Tetragonal BF-xPT-0.1BZT ceramics with high Curie temperature and large piezoelectric constant

Obtaining both high Curie temperature and large piezoelectric constant simultaneously is of great significance for the application of actuators and sensors. In this research, the piezoelectric ceramics of (0.9-x)BiFeO₃-xPbTiO₃-0.1Ba(Zr_0.5Ti_0.5)O₃ (BF-xPT-0.1BZT, x = 0.29, 0.30, 0.31 and 0.32) were fabricated by the traditional solid-state reaction method. BF-xPT-0.1BZT ceramics exhibit the tetragonal perovskite structure without detectable second phases, and the tetragonality c/a ratio and the tolerance factor of ceramics are about 1.03 and 0.98, respectively. SEM images reveal that ceramics are well densified with the average grain size of 5–12 μm. The Curie temperature T_C of BF-xPT-0.1BZT ceramics is about 490–509 °C, slightly changing with the variation of PT content. The excellent comprehensive dielectric and piezoelectric properties are achieved for BF-0.31PT-0.1BZT ceramics with dielectric constant ε_r (1 kHz), tanδ, piezoelectric constant d₃₃ and T_C of 1001, 0.008, 230 pC/N and 509 °C, respectively. The significant enhancement of piezoelectric constant in the x = 0.31 sample is attributed to the enlargement of grain size. Moreover, the d₃₃ and the planar coupling coefficient k_p remain stable in the elevated temperature range of 200–400 °C, and the fluctuations are only 2% /℃ and 0.007% /℃, respectively, both of which are superior to that of BS-PT based piezoelectric ceramics. Our results indicate that BF-0.31PT-0.1BZT ceramics with high T_C, large d₃₃ and good thermal stability possess great potential for high temperature piezoelectric applications.     

Investigation of dielectric and piezoelectric properties in Pb(Ni1/3Nb2/3)O3–PbHfO3–PbTiO3 ternary system

The dielectric and piezoelectric properties were investigated in the (1 ? x)Pb(Hf_1?yTi_y)O₃–xPb(Ni_1/3Nb_2/3)O₃ (PNN–PHT, x = 0.05–0.50, y = 0.55–0.70) ternary system. The morphotropic phase boundary (MPB) was determined by X-ray powder diffraction analysis. Isothermal map of Curie temperature (T_C) related to the compositions in the phase diagram was obtained. The optimum dielectric and piezoelectric properties were achieved in ceramics with the MPB compositions, with the maxima values being on the order of 6000 and 970pC/N, respectively. Rayleigh analysis was used to study the extrinsic contribution (domain wall motion) in PNN–PHT system, where the extrinsic contribution was found to be ～30% for composition 0.49PNN–0.51PHT(30/70), showing a high nonlinearity.     

Room temperature constructing rhombohedral-tetragonal phase boundary in novel (Bi,Na)(Zr,Ti)O3 modified (K,Na)(Nb,Sb)O3 ceramics: Phase structure,defect and piezoelectric performance

Lead-free (1-x)(K_0.5Na_0.5)(Nb_0.96Sb_0.04)O₃-x(Bi_0.5Na_0.5)(Zr_0.8Ti_0.2)O₃ ceramics (abbreviated as (1-x)KNNS-xBNZT, x = 0, 0.01, 0.02, 0.03, 0.035 and 0.04) were synthesized by the solid-state method, and the dependence of phase evolution, microstructure, oxygen vacancy defect and electrical properties on compositions were carefully investigated. All ceramics had a pure perovskite structure and a dense microstructure. The phase transition temperatures (T_R-O and T_O-T) of the ceramics were adjusted by adding BNZT, and the rhombohedral-tetragonal (R-T) phase coexistence boundary was successfully constructed at room temperature when x = 0.03, the excellent piezoelectric performance (d₃₃ ～ 323 pC/N, k_p ～ 0.372) and high Curie temperature (T_C ～ 276 °C) have been achieved at this time. The grain size of the ceramics showed a strong difference on x content, and the maximum relative density value of 95.42% was obtained. The domain structure characterized by PFM confirmed that the ceramics possess small-sized nano-domains and complex domains at x = 0.03, which are the origin of enhanced piezoelectric properties. Moreover, the oxygen vacancy defect that can pin the domain walls was increased with the addition of (Bi_0.5Na_0.5)(Zr_0.8Ti_0.2)O₃. As a result, the doping with BNZT can significantly affect the phase structure and electrical properties of the ceramics, indicating that the (1-x)KNNS-xBNZT ceramics system with a R-T phase boundary is a promising lead-free piezoelectric material.     

