Coexistence Of Tetragonal Phase Research Articles

Piezoelectric, Dielectric and Ferroelectric Properties of (1−x)(K0.48Na0.52)0.95Li0.05Nb0.95Sb0.05O3-xBa0.5(Bi0.5Na0.5)0.5ZrO3 Lead-Free Solid Solution

The lead-free solid solution $$ (1-x) $$ (K0.48Na0.52)0.95Li0.05Nb0.95Sb0.05O3-xBa0.5(Bi0.5Na0.5)0.5ZrO3 [KNLNS-xBBNZ] with 0.02 < x < 0.05 was successfully prepared by a conventional solid-state route. The effect of BBNZ on the KNLNS phase structure, microstructure and electrical properties was investigated. X-ray diffraction patterns demonstrated a single-phase perovskite-type structure and for 0.02 < x < 0.03 a rhombohedral–tetragonal (R–T) phase coexistence. In addition, the average crystal size greatly decreased with BBNZ doping. Furthermore, the piezoelectric and ferroelectric properties of the KNLNS-xBBNZ ceramics were enhanced at x = 0.02 ( $$ d_{33} $$ = 292 pC/N, $$ - \;d_{31} $$ = 100 pC/N, $$ k_{\rm{p}} $$ = 48%, $$ \varepsilon_{\rm{r}} $$ = 5876, $$ \tan \delta $$ = 0.03) due to a high polarizability at a local level. For x = 0.02, the solid solution showed good thermal stability of the $$ d_{33} $$ piezoelectric constant. As a result, this lead-free solid solution holds potential for applications in electric generators and high-temperature sensors.

Synthesis, Structural, Optical and Dielectric Properties of Nanostructured 0-3 PZT/PVDF Composite Films.

Nanostructured PbZr0.52Ti0.48O3 (PZT) powder was synthesized at 500 °C-800 °C using sol-gel route. X-ray diffraction and Rietveld analysis confirmed the formation of perovskite structure. The sample heat treated at 800 °C alone showed the formation of morphotropic phase boundary with coexistence of tetragonal and rhombohedral phase. The PZT powder and PVDF were used in 0-3 connectivity to form the PZT/PVDF composite film using solvent casting method. The composite films containing 10%, 50%, 70% and 80% volume fraction of PZT in PVDF were fabricated. The XRD spectra validated that the PZT structure remains unaltered in the composites and was not affected by the presence of PVDF. The scanning electron microscopy images show good degree of dispersion of PZT in PVDF matrix and the formation of pores at higher PZT loading. The quantitative analysis of elements and their composition were confirmed from energy dispersive X-ray analysis. The optical band gap of the PVDF film is 3.3 eV and the band gap decreased with increase in volume fraction of PZT fillers. The FTIR spectra showed the bands corresponding to different phases of PVDF (α, β, γ) and perovskite phase of PZT. The thermogravimetric analysis showed that PZT/PVDF composite films showed better thermal stability than the pure PVDF film and hydrophobicity. The dielectric constant was measured at frequency ranging from 1 Hz to 6 MHz and for temperature ranging from room temperature to 150 °C. The composite with 50% PZT filler loading shows the maximum dielectric constant at the studied frequency and temperature range with flexibility.

Magneto-electric coupling and improved dielectric constant of BaTiO3 and Fe-rich (Co0.7Fe2.3O4) ferrite nano-composites

(x)BaTiO3–(1−x)Co0.7Fe2.3O4 (BTO-CFO) magnetoelectric nanocomposite ceramic with x = 0.0, 0.25, 0.50, 0.75, 1.00 were successfully designed and fabricated by sol-gel route. The structural, micro structural, dielectric, ferromagnetic, ferroelectric and magnetoelectric properties of these composites were investigated. The coexistence of tetragonal phase and cubic spinel phase, without any secondary phase in composites is confirmed by the X-ray diffraction measurement. The field emission scanning electron micrograph show well distributed ferrite and ferromagnetic phases in the composites. The energy dispersive X-ray results revealed the purity and stoichiometry of BTO-CFO nanocomposites. The dielectric constant and loss factor of the composites were studied as a function of frequency. The composite sample with x = 0.50, results in higher value of dielectric constant whereas CFO possess lowest value of dielectric constant. The magnetization hysteresis (M−H) loop of the composites show ferromagnetic behavior with saturation magnetization values, Ms varies from 15 to 67.68 emu/g and coercive field Hc from 1538 to 1862 Oe. All the composites exhibit typical ferroelectric hysteresis loops indicating the presence of spontaneous polarization. The magnetoelectric voltage coefficient increases linearly with increases in applied d.c. magnetic bias field up to 8 KOe. The maximum value of magnetoelectric voltage coefficient, αME=7.7 mV/cm Oe for BTO-CFO composite having 25% ferrite and 75% ferroelectric content. The high ME voltage coefficient of BTO-CFO composite may be suitable for storage device application.

