphology, dielectric, and optical properties has been systematically analyzed. XRD data refinement confirms that BaBi2-xNdxNb2O9 (BBNN) exhibits an orthorhombic structure with an A21am space group. Anisotropic plate-like grains were observed across all samples, decreasing their size as Nd3+ content increases. The ferroelectric transition temperature (Tc) decreases due to structural distortion caused by the reduction of the lone pair 6s2 electron effect of Bi3+ when substituted with Nd3+. Moreover, this structural distortion also contributes to an increase in bandgap energy (Eg). The diffuse ferroelectric phase transition is characterized by a broadened Tc peak induced by Nd3+ substitution due to increased cationic disruption in the bismuth layers. The ferroelectric phase with a lower and broader Tc suggests that the x = 0.4 sample has the potential for electrocaloric applications.

High Piezoelectric Performance of KNN-Based Ceramics over a Broad Temperature Range through Crystal Orientation and Multilayer Engineering.

Uninterrupted breakthroughs in the room temperature piezoelectric properties of KNN-based piezoceramics have been witnessed over the past two decades; however, poor temperature stability presents a major challenge for KNN-based piezoelectric ceramics in their effort to replace their lead-based counterparts. Herein, to enhance temperature stability in KNN-based ceramics while preserving the high piezoelectric response, multilayer composite ceramics were fabricated using textured thick films with distinct polymorphic phase transition temperatures. The results demonstrated that the composite ceramics exhibited both outstanding piezoelectric performance (d33~467 ± 16 pC/N; S~0.17% at 40 kV/cm) and excellent temperature stability with d33 and strain variations of 9.1% and 2.9%, respectively, over a broad temperature range of 25-180 °C. This superior piezoelectric temperature stability is attributed to the inter-inhibitive piezoelectric fluctuations between the component layers, the diffused phase transition, and the stable phase structure with a rising temperature, as well as the permanent contribution of crystal orientation to piezoelectric performance over the studied temperature range. This novel strategy, which addresses the piezoelectric and strain temperature sensitivity while maintaining high performance, is well-positioned to advance the commercial application of KNN-based lead-free piezoelectric ceramics.

Integrated structural and functional analysis of Ba1-xSrxTiO3-Bi0.5Na0.5TiO3 ceramics: Insights into energy storage and electrocaloric performance

This paper reports an extensive investigation on the structural, dielectric, ferroelectric and pyroelectric properties of 0.7Ba1-xSrxTiO3 – 0.3Bi0.5Na0.5TiO3 (x = 0.0, 0.5, 0.6, 0.7) ceramics synthesized via conventional solid-state reaction (SSR) technique. X-ray diffraction data confirms the presence of pure perovskite phase. The variation of lattice parameters with strontium concentration in 0.7Ba1-xSrxTiO3 – 0.3Bi0.5Na0.5TiO3 ceramics were evaluated using the Rietveld refinement of the XRD data. The variation of dielectric permittivity with temperature (ε' ∼ T) shows the diffused phase transition and all the parameters related to the relaxor ferroelectrics (relaxation coefficient, activation energy and freezing temperature) were evaluated. The energy storage properties of the as-prepared ceramics were evaluated using the room temperature PE loop. Amongst the as-prepared ceramics, the composition with x = 0.5 possesses the highest energy storage density of 0.46 J/cm3 with an efficiency of 90 %. The temperature dependent P-E loops were used to study the electrocaloric effect (ECE). The ECE calculations were performed using in-direct method based on Maxwell's thermodynamic relations. A maximum adiabatic temperature change of 0.32 K is achieved at 268 K under a small applied electric field of 25 kV/cm for the ceramic with Sr content x = 0.5. Additionally, electrocaloric responsivity ξmax = 0.13 K mm/kV was also found for the studied ceramics. The above results show that the ceramic 0.7Ba1-xSrxTiO3 – 0.3Bi0.5Na0.5TiO3 with the composition x = 0.5 is a viable lead-free option for application in solid state refrigeration.

