TiO3 Content Research Articles

Zero-Temperature Coefficient of Resonant Frequency in [(Mg0.6Zn0.4)0.95Co0.05]1.02TiO3.02-Ca0.6(La0.9Y0.1)0.2667TiO3 Ultra-Low-Loss Composite Dielectrics

Investigating the microwave dielectric properties of ceramics prepared through the conventional solid-state route, such as x[(Mg0.6Zn0.4)0.95Co0.05]1.02TiO3.02-(1−x)Ca0.6(La0.9Y0.1)0.2667TiO3, reveals notable characteristics. [(Mg0.6Zn0.4)0.95Co0.05]1.02TiO3.02 shows a permittivity (εr) of approximately 20, a high quality factor (Q × f) ranging between 250,000 and 560,000 GHz, and a temperature coefficient of resonant frequency (τf) of approximately −65 ppm/°C. To enhance the temperature stability, Ca0.6(La0.9Y0.1)0.2667TiO3 featuring a τf value of +374 ppm/°C was incorporated into the [(Mg0.6Zn0.4)0.95Co0.05]1.02TiO3.02 composition. τf demonstrated an increase with rising Ca0.6(La0.9Y0.1)0.2667TiO3 content, reaching zero at x = 0.95. A ceramic composition of 0.95[(Mg0.6Zn0.4)0.95Co0.05]1.02TiO3.02-0.05Ca0.6(La0.9Y0.1)0.2667TiO3, incorporating 3wt.% BaCu(B2O5) as sintering aids, exhibited outstanding microwave dielectric properties: εr~22.5, Q × f~195,000 (at 9 GHz), and τf~0.1ppm/°C, with a sintering temperature at 950 °C. This material is proposed as a prospective candidate for 6G band components and GPS antennas.

Enhancing Fast-Charge Capabilities in Solid-State Lithium Batteries through the Integration of High Li0.5La0.5TiO3 (LLTO) Content in the Lithium-Metal Anode.

Solid-state batteries (SSBs), which have high energy density and are safe, are recognized as an important field of study. However, the poor interfacial contact with high resistance, the dendrite problem, and the volume change of the metallic lithium anode prevent the use of SSBs. Li0.5La0.5TiO3 (LLTO) particles and molten lithium were used to create a high-performance LLTO-Li composite lithium with a sequential ion-conducting phase. With garnet electrolytes, this lithium has better wettability and reduced surface tension. To compensate for the lithium depletion that occurs during stripping, the Li-Ti phase with a high ionic diffusion coefficient that forms in the anode can rapidly transport lithium from the bulk to the solid-state interface, ensuring tight interface contact, preventing the formation of gaps, and homogenizing the current and Li+ flux. The LLTO-Li| LLZTO| LLTO-Li symmetric cell exhibits a good cyclic stability of 1000 h at room temperature, a low interfacial resistance of 22 Ω cm2, and a high critical current density of 1.2 mA cm-2. Furthermore, fully built cells with a LiFePO4 cathode showed outstanding cycling performance, maintaining 95% of their capacity after 900 cycles at 1 C and 92% capacity retention after 100 cycles at 2 C.

Antiferroelectric orthorhombic P-to-R phase transition induced exotic electrocaloric effect in NaNbO3-based lead-free ceramics

Phase transition is expected in designing high-performance electrocaloric effect (ECE). However, hidden antiferroelectricity in NaNbO3-based ceramics complicates ECE evolution as compared to conventional ferroic materials. Therefore, a NaNbO3−xBi0.5Li0.5TiO3 (x = 0.08, 0.10, and 0.12) system is introduced to explore ECE performance in P (Pbma), Q (P21ma), and R (Pnma) phases since a Bi0.5Li0.5TiO3 dopant plays a Janus role in stabilizing ferroelectric Q (x = 0.08 and 0.10) and inducing the antiferroelectric (AFE) relaxor R phase (x = 0.12). Rietveld refinement reveals a phase structure change from the P/Q to R state. Bi0.5Li0.5TiO3 addition makes a downshift of P-to-R transition temperature accompanied by an increase in relaxation property, as certified by dielectric analysis/piezoelectric force images, in situ XRD/Raman spectra, and ferroelectric tests. Additionally, a square P–E loop evolves into less-sharp and finally changes into a slant one with increasing Bi0.5Li0.5TiO3 content. ECE is directly measured, and its peak value increases from 0.15 K for x = 0.08 and 0.21 K for x = 0.10 and finally to 0.11 K for x = 0.12 composition. Interestingly, dual ECE peaks appear in x = 0.10, and it is probably contributed by R relaxor polar nanodomains. This work not only clarifies actual ECE behavior in AFE orthorhombic (P/R) NaNbO3-based ceramics but also fulfills understandings of AFE P-to-R transitions in modulating ECE.