Pyroelectric properties of (Ba1-xCdx)(Zr0.13Ti0.87)O3 ferroelectric ceramics in polymorphic state

Ceramic compositions of (Ba1-xCdx)(Zr0.13Ti0.87)O3 with x = 0, 0.02, 0.04 and 0.06 exhibit a layered microstructure and enhanced grain growth (~ 50 µm for x = 0.06). The XRD and Raman measurements reveal the coexistence of rhombohedral, orthorhombic and tetragonal phase, and with increase in Cd content the rhombohedral phase fraction increases significantly (10–56%) whereas the phase fraction of tetragonal decreases (62–14%). Pyroelectric coefficient (p) increases with Cd content and a large value of p ~ 1841 μCm−2 K−1 is obtained for x = 0.06. Current responsivity Fi is maximum (~ 849 pmV-1) for x = 0.02, whereas the voltage responsivity Fv (~45 ×10−3 m2 C−1), detectivity Fd (~48 μPa−1/2) and thermal energy harvesting figure of merit Fe* (~34 pJ−1 m3) are maximum for x = 0.06. Ease of polarization rotation in the polymorphic state due to the coexistence of rhombohedral, orthorhombic and tetragonal phases, and a large ceramic grain size contribute to the strong pyroelectric response.

Structural evolution and dielectric properties of Nd and Mn co-doped BaTiO3 ceramics

(Ba1−xNdx) (Ti0.97Mn0.03)O3 (BNTM) (x = 0.01, 0.02, 0.04, 0.06) ceramics were prepared using a conventional cold-pressing ceramic technique. The structure, valence state and dielectric properties were investigated using XRD, RS, SEM, TEM, EPR, and dielectric temperature and frequency measurements. XRD, RS analysis coupled with SEM and TEM observations indicate that the samples have a coexistence of tetragonal and hexagonal phase at room temperature as x ≤ 0.02 and become a single phase in the tetragonal as x = 0.04 and in the cubic as x = 0.06 (air-sintered, 1400 °C/12 h). It reveals that Nd3+ ions can suppress hexagonal phase effectively and benefit the formation of single-phase ceramics. Improvement of dielectric properties is accompanied by the structural evolution. Particularly a cubic ceramic with x = 0.06, the dielectric-peak temperature is found to shift to room temperature, meeting the EIA Y5V specification with tan δ < 0.04. Up to x = 0.04, the phase transition remains first order. The valence state of Mn ions was analyzed by EPR. It is found that Mn ions transform from high valence (+3 and + 4) to low valence (+2) with the increase of Nd concentration, and all of the Mn ions exist as Mn2+ when x = 0.06. The unit cell volume and dielectric-peak temperature of BNTM decrease nonlinearly with increasing x, which can be ascribed to the incorporation of Nd ions and the formation of 2NdBa·−MnTi″ donor-acceptor defect complexes.

Enhanced piezoelectric properties in (Ba1-xCax)(Ti0.90Sn0.10)O3-0.08Dy2O3 lead-free ceramics

(Ba1-xCax)(Ti0.90Sn0.10)O3-0.08Dy2O3 ceramics (BCTSD-x, x = 0.02–0.10) were fabricated by conventional solid state sintering method. The effect of Ca2+ ions addition on the phase structure, microstructure, and electric properties of ceramics were studied. X-ray diffraction analysis reveals the replacement of Ba2+ ions in the perovskite structure by Ca2+ ions. Rhombohedral phase and tetragonal phase coexist in the composition with x = 0.06–0.10. Both d33 and Kp of the ceramics increase with increasing Ca concentration, and attain maximum values of 675 pC/N and 55.0%, respectively, for x = 0.06. All the ceramics present typical diffuse phase transition behavior, and the feature is not sensitive to the amount of Ca2+ ions.