Investigate the effect of co-doping on the grain size and diffuse phase transition of barium titanate ceramics

An investigation examined the impact of co-doping BaTiO3 ceramics with La3+ and Nd3+ on their microstructural, dielectric, and phase transition properties. The synthesis of BaTiO3 with co-doping of La3+ and Nd3+, using the general formula Ba1-x(La1/3, Nd1/3)xTiO3 (BLNdTx) with varying concentrations of x (0%, 2%, 4%, and 8%), is achieved by the solid-state reaction technique. A temperature-dependent dielectric permittivity investigation was conducted at four distinct frequencies (1 kHz, 10 kHz, 100 kHz, 500 kHz, and 1 MHz) within the 30–200 °C temperature range. The findings indicate that the samples show a diffuse phase transition and a noticeable divergence from the typical Curie-Weiss equation. The diffuseness parameters γ for phase transition rose from 1.15 to 1.75 as x grew from 0 to 8%, respectively. The concurrent impact of surface phenomena, mechanical stress phenomena, and the external effect of grain boundaries might explain the substantial size reduction. An in-depth understanding of the grain size effect and its underlying mechanism would be advantageous for advancing and practically using BaTiO3-based ceramics and other ferroelectrics.

Thermal and electromechanical performance in BaSnO3-modified potassium sodium niobate piezoceramics via two-step sintering

In view of industrial applications requiring high piezoelectric activity, KNN-based ceramics face two key constraints: insufficient density and temperature sensitivity. To address these challenges, this study first introduces BaSnO3 and employs two-step sintering method (TSS) for fabrication, thereby synthesizing ternary 0.975K0.5Na0.5NbO3-0.025Bi0.5K0.5TiO3-xBaSnO3 (KNN-1000xBaSn; x = 0, 0.3 %, 0.6 % and 0.9 %) with superior piezoelectricity (d33 = 217–257 pC/N; d33* = 265–330 pm/V; S = 0.16–0.21 %), high Curie temperature (TC = 325–349 °C) and densification (4.3–4.5 g/cm3; relatively density ∼96 %). In one respect, the TSS allows minimal volatilization of alkali metals while promoting grain homogenization. In another respect, the introduction of BaSnO3 enhances the mobility of domain walls, meanwhile fosters diffuse phase transitions (DPT) and widens dielectric peaks without significantly impairing TC. Moreover, the KNN–6BaSn obtain not only reinforced d33 (256 pC/N) with high TC (325 °C) and ε′ (1016), but also fatigue resistance and extreme-temperature endurance with excellent d33* (445 pm/V at 90 °C; 300 pm/V at 180 °C). This work provides a resultful dual-strategy for the emergence of lead-free piezoelectric products.

Unveiling a giant electrocaloric effect at low electric fields through continuous phase transition design

The reported electrocaloric (EC) effect in ferroelectrics is poised for application in the next generation of solid-state refrigeration technology, exhibiting substantial developmental potential. This study introduces a novel and efficient EC effect strategy in (1–x)Pb(Lu1/2Nb1/2)O3-xPbTiO3 (PLN-xPT) ceramics for low electric-field-driven devices. Phase-field simulations provide fundamental insights into thermally induced continuous phase transitions, guiding subsequent experimental investigations. A comprehensive composition/temperature-driven phase evolution diagram is constructed, elucidating the sequential transformation from ferroelectric (FE) to antiferroelectric (AFE) and finally to paraelectric (PE) phases for x=0.10−0.18 components. Direct measurements of EC performance highlight x=0.16 as an outstanding performer, exhibiting remarkable properties, including an adiabatic temperature change (ΔT) of 3.03 ​K, EC strength (ΔT/ΔE) of 0.08 ​K ​cm kV−1, and a temperature span (Tspan) of 31 ​°C. The superior EC effect performance is attributed to the temperature-induced FE to AFE transition at low electric fields and diffusion phase transition behavior contributing to the wide Tspan. This work provides valuable insights into developing high-performance EC effect across broad temperature ranges through the strategic design of continuous phase transitions, offering a simplified and economical approach for advancing ecofriendly and efficient solid-state cooling technologies.

The Influence of Lanthanum Admixture on Microstructure and Electrophysical Properties of Lead-Free Barium Iron Niobate Ceramics.

This article presents the research results of lead-free Ba1-3/2xLax(Fe0.5Nb0.5)O3 (BFNxLa) ceramic materials doped with La (x = 0.00-0.06) obtained via the solid-state reaction method. The tests of the BFNxLa ceramic samples included structural (X-ray), morphological (SEM, EDS, EPMA), DC electrical conductivity, and dielectric measurements. For all BFNxLa ceramic samples, the X-ray tests revealed a perovskite-type cubic structure with the space group Pm3¯m. In the case of the samples with the highest amount of lanthanum, i.e., for x = 0.04 (BFN4La) and x = 0.06 (BFN6La), the X-ray analysis also showed a small amount of pyrochlore LaNbO4 secondary phase. In the microstructure of BFNxLa ceramic samples, the average grain size decreases with increasing La content, affecting their dielectric properties. The BFN ceramics show relaxation properties, diffusion phase transition, and very high permittivity at room temperature (56,750 for 1 kHz). The admixture of lanthanum diminishes the permittivity values but effectively reduces the dielectric loss and electrical conductivity of the BFNxLa ceramic samples. All BFNxLa samples show a Debye-like relaxation behavior at lower frequencies; the frequency dispersion of the dielectric constant becomes weaker with increasing admixtures of lanthanum. Research has shown that using an appropriate amount of lanthanum introduced to BFN can obtain high permittivity values while decreasing dielectric loss and electrical conductivity, which predisposes them to energy storage applications.