Normal-relaxor ferroelectric phase transition induced morphotropic phase boundary accompanied by enhanced piezoelectric and electrostrain properties in strontium modulated Bi0.5K0.5TiO3 lead-free ceramics

In this work, (Bi_0.5K_0.5)_1-xSr_xTiO₃ compositions (x = 0.03∼0.18) are designed to clarify the role of normal-relaxor ferroelectric phase transition and morphotropic phase boundary on dielectric, piezoelectric and electrostrain properties. With increasing strontium content, tetragonal distortion decreases and tetragonal and pseudocubic phases coexist in 0.09 ≤ x ≤ 0.15 compositions; the spontaneous phase-transition temperature and curie temperature decrease, as certified by phase-structure, dielectric properties and Raman spectra analysis. Optimized piezoelectric constant ∼106 pC/N and electrostrain ∼0.17 % are obtained for (Bi_0.5K_0.5)_0.88Sr_0.12TiO₃ composition. Piezoelectric force microscopic technique is exploited to clarify the origin of enhancement in macroscopic performances. Increase in temperature enhances ferroelectric performance and a large strain value ∼0.25 % with low hysteresis ∼27 % are obtained at 140 °C for the optimized composition, which are believed to originate from electric-field induced relaxor-to-ferroelectric phase transition with thermally-activated reduced energy barriers. This work clearly demonstrates that lead-free Bi_0.5K_0.5TiO₃-based ceramics are another promising bismuth-based species in applications of piezoelectric sensors and actuators.     

Improved ferroelectric properties of BiFeO3-based piezoelectric ceramics through morphotropic phase boundary construction

The ceramic (1-x)BiFe_0.985Sc_0.015O₃-xBaZr_0.2Ti_0.8O₃ + 1mol% MnO₂ (x = 0.20, 0.25, 0.30, 0.35) (BFS-xBZT) was synthesized using the traditional ceramic sintering method. The components of the ceramic were determined by constructing a morphotropic phase boundary (MPB) which consists of rhombohedral (R) and tetragonal (T) phases (0.24≤ x ≤ 0.26). With the accumulation of BZT content, relax behaviors were observed by dielectric properties measurements. At the MPB, the crystal structures of the R phase and T phase change abruptly. The distortion degree of the R phase increases, and the differences between a and c of the T phase decrease. An enhanced ferroelectricity Pr of ~27.8 μC/cm² and apex piezoelectric coefficient d₃₃ of 131 ± 4 pC/N are obtained near the MPB (x = 0.25), due to the R-T phase coexistence near room temperature. The results show that BFS-xBZT ceramics could be a candidate for lead-free piezoelectric ceramics at high operating temperatures.     

Improved temperature stability and high piezoelectricity in lead-free barium titanate-based ceramics

To achieve high piezoelectricity and the corresponding good temperature stability of BaTiO₃ (BT) ceramics, a new system of (1-x-y) BaTiO_3?–?yCaTiO_3?–?x(BaZr_1-zHf_z)O₃ (BT-yCT-xBZH_z) was designed. The O-T phase boundary was observed at 0.065?≤?x?≤?0.085, 0.08?≤?y?≤?0.12 and 0?≤?z?≤?1.0 near room temperature. Due to the O-T phase boundary, the enhancement of electrical properties (d₃₃?=?500 pC/N, k_p?=?0.52, P_r?=?14.0?μC/cm² and ε_r?=?2800), large strain (～0.23%) and d₃₃^*?=?1100?pm/V (10?kV/cm) can be obtained. Moreover, temperature-dependent electrical properties were investigated in detail, and a reliable performance was realized due to high T_C (>100?°C). The d₃₃^* was demonstrated to be temperature-insensitive from 16?°C to 60?°C (varying less than 7%), which is superior to the reported BT-based ceramics. Besides, d₃₃ and P_r fluctuate less than 22% in this temperature range, also showing an usable stability. We believe that this work can be beneficial to facilitate an increasing adoption of lead-free BT-based piezoceramics for practical applications.     