Polyvinylpyrrolidone modified barium zirconate titanate /polyvinylidene fluoride nanocomposites as self-powered sensor

Highly flexible biocompatible nanocomposites comprising of Polyvinylpyrrolidone (PVP) modified Barium Calcium Zirconate Titanate (BCT-BZT) /Polyvinylidene fluoride (PVDF) were fabricated. The crystalline BCT-BZT powders were synthesized by a simple sol-gel method. Rietveld refinement analysis confirmed the coexistence of orthorhombic and tetragonal phase in the synthesized powders. The structural, dielectric and ferroelectric properties of the composites were analysed. Addition of PVP modified BCT-BZT powders was observed to enhance the polar phase in PVDF matrix. The piezoelectric output response as a function of different weight percentage of ceramic powders in the PVDF matrix was investigated. The optimal device with 60 wt% PVP modified BCT-BZT powders exhibited maximum peak to peak voltage of 23 V when tested for harnessing waste biomechanical energy (human hand palm force). The nanogenerator was easily scaled up to 4 × 4 cm and the stored power was utilized for powering fifty five LEDs. The fabricated device is flexible, light- weight and eco-friendly. Therefore, it can be explored as a potential candidate for application as self powered sensor.

Dielectric properties of (K0.5Na0.5)NbO3–(Bi0.5Li0.5)ZrO3 lead-free ceramics as high-temperature ceramic capacitors

(1 − x)K0.5Na0.5NbO3–x(Bi0.5Li0.5)ZrO3 (labeled as (1 − x)KNN–xBLZ) lead-free ceramics were fabricated by a solid-state reaction method. A research was conducted on the effects of BLZ content on structure, dielectric properties and relaxation behavior of KNN ceramics. By combining the X-ray diffraction patterns with the temperature dependence of dielectric properties, an orthorhombic–tetragonal phase coexistence was identified for x = 0.03, a tetragonal phase was determined for x = 0.05, and a single rhombohedral structure occurred at x = 0.08. The 0.92KNN–0.08BLZ ceramic exhibits a high and stable permittivity (~ 1317, ± 15% variation) from 55 to 445 °C and low dielectric loss (≤ 6%) from 120 to 400 °C, which is hugely attractive for high-temperature capacitors. Activation energies of both high-temperature dielectric relaxation and dc conductivity first increase and then decline with the increase of BLZ, which might be attributed to the lattice distortion and concentration of oxygen vacancies.

Morphology of phase-separated VO2 films deposited on TiO2-(001) substrate

The basic morphology of phase-separated VO2 films, in which the tetragonal (metallic) phase coexists with the monoclinic (insulating) phase, was studied using transmission electron microscopy. While the phase transformation temperature in an unstrained crystal is approximately 340 K, it was observed that at 298 K, elastic strain (caused by lattice mismatch with the TiO2-(001) substrate) stabilized the tetragonal phase near the VO2/TiO2 boundary. The observed zig-zag-shaped interface of the tetragonal phase was explained by the crystallographic orientation relationship between the tetragonal and monoclinic phases. The observations provide valuable information for future applications of VO2 films.

Fatigue endurance enhancement of Sn-doped Pb(Lu1/2Nb1/2)O3-PbTiO3 ceramics.

Several mechanisms and methods have been proposed to study the nature of electric fatigue in ferroelectric materials with perovskite structure, including defect agglomeration, field screening and the reorientation of defect dipoles. To ascertain the effect of defect, defect dipoles in particular on the fatigue behavior in perovskite ferroelectrics, 0.51Pb(Lu1/2Nb1/2)O3–0.49PbTi1−xSnxO3 ferroelectric ceramics were fabricated in this work. It is found that the fatigue endurance has been enhanced after Sn-doping. An abnormal strong self-rejuvenation of polarization was also detected for un-poled and un-aged samples resulting from the reorientation of defect dipoles. The defect dipoles were determined by the confirmed change of the valence of Sn ions and the appearance of oxygen vacancies. The reorientation was also confirmed by the internal bias of P–E hysteresis loops during the fatigue process. With more Sn doped into the matrix, the symmetry changed from a coexistence of rhombohedral and tetragonal phase to a rhombohedral phase. The remnant polarization decreased, while the coercive field first decreased then increased as x increased, which resulted from the composition variance and the effect of defect dipoles. It indicates that the defect dipoles play an important role in the electric fatigue behavior of Sn-doping PLN–PT ceramics.