Improvement of energy storage properties of NN-based ceramics by high-entropy strategy and A-site cation vacancies

High-entropy dielectric capacitors have recently drawn increasing attention in the field of energy storage. In this study, NiO has been incorporated into [(Na0.7Bi0.1)0.8Sm0.02Ca0.02Sr0.02Ba0.02]Nb0.8Sb0.1Ta0.1O3-based ceramics. We applied the concept of high-entropy design to introduce cation vacancies at the A-site, enhancing conformational entropy. This approach led to the successful preparation of a novel type of energy-storage ceramics with an ABO3 perovskite structure, denoted as (1-x)NBSCSBNST-xNiO (x = 0, 0.02, 0.04, & 0.06). We conducted a systematic study of the microstructural, dielectric, and ferroelectric characteristics, along with an exploration of the influence of the high-entropy strategy on their performance. The ΔSconfig increases with NiO doping, and the Eb of the NBSCSBNST-0.02Ni sample exhibits a significant increase to 730 kV/cm from 550 kV/cm of NBSCSBNSTN. This enhancement is accompanied by a recoverable energy density (Wrec) of 4.43 J/cm3 and an efficiency (η) of 75.9 %. As the content of NiO increases from x = 0 to x = 0.06, the phase transition diffusion behavior strengthens. Additionally, the permittivity (εr) spectrum becomes more uniform, and the activation energy of the prepared ceramic samples increases from 1.03 eV to 1.76 eV. This effect suppresses the emergence of localized electric branching, eventually improving the breakdown strength of NBSCSBNST-xNi ceramic materials. The obtained results indicate that the concept of high-entropy design to introduce cation vacancies at the A-site is an efficient approach to improve the energy storage characteristics of lead-free dielectric capacitors.

Structural analysis, relaxor-ferroelectric behavior and optical properties of Mn3+-doped CaBi3NdTi4O15 synthesized via hydrothermal technique

In this study, the synthesis of the Aurivillius Ca1-xBi3+xNdTi4-xMnxO15 (CBNTMx), where x is 0, 0.2, and 0.4, was carried out using the hydrothermal technique. The X-ray diffraction (XRD) data showed that the polar orthorhombic structure in space group of A21am was adopted by all powder samples. All samples possessed anisotropic plate-like particle shapes, and the particle size increased with increase in x value. The phase transition temperature (Tm) is decreased by the ionic substitution owing to the decrease in orthorhombic distortion reflected by the reduction of orthorhombicity. Relaxor-ferroelectric behavior was observed for CBNTM0.4 because of its strong frequency dispersion, while CBNTM0 and CBNTM0.2 only showed a diffused-phase transition (DPT) indicated by the broad dielectric constant at the transition temperature (Tm). The electrical conductivity exhibited an enhancement at higher x value since the ionic substitution with acceptor Mn3+ ions introduced the charge carrier in the lattice. Similarly, the reduction of optical band gap energy from 3.43 eV for the parent CBNTM0 to 2.75 eV and 2.71 eV for CBNTM0.2 and CBNTM0.4, respectively, was described as the contribution of the lower energy level of Mn 3d orbital than that of Ti 3d in the conduction band and also the less distorted structure.