Microwave Dielectric Properties and Sintering Behavior of K20 Series Temperature‐Stable 0.91MgTiO3‐0.09(Ca0.8Na0.1Ce0.1)TiO3 Composite Ceramics

AbstractRecently, the progress of miniaturization and integration for dielectric communication devices is being motivated by the rapidly‐developed communication technology. Microwave dielectric ceramics, the foundation of dielectric communication devices, have been receiving great attention. In this study, 0.91MgTiO3‐0.09(Ca0.8Na0.1Ce0.1)TiO3 ceramic (0.91MT‐0.09CNCT) was synthesized by the traditional solid‐phase process to tune the temperature coefficient of resonant frequency (τf) to zero. Compared with 0.95MgTiO3–0.05CaTiO3 ceramic, a Q×f value increased by 15 % was achieved in 0.91MT‐0.09CNCT ceramic, meanwhile, the sintering temperature of which was significantly lowered by 225 °C. In general, the τf value is related to the (Ca0.8Na0.1Ce0.1)TiO3 content and sintering temperature. At the same time, the 0.91MT‐0.09CNCT ceramic sintered at 1175 °C has competitive dielectric properties: ϵr=20.4, Q×f=66,000 GHz, τf=0.2 ppm/°C, which suggests it a promising candidate for dielectric communication devices with low cost and green synthesis.

Novel temperature stable Li2Mg3ZrO6 microwave dielectric ceramics with Ca0.8Sr0.2TiO3 addition

Novel temperature stable Li2Mg3ZrO6 microwave dielectric ceramics were fabricated by a conventional solid-state route. With increasing Ca0.8Sr0.2TiO3 content x, CaZrO3 phase was formed and a near-zero τf value was obtained at 1350 °C for x = 0.21. Li2Mg3ZrO6-based ceramics displayed well microwave dielectric properties of εr = 16.2, Q × f = 46370 GHz, τf = 4.5 ppm/°C when Ca0.8Sr0.2TiO3 content x is 0.21.

Changing the polar order using different sintering methods

In this study, solid solution ceramics (1–x)Bi0.5K0.5TiO3–xBi0.2Sr0.7TiO3 (x = 0.1, 0.15 and 0.2, abbreviated as BKST1 for a one-step sintering method and as BKST2 for a two-step sintering method) were prepared using two different sintering methods. The BKST1 ceramics exhibited an average cubic structure, while the BKST2 ceramics had tetragonal distortions. As the Bi0.2Sr0.7TiO3 content increased, spontaneous relaxor-ferroelectric transition disappeared in the BKST1 ceramics owing to the formation of the polar nanoregions (PNRs). The compositions developed using the two-step sintering method exhibited a noticeable dielectric anomaly with respect to spontaneous relaxor-ferroelectric transitions. Double ferroelectric hysteresis loops appeared near the ergodic relaxor-ferroelectric (or non-ergodic relaxor) transition points. The relationship between the piezoelectric coefficient (d33) and compositions suggested that 0.15BKST1 exhibited the optimum piezoelectric properties (d33, 128 pC/N). The 0.15BKST ceramic developed using the one-step sintering method had a low depolarisation temperature (~176 °C in 0.15BKST1 compared to ~227 °C in 0.15BKST2). The improved piezoelectric properties were attributed to the electrical field-induced transformation from PNRs to the long-range ferroelectric ordering as evidenced by the poling effects on the XRD patterns and dielectric behaviours.

Fabrication of (Bi0.5K0.5)TiO3 modified BaTiO3-Bi(Mg0.5Ti0.5)O3-BiFeO3 piezoelectric ceramics