Depolarization temperature and piezoelectric properties of (Bi1/2Na1/2)TiO3–(Bi1/2Li1/2)TiO3–(Bi1/2K1/2)TiO3 lead-free piezoelectric ceramics

The phase transition temperature and piezoelectric properties of x(Bi_1/2Na_1/2)TiO₃–y(Bi_1/2Li_1/2)TiO₃–z(Bi_1/2K_1/2)TiO₃ [x + y + z = 1] (abbreviated as BNLKT100y–100z) ceramics were investigated. BNLKT100y–100z ceramics were prepared by conventional ceramic fabrication. The depolarization temperature T_d was determined by the temperature dependence of the dielectric and piezoelectric properties. This study focuses on the effect of Li¹⁺ and K¹⁺ ions on T_d and the piezoelectric properties of BNT ceramics. BNLKT100y–100z (y = 0–0.08) has a morphotropic phase boundary (MPB) between rhombohedral and tetragonal phases at z = 0.18–0.20, and high piezoelectric properties were obtained at the MPB composition. The piezoelectric constant d₃₃ increased with increasing y; however, T_d decreased above y = 0.06. The d₃₃ and T_d values of BNLKT4-20 and BNLKT8-20 were 176 pC/N and 171 °C, and 190 pC/N and 115 °C, respectively.     

Effects of CuO addition on the sinterability and electric properties in PbNb2O6-based ceramics

PbNb₂O₆ (PN)-based ceramics with tungsten bronze structure are promising piezoelectric materials in high-temperature devices such as piezoelectric vibration transducers. However, the PN-based ceramics usually exhibit a low bulk density, which greatly limits their practical applications. In this work, CuO was used as the sintering aid to form a liquid-phase bridge, leading to an obvious increase of the bulk density of PN-based ceramics by 11% (from 5.25 to 5.85 g cm⁻³) and the improvement of the piezoelectric constant (d₃₃) (from 168 to 190 pC/N) and the Curie temperature (T_C) from 367 to 395 °C. The positive influence of CuO on densification has been proved by SEM and fracture toughness. The XRD patterns confirmed that there was no secondary phase introduced by CuO addition. The Raman spectra revealed that part of Cu²⁺ ions has probably diffused into host lattice of the PN and preferred to occupy on A-sites. These results not only demonstrate the high potential of the CuO added PN-based ceramics for high-temperature piezoelectric applications, but also reveal the corresponding structure-properties relationship as well as provide a way to improve the sinterability, d₃₃, and T_C simultaneously.     

Phase transition induced morphotropic phase boundary behavior and the electric properties in strontium modulated Bi4.5Na0.5Ti4O15 lead-free ceramics

Lead-free (Bi_0.5Na_0.5)_1-xSr_xBi₄Ti₄O₁₅ ceramics (x = 0–0.9) are fabricated by solid state reaction process. XRD analysis shows the symmetry divergence from tetragonal to orthorhombic phase accompanied by morphotropic phase boundary with increasing strontium content. Raman spectra confirm the incorporation of strontium into (Bi_2.5Na_0.5Ti₄O₁₃)^2- layers. SEM graphs exhibit the typical plate-like morphology with regular variation of grain size and crystallization as strontium increases. Multistage ferroelectric transition is observed with x = 0.2–0.4. Piezoelectric performance measurements present the well thermal stability at x = 0.4. The dielectric properties display a shifting of Curie temperature towards low temperature with increasing strontium ions. It can be due to the crystal lattice distortion by larger radius of strontium and the increasing tolerance factor. ac conductivity and impedance measurements suggest that electron hopping mainly contributes to the low temperature region. Ionization conductivity by oxygen vacancy migration including first-ionization and double-ionization plays the dominating role in the middle and high temperature region. The controllable properties indicate the potential applications for electric devices of (Bi_0.5Na_0.5)_1-xSr_xBi₄Ti₄O₁₅ ceramic.     

Interrelation between lattice structures and polarization in high Curie temperature piezoelectric Na0.5Bi4.46Ce0.04Ti4-xCoxOy ceramics

Some lead-free piezoelectrics cannot meet the requirement for application in extremely harsh high-temperature surroundings. In this work, an enhanced piezoelectric performance with high piezoelectric coefficient (d₃₃) and high Curie temperature (T_c) has been achieved by replacing the Ti⁴⁺ with the Co³⁺ in Na_0.5Bi_4.46Ce_0.04Ti_4-xCo_xO_y ceramics. The introduction of Co³⁺ decreases the B–O bond lengths, leading to the shrinkage of BO₆ octahedra and lattice volume. The electron localization degree of B–O bond and the polarity of the BO6 octahedra were improved by diminution of lattice volume concomitantly, which were indicated by the first principle calculations. Therefore, an enhanced piezoelectric coefficient of 22 pC/N and high T_c of 690.2 °C have been realized in Na_0.5Bi_4.46Ce_0.04Ti_4-xCo_xO_y ceramics with x = 0.02 mol. Our work gives a good paradigm to design superhigh temperature piezoelectric devices for practical application in extremely harsh circumstances.     