Doping effects and role conversion of CeO2 in 0.3PZN–0.7PZT ternary piezoelectric ceramics with enhanced electrical properties

In this work, the rare-earth doped ternary lead zirconate titanate ceramics with chemical formula of [0.3Pb(Zn1/3Nb2/3)O3–0.7Pb(Zr0.52Ti0.48)O3] + x wt% CeO2 (x=0–0.5, abbreviated as 0.3PZN–0.7PZT–xCe) were synthesized by a conventional solid-state reaction route, specific attentions was focused on the effects of CeO2 dopants on the structures and electrical properties of the 0.3PZN–0.7PZT ceramics, revealing the role conversion of CeO2 dopants with its doping amount (x). When less CeO2 (x≤0.2) is introduced into 0.3PZN–0.7PZT, the prepared ceramics are identified as the coexistence of rhombohedral and tetragonal phases, also involved with an increased grain size and a reduced atomic ratio of Pb/(Zr+Ti+Zn+Nb). The increased remanent polarization (Pr) and deceased coercive filed (Ec), as well as improved dielectric permittivity (εr) and piezoelectric coefficient (d33) demonstrate the donor substitution of Ce3+ for Pb2+ at the A-site of perovskite lattice. Conversely, the introduction of excessive CeO2 (x>0.2) causes a reversal evolution in the electrical properties of ceramics, suggesting that some of the introduced cerium element tends to become Ce4+, which equivalently substitutes for Zr4+ at the B-site. Additionally, the diffused phase transition (DPT) behaviors of the 0.3PZN–0.7PZT–xCe ceramics were investigated by the modified Curie–Weiss Law. The sample with x=0.2 shows reduced DPT character and optimized electrical properties, including TC=297 °C, εr=1400, d33=480 pC/N, tanδ=1.6%, kp=65%, d33×g33=16.32×10–12 m2/N, Pr=38.3 μC/cm2 and Ec=1.02 kV/mm. These enhanced electrical properties not only are contributed by the donor substitution effect of Ce3+, but also benefit from the optimized morphotropic phase boundary that is close to the tetragonal-rich side.

Properties of tape cast (Na, K, Li) (Nb, Sb, Ta)O3 -based ceramics sintered in reduced atmosphere and its application in triaxial piezoelectric accelerometer

In this study, we utilized the tape-casting method to produce Pb-free (Na0·52K0·4425Li0.0375) (Nb0·8925Sb0·07Ta0.0375)O3 + 2 mol% MnCO3 + y mol% LiF (y = 0 to 3) piezoelectric ceramics. We investigated the impact of LiF sintering in a reduced atmosphere on microstructure, dielectric properties, impedance spectroscopy, and piezoelectric performance. By analyzing the degree of diffuse phase transition, we observed increased density and enhanced long-range order in the sample doped with 1 mol% LiF, which exhibited optimal piezoelectric properties (d33 = 265 pC/N and kp = 0.437) and a minimal diffusion parameter. Moreover, LiF doping enabled sintering at 1020 °C under low PO2, facilitating potential co-firing with Cu inner electrodes to further enhance the piezoelectric performance. Using the optimized parameters, we fabricated a cross-type triaxial piezoelectric accelerometer, demonstrating sensitivities of 2.33, 2.44, and 10.6 mV/g along the X, Y, and Z axes, respectively, with a resonance frequency of ∼2600 Hz and frequency range of ∼1300 Hz. This accelerometer holds promise for vibration measurements in low-frequency mechanical systems.

Enhanced energy storage performance, breakdown strength, and thermal stability in compositionally designed relaxor Eu3+ substituted Na0.2K0.3Bi0.5TiO3

Lead-free Eu3+ substituted NKBT ceramics (Na0.2K0.3Bi0.5-xEuxTiO3, x = 0 (Eu 0),0.02(Eu 2),0.04(Eu 4), and 0.06(Eu 6)) were strategically designed via a local random field approach. The structural evolution had been confirmed through X-ray diffraction analysis. The observation of a broad dielectric curve supported the enhanced relaxor nature and the phenomena reflected in the P-E and S-E loops. The diffuse phase transition transforms to the plateau-type feature with excellent thermal stability with ±20 % and ± 40 % variation in dielectric constant over the temperature range of 120 to 500 °C and 90 to 500 °C, respectively in Eu 4. A large recoverable energy density of 1.7 J/cm3 with a high breakdown strength of 188 kV/cm was achieved in the Eu 2 sample at room temperature, making it a potential candidate for energy storage application. Moreover, the frequency stability (0.1 to 500 Hz range), thermal stability (45 °C to 85 °C), and fatigue measurement (10−1 to 106 cycles) were performed from the application point of view. The highest efficiency (82 %) was also achieved in the Eu 6. The negligible Sneg of Eu-rich compositions proves the existence of a relaxor state when the field is removed, and it transforms into the ergodic relaxor state. Furthermore, the SRBRF model is exploited to understand and correlate the transformation from normal to relaxor ferroelectrics with their properties. The current study provides a novel idea for compositional design for energy density, efficiency, and thermal stability ceramics by modifying and creating weakly coupled polar phases with rare earth substitution.