The lead-free x(Bi0.5K0.5)TiO3-0.23BaTiO3-0.02Bi(Mg0.5Ti0.5)O3-(0.75-x)BiFeO3 piezoelectric ceramics (x = 0.05, 0.07, 0.09, and 0.11) were prepared by solid-state reaction method. The increase of (Bi0.5K0.5)TiO3 concentration revealed a decrease of dielectric maximum temperature (Tm), however, the values were higher than 420 °C. The Rietveld structure refinement for each composition showed pseudo-cubic symmetry and the rhombohedral distortion (90 - αF) was gradually decreased from 0.27° to 0.09° for x = 0.05 and 0.11, respectively. The saturation and remanent polarization were increased and a coercive field was decreased, while the critical exponent (γ) was increased from 1.407 (x = 0.07) to 1.821 (x = 0.11) revealing more relaxor-like behavior with higher (Bi0.5K0.5)TiO3 content. The remanent polarization, coercive field, and piezoelectric strain constant of 31.9 μC/cm2, 23.6 kV/cm, and 315 pm/V, respectively, obtained in the composition with x = 0.11 are significantly higher than those reported previously for other Bi-based piezoelectric ceramics with Tm>250 °C.

Electrical properties of semi-conductive composites with different Li0.5La0.5TiO3 content

In this study, semi-conductive composites with different contents of the perovskite type ionic conductor Li0.5La0.5TiO3 (LLTO) were synthesized to weaken the positive temperature coefficient (PTC) effect of the semi-conductive composites and inhibit the injection of space charge into the insulation layer. The electrical performance of the composites were evaluated. The results show that the composite with 4 wt% of LLTO effectively weakened the PTC effect and significantly inhibited the space charge injection. The effects of different doping amounts of LLTO on the space charge inhibition and PTC effect reduction of the semi-conducting shielding layer and their interaction mechanisms were studied in detail. The weakening of the PTC effect caused by LLTO may be related to the reconstruction of the carbon black conductive network, while the inhibition of the space charge injection may be due to the Coulomb force exerted by LLTO on the electrons.

Novel thermal‐sensitive properties of NBT‐BZT composite ceramics for high‐temperature NTC thermistors

AbstractWe found for the first time that (1 − x) Na0.5Bi0.5TiO3‐xBiZn0.5Ti0.5O3 (NBT–BZT) composite ceramics showed negative temperature coefficient (NTC) at a high temperature. The NBT–BZT nanopowders were successfully prepared by Pechini method. Their ceramics were sintered at 1100°C. The NBT–BZT ceramic exhibited a good linear relationship between logarithm of electrical resistivity (Inρ) and reciprocal of absolute temperature (1000/T) at 250°C–1050°C. The obtained ρ600, ρ900, and B600/900 constants of the NBT–ZBT NTC thermistors are approximately 5.92 × 106 to 3.01 × 104 Ω cm, 7.03 × 103 to 7.60 × 102 Ω cm and 2.3 × 104‐1.3 × 104 K, respectively. The electrical characteristics can be tuned to the desired value by changing the Na0.5Bi0.5TiO3 content in the compound. The electrical conductivity in these compounds is due to the electron jumps between Ti3+ and Ti4+ and oxygen‐ion conductivity. Results demonstrate a tremendous potential of the studied system for perovskite materials with NTC performance.

Electrical microstructures of CaTiO3-Bi0.5Na0.5TiO3 microwave ceramics with high permittivity (εrmax ∼487)

The (1-x)CaTiO3-xBi0.5Na0.5TiO3 [(1-x)CT-xBNT), x = 0.1–0.6] microwave ceramics were studied by traditional solid-state method. Crystal structures, microstructures, microwave dielectric properties and impedance analysis of the as-prepared ceramics were investigated systematically. Refinement of X-ray diffraction patterns from all of the samples were pure orthorhombic structure with Pbnm space group. The Raman spectra of (1-x)CT-xBNT were in accord with the previous reports except that some abnormal modes appeared in high-wavenumber of 1200 cm−1-3400 cm−1. The microstructures were dominated by even grains and the average sizes increased gradually with an increase in Bi0.5Na0.5TiO3 (BNT) content. The microwave dielectric constant, εr, improved from 184 to 487, and the quality factor, Q×f, decreased constantly from 6973 GHz to 157 GHz as the amount of BNT in (1-x)CT-xBNT increased. However, the temperature coefficient of resonant frequency, τf, was restricted to fluctuating from 680 ppm/°C to 820 ppm/°C due to that the oxygen octahedral was twisted. For analysis and modeling of impedance data of 0.7CT-0.3BNT ceramics, the most appropriate equivalent circuits were found to consist of a parallel resistor-capacitor-constant phase element (R-CPE-C). And the activation energy for grains, 1.8 eV, was different to that in the grain boundaries, 1.0 eV.