Pb(In1/2Nb1/2)O3-PbZrO3-PbTiO3 ternary ceramics with temperature-insensitive and superior piezoelectric property

The development of ferroelectric ceramics with both large piezoelectric responses and broad service temperature range is still a key challenge for practical applications due to the so-called d₃₃-T_C trade-off. Here we report the strategy to utilize the synergistic contribution of morphotropic phase boundary and enhanced local structural heterogeneity, in which an excellent piezoelectric coefficient d₃₃ of 680 pC/N and a high Curie temperature of 330 ℃ are simultaneously achieved in Sm modified 0.25PIN-0.325PZ-0.425PT ceramics. The underlying mechanism responsible for the high dielectric and piezoelectric properties is studied based on cryogenic dielectric measurement and Rayleigh analysis. Of particular interest is that, a high field-induced strain of 0.19% is achieved in 0.25PIN-0.32PZ-0.43PT at electric field of 20 kV/cm, corresponding to a piezoelectric d₃₃ * of 945 pm/V, showing an excellent temperature stability with minimal variation of 7% up to 310 °C. This work demonstrates the introduction of high temperature end members and rare earth doping are conducive to ferroelectric solid solutions with desired broad usage temperature range and superior piezoelectric properties, which will greatly benefit high temperature actuator applications.     

BiScO3-PbTiO3 piezoelectric ceramics with Bi excess for energy harvesting applications under high temperature

0.36BiScO₃-0.64PbTiO₃ ceramic is a competitive piezoelectric material even though it contains lead and volatile Bi contents. It contains a relatively decreased lead content compared to that of the Pb(Zr,Ti)O₃ system but it has similar piezoelectric properties with high Curie temperature. However, due to the very volatile component of Bi the 0.36BiScO₃-0.64PbTiO₃ system has Bi-deficient composition. Therefore, in order to compensate for deficient Bi contents in the 0.36BiScO₃-0.64Pb,TiO₃ system, excess 0.005, 0.01, 0.015 and 0.02 mol of Bi were added to the ceramics to enhance the piezoelectric properties for the first time. By employing excess Bi addition, the piezoelectric charge coefficient, electromechanical coupling factor, output open circuit voltage, and generated output power density were improved from 417 pC/N, 51.48%, 19.69 V and 0.28 mJ/cm³ to 452 pC/N, 52.25%, 26.93 V and 0.48 mJ/cm³. We expect that piezoelectric properties of 0.36BiScO₃-0.64PbTiO₃ ceramics were improved by adding Bi excess.     

Phase transitional behavior and piezoelectric properties of BiYbO3–Pb(Ti0.5Zr0.5)O3–LiNbO3 ceramics

Perovskite (1 − x)(0.06BiYbO₃–0.94Pb(Ti_0.5Zr_0.5)O₃)–xLiNbO₃ (BYPTZ-LN) ceramics were synthesized by the conventional ceramic processing. The effect of LiNbO₃ on the microstructure and piezoelectric properties was investigated. The perovskite phase and the Yb₂Ti₂O₇ pyrochlore phase are coexisting in the BYPTZ-LN ceramics sintered at 1140 °C. The material with perovskite structure is tetragonal at x ≤ 0.04 and becomes single rhombohedral at x ≥ 0.08. A morphotropic phase boundary between rhombohedral and tetragonal phases is found in the composition range 0.04 ≤ x ≤ 0.08. Analogous to Pb(Zr,Ti)O₃, the piezoelectric and electromechanical properties are enhanced for compositions near the morphotropic phase boundary. Piezoelectric constant d₃₃values reach 290–360 pC/N. Electromechanical coefficients k_p reach 0.38–0.55. The maximum values of d₃₃, k_p and P_r are obstained as x = 0.08, accompanying with the minimum values of Q_m and E_c. The Curie temperature T_c and the maximum value of dielectric constant decrease with increasing LiNbO₃ content. BYPTZ-LN ceramics with the high d₃₃ value and the high thermal-depoling temperatures of >320 °C are obtained.     