Effects of nano-sized BCZT on structure and electrical properties of KNN-based lead-free piezoceramics

The (1 − x)(Li0.03Na0.5K0.47)(Nb0.92Sb0.05Ta0.03)O3–xBa0.85Ca0.15Zr0.1Ti0.9O3 (LNKNST–BCZT, x = 0, 0.5, 1.5, 2.5, and 3.5%) lead-free piezoceramics were synthesized by the conventional solid-state reaction method with adding nano-sized Ba0.85Ca0.15Zr0.1Ti0.9O3 (BCZT) powder to investigate their influences on crystal structure and electrical properties. The X-ray diffraction (XRD) analysis reveals that all the sintered LNKNST–BCZT ceramics exhibit pure perovskite structure with the mainly rhombohedral (R) phase or the coexistence of rhombohedral (R) phase and tetragonal (T) phase. The composition of the LNKNST–1.5%BCZT ceramics locates around the critical point, i.e., the ceramics changing from the coexistence of rhombohedral (R) phase and tetragonal (T) phase to purely rhombohedral (R) phase, and presents the most densified microstructure morphology, which can be confirmed further by the field emission scanning electron microscope (FESEM) observation. There are two dielectric anomalies in the temperature dependent dielectric properties curves of the LNKNST–BCZT ceramics, which correlate with the ferroelectric rhombohedral (R) phase changing to the ferroelectric tetragonal (T) phase, and then to the paraelectric cubic (C) phase. Both the Curie–Weiss law and the power law fittings confirm the diffuse phase transition ferroelectrics characteristic of the LNKNST–1.5%BCZT ceramics, which is considered as correlating with the polar nanoregions (PNRs). Due to the densification effect caused by the chosen amount of nano-sized BCZT doping and the construction of R–T polymorphic phase boundary, the LNKNST–1.5%BCZT ceramics exhibit the best ferroelectric and piezoelectric properties. The complex impedance spectroscopy analysis confirms that the extrinsic electrical conduction mechanism at high temperatures is dominated by the oxygen vacancies induced by the evaporation of the alkali metals during sintering.

Columnar structural FePt films with good perpendicular anisotropy induced by tuning the crystal structure of doping materials

Crystalline ZrO2 doping would degrade the perpendicular texture of FePt films due to the epitaxial growth of FePt (200) textured phase on the tetragonal (002) textured ZrO2. In the present paper, crystalline HfO2 was used to replace crystalline ZrO2 as the crystalline doping material and FePt media with columnar structure and good perpendicular anisotropy were achieved. It is found that HfO2 crystallized on TiON intermediate layer presented the coexistence of both monoclinic and tetragonal phase. The extremely large lattice mismatch strain (around 25–28%) between FePt and HfO2 would prohibit the (200) or (001) epitaxial growth of FePt phase on HfO2. This would cause FePt-HfO2 film to have better (001) texture and perpendicular anisotropy compared to FePt-ZrO2 films. By tuning the crystal structure of doping crystalline phase material, columnar structural FePt films with better perpendicular anisotropy could be obtained, which may offer a method for the application of FePt media in heat assisted magnetic recording.

A novel ((Bi0.5Na0.5)0.94Ba0.06)1-x (K0.5Nd0.5)xTiO3 lead-free relaxor ferroelectric ceramic with large electrostrains at wide temperature ranges

Novel ((Bi0.5Na0.5)0.94Ba0.06)1-x(K0.5Nd0.5)xTiO3(x = 0.0, 0.02, 0.04, 0.06) lead-free ceramics (BNBT–xKN) were prepared by the solid-state reaction method. The effects of A-site (K0.5Nd0.5)2+ complex-ion substitution on their phase structure, dielectric, piezoelectric, and electromechanical properties were studied. The X-ray diffraction results indicate that all compositions are located in the morphotropic phase boundary (MPB) region where the tetragonal phase coexists with the rhombohedral phase. In addition, as the KN content increases, the ferroelectric order transform to relaxor order, which is characterized by a degeneration of maximum polarization, remnant polarization and correspondingly adjusts the ferroelectric-relaxor transformation temperature (TF-R) to room temperature. Interestingly, the disruption of ferroelectric phase caused a significant improvement of strains. A maximum strain of ~ 0.52% corresponding to normalized strain of ~ 612pm/V appeared at 85kv/cm for the x = 0.04 composition. Particularly, the composition of x = 0.04 exhibited high electrostrains of temperature insensitivity, which remained above 0.4% and kept within 10% from ambient temperature up to 110°C. It can be ascribed to the coexistence of non-ergodic and ergodic states in the relaxor region. As a result, the systematic investigations on the BNBT–xKN ceramics can benefit the developments of temperature-insensitive “on-off” actuators.