Change the ferroelectric properties of Al0.01Ba0.99TiO3 ceramics by Al0.01Sr0.99TiO3 doping

The effect of doping Al0.01Sr0.99TiO3 on the structural, ferroelectric and storage energy properties of Al0.01Ba0.99TiO3, (1 − x) Al0.01Ba0.99TiO3-(x)Al0.01Sr0.99TiO3 (x = 0, 0.005, 0.010, and 0.015) was investigated. The X-ray powder diffraction (XRD) patterns revealed that the studied samples adopt single phase of tetragonal with space group symmetry P4mm. Field emission scanning electron microscopy (FE-SEM) showed that the particle size of pure Al0.01Ba0.99TiO3 (ABTO) was affected by the Al0.01Sr0.99TiO3 (ASTO) content. The dielectric study showed that doping ABTO by ASTO decreased the dielectric permittivity, ac conductivity and Curie-Weiss temperature (TC) of the parent sample. Remnant polarization, saturation, and coercive field were given. Our results show that the ferroelectric behavior of ABTO ceramics is more sensitive to ASTO dopants. Through the ferroelectric hysteresis loops, the energy storage density and the energy-storage efficiency, η of all samples were calculated. The results showed that η for the sample of x = 0.005 is better than that of ABTO.

Structural, electrical, and optical properties of polycrystalline (1−x)BiFeO3-xBi0.5K0.5TiO3 thin films

The effects of multiferroic (1 − x)BiFeO3-xBi0.5K0.5TiO3 (BFO-xBKT, x = 0, 0.1, 0.2, 0.3, and 0.4) thin films on the structural, electrical, and optical properties had been investigated. The phases of all the films corresponded to a perovskite structure according to the X-ray diffraction patterns and the Raman shift measurements. Meanwhile, the merging of (104) and (110) peaks of the BFO-xBKT thin films revealed the phase transition from a rhombohedral structure to a tetragonal structure. The atomic force microscope showed that the BFO-xBKT thin films had uniform morphology and the grain size of the BFO-xBKT thin films became smaller when the Bi0.5K0.5TiO3 content increased. The maximum remnant polarization 2Pr = 17.1 μC/cm2 and lowest leakage current of 3.07×10−7 A/cm2 were observed in the BFO−0.3BKT thin film. The leakage current conduction mechanism displayed Ohmic conduction in the low electric field region and in the high electric field region, the mechanism was dominated by the Fowler−Nordheim tunneling for BFO-xBKT (x = 0.1, 0.2, 0.3, and 0.4) thin films. The absorption edges of BFO-xBKT were blue-shifted with the increasing of the x value.

Ultrahigh energy density and improved discharged efficiency in bismuth sodium titanate based relaxor ferroelectrics with A-site vacancy

Novel A-site deficient (1-x-y)Bi0.5Na0.5TiO3-xBaTiO3-yBi0.2Sr0.7TiO3 lead-free relaxor ferroelectrics have been explored for energy storage property. Particularly slim polarization hysteresis (P-E) loops are observed in 0.655Bi0.5Na0.5TiO3-0.065BaTiO3-0.28Bi0.2Sr0.7□0.1TiO3 (6.5BNBT-BST) at ambient temperature resulting in a giant recoverable energy density (Wrec = 1.5 J cm−3) and extremely high efficiency (η = 90%) at 100 kV cm−1, which are closed related to the track of P-E loops. As the addition of Bi0.2Sr0.7TiO3 (BST) content, the ergodic relaxor phase becomes dominant with dynamic polar nano-regions attributed to the absence of ferroelectric domain in the relaxor phase. Furthermore, the recoverable energy density exhibits small variation in elevated temperature where the depressed polarization is compensated by almost hysteresis free loops (η up to 97%). The achievement of these characteristics in P-E loops provides that Bi0.2Sr0.7TiO3 tailoring by A-site vacancies is a potential route when designing new relaxor ferroelectrics for energy-storage applications.

Mg(Ti0.95Sn0.05)O3–(Ca0.8Sr0.2)TiO3 ceramics: Phase, microstructure, and microwave dielectric properties

The phase, microstructure, and microwave dielectric properties of (1 − x)Mg(Ti0.95Sn0.05)O3–x(Ca0.8Sr0.2)TiO3 (0.01 ≤ x ≤ 0.07) ceramics were investigated. (Ca0.8Sr0.2)TiO3 was used as a τf compensator and was added to Mg(Ti0.95Sn0.05)O3 to obtain a temperature-stable material. The powder X-ray diffraction patterns suggest the presence of Mg(Ti0.95Sn0.05)O3 as the main crystalline phase and Ca0.8Sr0.2TiO3 and MgTi2O5 as the minor phases. With increasing (Ca0.8Sr0.2)TiO3 content, the dielectric constant εr and the temperature coefficient of the resonant frequency τf of the ceramics increases, whereas the unloaded quality factor Qufo decreases. For 0.95[Mg(Ti0.95Sn0.05)O3]–0.05(Ca0.8Sr0.2)TiO3 ceramics sintered at 1375 °C, the dielectric constant εr (21.1), the quality factor Qufo (117,000) at 9 GHz, and the temperature coefficient of the resonant frequency τf (−1.79 ppm/°C) were obtained.