Enhanced piezoelectric and ferroelectric properties of BiFeO3-BaTiO3 lead-free ceramics by optimizing the sintering temperature and dwell time

0.7BiFeO₃-0.3BaTiO₃ (BFO-0.3BT) ceramics were prepared to uncover the impacts of sintering temperature (T_S) and dwell time (t_d) on the microstructure and electrical properties. With increasing the T_S or t_d, the grain sizes increase along with the porosity decreases, which is in favor of the alignment of dipole. However, excess T_S or t_d are inclined to cause the volatilization of Bi₂O₃, which deteriorates piezoelectric properties. Because of the R-T two-phase coexistence, low defect ions concentration and porosity, as well as appropriate grain size, the excellent d₃₃?=?208?pC/N and k_p?=?35.46% as well as P_r?=?28.52?μC/cm² were achieved in BFO-0.3BT ceramics at T_S?=?1000?°C and t_d?=?6?h. In addition,large unipolar strain 0.13% and d₃₃*?=?256.2?pm/V also were obtained in BFO-0.3BT ceramics at T_S?=?1000?°C and t_d?=?6?h. This research indicates that the porosity and defect ion concentration as well as grain size also play an important role in piezoelectric properties in BFO-BT ceramics.     

Excellent temperature stability of strain in PZ-PT-BNT ternary ceramics

Lead-based Pb(Zr, Ti)O₃ ceramics have been widely applied in piezoelectric actuators, and yet high temperature stability and large strain have been pursued for further application. In this work, a novel PbZrO₃–PbTiO₃-(Bi_0.5Na_0.5)TiO₃ (PZ-PT-BNT) piezoelectric ceramic is designed and prepared by solid-state route. It is found that the introduction of BNT constituent enhances the relaxation behavior of PZ-PT ceramic, inhibits the abrupt change in dielectric properties near Curie temperature, and increases the proportion of tetragonal phase with high temperature stability. Meanwhile, the patterns of electric domains are intentionally modified by adjusting composition of PZ-PT-BNT. Short and broad electric domains in PZ-PT-0.03BNT ceramic are observed by piezoresponse force microscopy, which are insensitive to temperature and have faster response under electric field, contributing to strain characteristics. As a result, through integrating phase structure and electric domain configuration, a strain of 0.21% and excellent temperature stability where the variation of strain is less than 8% in the temperature range of 25–250 °C are achieved in PZ-PT-0.03BNT ceramic. The findings provide an effective strategy for improving the strain stability of PZ-PT-based piezoelectric ceramics, and demonstrate that PZ-PT-BNT ceramics have potential application prospects in high-temperature piezoelectric actuators.     

PLZST antiferroelectric ceramics with promising energy storage and discharge performance for high power applications

Capacitors are widely used as energy storage elements in electric vehicles (EVs) and pulsed power. At present, it is still challenging to develop capacitor dielectrics with good energy storage and discharge performance. In this work, antiferroelectric (AFE) ceramics (Pb_0.94La_0.04)[(Zr_0.6Sn_0.4)_0.92Ti_0.08]O₃ with enhanced antiferroelectricity were fabricated by a rolling process. The obtained ceramics have a high recoverable energy density of 5.2 J/cm³ and an extremely high efficiency of 91.2% at 327 kV/cm. The ceramics have good energy storage and discharge performance in the temperature range from −40°C to 100°C due to the existence of AFE phase. An energy density of 3.7 J/cm³ can be released at 200 kV/cm in less than 500 ns and the discharge current keeps stable after 1000 charge-discharge cycles. By direct short experiment, a current density of 1657 A/cm², which is the highest result in recently developed AFE ceramics, and a power density of 228 MW/cm³ were achieved. The possibility of using AFEs at low temperature was confirmed. The excellent energy storage and discharge performance prove the great potential of the obtained ceramics in high energy and power density applications.     

A novel piezoelectric ceramic with high Curie temperature and high piezoelectric coefficient

0.02Pb(Sb_1/2Nb_1/2)O₃-0.98Pb_1-xBa_x(Zr_0.53Ti_0.47)O₃ (PSN-PB_xZT) ceramics with high Curie temperature and high piezoelectric properties were prepared by traditional solid state reaction measurement to meet the requirements for high temperature applications, and the crystal structure, dielectric, piezoelectric and ferroelectric properties were investigated. All the samples show a tetragonal crystal structure at room temperature and there was no noticeable change with the increasing of Ba²⁺ content. Doping of Ba²⁺ markedly improved piezoelectric properties of PSN-PZT, the maximum d₃₃~560 pC/N, T_c ~317 °C at x = 0.05. Their outstanding piezoelectric properties will drive the development of high temperature industrial applications.     