Structure and piezoelectric properties of (Ba1−xCax)(Ti0.95Hf0.05)O3 lead-free ceramics

Lead-free (Ba1−xCax)(Ti0.95Hf0.05)O3 (x=0.04–0.14) (BCHT) ceramics with good piezoelectric properties were successfully prepared using solid state reaction method. The structural and electrical properties of the BCHT ceramics were systematically studied. The polymorphic phase transitions (PPT) from orthorhombic phase to tetragonal phase shifts towards low temperature with increasing Ca contents, and the PPT can be obtained at room temperature (RT) in the composition range of 0.08–0.10 for the BCHT ceramics. The tetragonality of the BCHT ceramics at PPT is increased after poling treatment as depicted in the XRD patterns and Raman spectroscopy. The BCHT ceramics at x=0.08 exhibit good piezoelectric properties (d33=380 pC/N, kp=50% and Smax=0.19% under the applied electric field of 50kV/cm) and ferroelectric property (Pr=13.4μC/cm2), due to the coexistence of tetragonal phase and orthorhombic phase. The aging rate of d33 values from 20°C to 90°C is lower than 20% in this work, indicating that the BCHT ceramics have good temperature stability. The high piezoelectric properties with good temperature stability indicate that the BCHT ceramics are promising candidates as lead-free piezoelectric ceramics.

Effects of sintering temperature and composition on dielectric, ferroelectric, and magnetoelectric properties of BaTiO3–BiFeO3 solid solutions

A series of (1–x)BaTiO3–xBiFeO3 ( (1–x)BT–xBFO) multiferroic ceramics with the composition of x from 0 to 0.07 have been synthesized. The effects of the sintering temperature and composition on the crystal structure, microstructure, dielectric, ferroelectric, and magnetoelectric properties of the ceramics were investigated. With an increase of BFO content, the phase structure of the as prepared ceramics changed from tetragonal to cubic at a threshold value of x = 0.03. The region of the morphotropic phase boundary lies in the composition of x from 0.03 to 0.05, in which the tetragonal and cubic phase coexist. The dielectric constants have been greatly increased from 812 for pure BaTiO3 to 2667 of the composition 0.96BT–0.04BFO at the 10kHz, which have been improved about 328%. The ceramics with the composition of x = 0.04 exhibited excellent ferroelectric characteristics, in which the remnant polarization Pr is 16.74μC/cm2. The maximum magnetoelectric coefficient is 298.8mV/cmOe for the material with x = 0.04 at 900kHz and 1kOe.

Fabrication and Characterization of Carbonized Rice Husk/Barium Titanate Nanocomposites

Carbon materials were prepared by carbonizing rice husk (RHs) at 2500°C. Few- and multi-layer graphene were obtained from this carbonization process. Barium titanate (BTO) nanoparticles were fabricated by using sol-gel method. Then, the BTO nanoparticles were grafted onto the surface of carbonized rice husk (CRH) to fabricate CRH/BTO nanocomposites. The nanocomposites were characterized using scanning transmission electron microscopy (STEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), Raman measurement, and X-ray photoelectron spectroscopy (XPS). Based on the broadening of (1 1 0) peak from XRD result, the average crystalline size of BTO nanoparticles were calculated to be 16.5 nm. Coexistence of cubic and tetragonal phase of BTO nanoparticles is expected, based on the XRD and Raman results. From XPS result, carbon, barium, titanium, and oxygen peaks were also observed. The combination of CRH with BTO can integrate the properties of these two components to form nanocomposites for broad applications.