Sintering behavior, crystal structure and microwave dielectric properties of (1−x)Nd[(Zn0.7Co0.3)0.5Ti0.5]O3– x(Na0.5Nd0.5)TiO3 ceramics

(1−x)Nd[(Zn0.7Co0.3)0.5Ti0.5]O3–x(Na0.5Nd0.5)TiO3 (x = 0, 0.2, 0.4, 0.6, 0.8) ceramics were prepared using the solid–state reaction route. The effects of (Na0.5Nd0.5)TiO3 content on the sintering behavior, structural characteristics and microwave dielectric properties of Nd[(Zn0.7Co0.3)0.5Ti0.5]O3 were investigated in detail. (1−x)Nd[(Zn0.7Co0.3)0.5Ti0.5]O3–x(Na0.5Nd0.5)TiO3 ceramics exhibited different sintering characteristics in the whole investigated compositional range. X–ray diffraction analysis showed that a complete solid solution with perovskite structure formed in the composition range of x = 0.2–0.8. Moreover, a structural change from the monoclinic to the cubic perovskite structure occurred at x = 0.8. Compared with the pure Nd[(Zn0.7Co0.3)0.5Ti0.5]O3 ceramics, (1−x)Nd[(Zn0.7Co0.3)0.5Ti0.5]O3–x (Na0.5Nd0.5)TiO3 ceramics displayed more anomalous microstructural characteristics. Microwave measurements indicated that the dielectric constant (εr) increased from 31.15 to 78.4, the quality factor (Q × f) value decreased from 2151300 GHz to 12013 GHz, and the temperature coefficient of resonant frequency (τf) moved to positive from −35.7 ppm/°C to +59.1 ppm/°C with the x value increasing from 0 to 0.8. Typically, 0.6Nd[(Zn0.7Co0.3)0.5Ti0.5]O3–0.4(Na0.5Nd0.5)TiO3 ceramics sintered at 1410 °C for 4 h possessed excellent microwave dielectric properties of εr = 50.21, Q × f = 54714 GHz, τf = −3 ppm/°C.

The temperature stability of dielectric properties in xNa0.5Bi0.5TiO3-(1-x)Ba0.7Sr0.3Ti0.995Zr0.005O3 ceramics

ABSTRACTDielectric composites that comprise Na0.5Bi0.5TiO3 and Ba0.7Sr0.3Ti0.995Zr0.005O3 are synthesized using the wet solid-state method. The effect of Na0.5Bi0.5TiO3/Ba0.7Sr0.3Ti0.995Zr0.005O3 (2:8, 2.5:7.5, 3:7, 3.5:6.5) ratio on phase structure, temperature stability and dielectric properties has been investigated in detail. The XRD results show that the composites are composed of tetragonal perovskite. The composite ceramics with x = 0.3 Na0.5Bi0.5TiO3 content possess a considerable temperature stability. The temperature coefficient of capacitance of this varies from −18.9% to 13.9% in the temperature range between −55°C and 200°C. The results show that xNa0.5Bi0.5TiO3-(1-x) Ba0.7Sr0.3Ti0.995Zr0.005O3 ceramics with temperature stability are a good candidate of lead-free dielectric materials.