The decrease of depolarization temperature and the improvement of pyroelectric properties by doping Ta in lead-free 0.94Na0.5Bi0.5TiO3-0.06BaTiO3 ceramics

Ta-doped lead-free 0.94NBT-0.06BT-xTa (x=0.0–1.0%) ceramics were synthesized by a conventional solid-state route. XRD shows that the compositions are at a morphotropic phase boundary where rhombohedral and tetragonal phases coexist. The depolarization temperature (T_d) shifted to lower temperature with the increase of Ta content. The pyroelectric coefficient (p) of doped ceramics greatly enhanced compared with undoped material and reached a maximum of 7.14×10⁻⁴ C m⁻² °C⁻¹ at room temperature (RT) and 146.1×10⁻⁴ C m⁻² °C⁻¹ at T_d at x=0.2%. The figure of merits, F_i and F_v, also showed a great improvement from 1.12×10⁻¹⁰ m v⁻¹ and 0.021 m² C⁻¹ at x=0.0 to 2.55×10⁻¹⁰ m v⁻¹ and 0.033 m² C⁻¹ at x=0.2% at RT. Furthermore, F_i and F_v show the huge improvement to 52.2×10⁻¹⁰ m v⁻¹ and 0.48×10⁻¹⁰ m v⁻¹ respectively at T_d at x=0.2%. F_C shows a value between 2.26 and 2.42 ×10⁻⁹ C cm⁻² °C⁻¹ at RT at x=0.2%. The improved pyroelectric properties make NBT-0.06BT-0.002Ta ceramics a promising infrared detector material.     

Large electrostrain at high temperature in bismuth sodium titanate-based piezoelectric ceramics

(1-x)[0.82Bi_0.5Na_0.5TiO₃-0.18Bi_0.5K_0.5TiO₃]-xAgNbO₃ ceramics (abbreviated as BNKT-100xAN, x = 0–0.06) are fabricated by the solid state reaction method. It is discovered that silver niobate is completely dissolved into the lattice of 0.82Bi_0.5Na_0.5TiO₃-0.18Bi_0.5K_0.5TiO₃ ceramics based on characterization. The relaxation mechanism and characteristics of BNKT-100xAN ceramics are analyzed by dielectric temperature spectra and AC impedance spectra. The content of ordered domains and PNRs of BNKT-4AN ceramics is optimum, which enables it possess excellent electrostrain of 0.51%. The electrostrain almost remain constant after the 10⁴ cycles test, suggesting that it also has great fatigue resistance. After polarization at high temperature, large electrostrain of 1.4% and inverse piezoelectric constants of 2004 pm/V are obtained at 150 °C in BNKT-4AN ceramics. The ultrahigh electrostrain is mainly promoted by the larger polarizability of the <111>-oriented and <001>-oriented defect dipoles, the same direction of defect dipoles and the spontaneous polarization direction of phase, the pinning effects of the defect dipoles on the PNRs and the collinear arrangement of the PNRs. This work indicates that lead-free piezoelectric ceramics is hopeful to be applied in piezoelectrics working at high temperature. Simultaneously, a new design paradigm also is provided for the preparation of piezoelectric ceramics with excellent performance.     

Enhanced insulating and piezoelectric properties of BiFeO3-BaTiO3-Bi0.5Na0.5TiO3 ceramics with high Curie temperature

BiFeO₃-BaTiO₃ ceramics are promising lead-free piezoelectric ceramics due to their high piezoelectric properties and high Curie temperature, but their high leakage current density makes the poling difficult. In this study, a decreased leakage current density by three orders of magnitude was obtained in Bi_0.5Na_0.5TiO₃ (BNT) added 0.67BiFeO₃-0.33BaTiO₃ (BF-BT) ceramics. It was found that the largely improved insulating properties benefit from the reduced oxygen vacancies and weak reduction of Fe³⁺ to Fe²⁺ as confirmed by photoluminescence and X-ray photoelectron spectroscopy measurements, thereby contributing to high-temperature and high-field poling. In addition, the introduction of BNT leaded to increased grain size. Due to the grown grains as well as reduced oxygen vacancies and Fe²⁺, enhanced insulating and optimal piezoelectric properties with P_r = 24.2 µC/cm², d₃₃ = 183 pC/N, k_p = 0.28, and T_C = 467°C were achieved in BF-BT-0.05BNT ceramics.