Structural and functional characterisation of KNNS–BNKZ lead-free piezoceramics

ABSTRACTPromising piezoelectric properties have been reported recently for lead-free 0.96(K0.48Na0.52Nb0.95Sb0.05)–0.04Bi0.5(Na0.82K0.18)0.5ZrO3 (KNNS–BNKZ) ceramics. The presence of coexisting rhombohedral and tetragonal phases is thought to play a key role in their functional properties, but a thorough understanding is currently lacking. In this experiment, (1−x)KNNS–(x)BNKZ ceramics with x = 0–0.05 were prepared by the mixed-oxide method. High-resolution synchrotron X-ray powder diffraction (SXPD) measurements reveal that the addition of BNKZ into KNNS ceramics leads to an increase in the rhombohedral–orthorhombic phase transition temperature (TR−O) and a decrease in the orthorhombic–tetragonal phase transition temperature (TO−T) leading to orthorhombic–tetragonal and rhombohedral–tetragonal phase coexistence at room temperature for compositions with x = 0.02 and 0.04, respectively. By combining the SXPD results with microstructure, evidence is also found for the occurrence of chemical heterogeneity, which could provide an additional means to control the functional properties. The structural observations are correlated with changes in the dielectric and ferroelectric properties.

Dielectric and ferroelectric properties of Ba0.87Ca0.10La0.03Ti1-xSnxO3 lead-free ceramics

Ba0.87Ca0.10La0.03Ti1-xSnxO3 (BCLTS) piezoelectric lead-free ceramics were fabricated by conventional solid-state sintering process at 1480 °C. The effects of Sn4+ substitution on microstructure and electrical properties of the ceramics were researched. All samples show a pure perovskite structure with no secondary phase, and the coexistence of orthorhombic phase and tetragonal phase in the composition range of x = 0.06–0.10 is identified in the XRD pattern. Average grain size decreases with the increase of Sn content in the BCLTS samples. The BCLTS ceramics exhibit excellent piezoelectric properties and ferroelectric properties with d33 = 501pC/N and kp = 45.6% at x = 0.10, and Pr = 9.87 μC/cm2 at x = 0.06. The analysis on the temperature dependence of dielectric permittivity approved the diffuse relaxor ferroelectric feature for all the BCLTS samples.

Large electro-strain response of La3+ and Nb5+ co-doped ternary 0.85Bi0.5Na0.5TiO3-0.11Bi0.5K0.5TiO3-0.04BaTiO3 lead-free piezoelectric ceramics

La3+ and Nb5+ co-doped 0.85Bi0.5Na0.5TiO3-0.11Bi0.5K0.5TiO3-0.04BaTiO3 (BNT-BKT-BT) samples were prepared through conventional solid oxide route, and the effects of doping ions on the phase structure, electrical properties, and electro-strain behavior were investigated. The XRD results showed that La3+ and Nb5+ co-dopant induced a phase transition from coexistence of ferroelectric tetragonal and rhombohedral phase to a pseudocubic phase. With increasing dopant content, the normal ferroelectric-to-ergodic relaxor (FE-to-ER) transition temperature (TF-R) decreased down from 120 °C to room temperature (RT), even below RT. A large unipolar strain of 0.34% (d33∗ = Smax/Emax = 680 pm/V) was achieved under 5 kV/mm and the largest electro-strain of 0.46% was achieved under an applied electric field of 7.5 kV/mm at RT for x = 0.0050. Temperature dependence of both polarization loops and bipolar strain curves from room temperature to 160 °C were also studied, and the results suggested that the origin of the large strain is attributed to a reversible nonpolar isotropic ergodic relaxor state to polar anisotropic ferroelectric phase transition.

Novel rhombohedral and tetragonal phase boundary with high T C in alkali niobate ceramics

We design a new composition to establish rhombohedral and tetragonal phase coexistence in alkali niobate ceramics. The composition of (1−x)[0.94(K0.48Na0.52)NbO3–0.045Bi0.5Na0.5ZrO3−0.015CaTiO3]–xLi0.2Na0.8NbO3 has been synthesized by conventional solid-state reaction method. XRD patterns and curves of permittivity versus temperature show that the phase of this kind of perovskite structure ceramics convert tetragonal phase (x ≤ 0.4) into rhombohedral phase (x ≥ 0.5), and the rhombohedral and tetragonal (R-T) phases coexistence has been confirmed at x = 0.425 ~ 0.475. Around this phase boundary, the ceramics with x = 0.425 show an optimum piezoelectric properties (d 33 ~ 178 pC/N and k p ~ 38.5%) with high T C ~ 400 °C. Moreover, the ceramics exhibited strong temperature stability. This work exhibits obviously different piezoelectric properties from other R-T coexistence systems in KNN-based ceramics, the underlying physical mechanism has been discussed. It is believed that this method could promote the further development of alkali niobate ceramics.