A novel temperature-stable and low-loss microwave dielectric using Ca0.8Sr0.2TiO3- modified Li2Mg3TiO6 ceramics

Microstructure and microwave dielectric properties of (1-x)Li2Mg3TiO6-xCa0.8Sr0.2TiO3 (x = 0.03, 0.06, 0.08, 0.09, 0.12) ceramics prepared by the conventional solid state route have been investigated. XRD and SEM-EDS analysis confirmed that ceramics contain Li2Mg3TiO6 and Ca0.8Sr0.2TiO3 phases. The microwave properties exhibited a significant dependence on the sintering temperature and Ca0.8Sr0.2TiO3 content. With increasing addition of Ca0.8Sr0.2TiO3, the dielectric constant $$({\varepsilon _r})$$ increased from 14.3 to 17.4 when samples sintered at 1410 °C for 4 h; the quality factor (Q × f) decreased from 133,905 to 101,000 GHz, and the temperature coefficient of resonant frequency ( $${\tau _f}$$ ) significantly increased from −39 to 6.35 ppm/°C when samples sintered at 1370 °C for 4 h. Sample with 0.91Li2Mg3TiO6-0.09Ca0.8Sr0.2TiO3 sintered at 1370 °C for 4 h possess excellent microwave properties with $${\varepsilon _r}$$ of 16.4, a Q × f of 113,000 GHz and $${\tau _f}$$ of −3.65 ppm/°C. It is proposed as low-loss and low-cost dielectric materials for microwave and millimeter wave application.

Preparation, microstructure and relaxor ferroelectric characteristics of BLNT–BCT lead-free piezoceramics

In the present study, lead-free piezoelectric (1-x)[(Bi0.96La0.04)0.5Na0.5TiO3]-(x)[Ba0.90Ca0.10TiO3] ceramics with x ≤ 0.20 have been prepared at optimum temperature (950°C–1050 °C) by employing semi-wet technique. The effect of Ba0.90Ca0.10TiO3 (BCT) content on the phase formation, surface morphology, dielectric and piezoelectric properties is systematically investigated and characterized by X-ray diffraction (XRD), Raman Spectroscopy, Field emission Scanning electron micrographs (FE-SEM), Impedance analyzer. XRD analysis shows phase transformation from rhombhohedral to tetragonal with the addition of BCT and the average grain size decreases with BCT content, x. Temperature dependent dielectric behavior exhibits two phase transitions, i.e. depolarization temperature; Td and phase transition temperature; Tm. The phase transitions; Tm tends to diffuse with increasing x and exhibited a broad frequency dependent maximum upto x ≤ 12. Optimum piezoelectric and dielectric properties (i.e., d33 = 165 pC/N, kp = 39%, kt = 47% and k33 = 57%, εr = 1585, tan δ = 0.07) in the studied system have been obtained.

Thermal analysis and crystallization of the glasses inside the BaO–SrO–TiO2–NaPO3 system

The xBa0.5Sr0.5TiO3–(1 − x)NaPO3 (x = 0–0.20 mol%) glasses were prepared by the conventional melt-quenching method. The amorphous state of the samples was verified by X-ray diffraction. The density, molar volume, glass transition temperature (T g), micro-hardness and the crystallization temperature (T c) are determined for each glass. It is found that they depend strongly on the chemical composition of the glasses. The results of the micro-hardness show an increase in the H v parameter with the Ba0.5Sr0.5TiO3 content. The crystallization of glasses is made by submitting samples to heat treatments, and the crystallized phases are identified by XRD. The kinetic of the crystallization is carried out by thermal analysis using DSC technique. The mechanism of crystallization is proposed according to the determined activation energy (E a) and the Avrami parameter (n). The structural approach of the glasses was realized out by IR spectroscopy. This technique has highlighted the co-existence of different phosphate and titanium structural units in the glassy-matrix.

Phase structure, ferroelectric properties, and electric field-induced large strain in lead-free 0.99[(1−x)(Bi0.5Na0.5)TiO3-x(Bi0.5K0.5)TiO3]–0.01Ta piezoelectric ceramics

Lead-free 0.99[(1−x)(Bi0.5Na0.5)TiO3-x(Bi0.5K0.5)TiO3]–0.01Ta piezoelectric ceramics were prepared by a conventional solid-state reaction process. The ferroelectric properties, and strain behaviors were characterized. Increase of the (Bi0.5K0.5)TiO3 content induces a phase transition from coexistence of ferroelectric tetragonal and rhombohedral to a relaxor pseudocubic phase. Accordingly, the ferroelectric order is disrupted significantly with the increase of (Bi0.5K0.5)TiO3 content and the destabilization of the ferroelectric order is accompanied by an enhancement of the unipolar strain, which peaks at a value of 0.35% (corresponding to a large signal d33 of 438pm/V) in samples with 20mol% (Bi0.5K0.5)TiO3 content. Temperature dependent measurements of both polarization and strain from room temperature to 120°C suggested that the origin of the large strain is due to a reversible field-induced nonpolar pseudocubic-to-polar ferroelectric phase transformation.