A simple Bi3+ self-doping strategy constructing pseudo-tetragonal phase boundary to enhance electrical properties in CaBi2Nb2O9 high-temperature piezoceramics

Calcium bismuth niobate (CaBi₂Nb₂O₉, CBN)-based ceramics are promising candidates for high temperature application, the electrical properties of which are commonly enhanced by complex ion substitution or texture processes. Here, we report that high piezoelectricity and high resistivity were achieved in Ca_1-xBi_2+xNb₂O₉ by constructing pseudo-tetragonal boundary through a simple strategy of Bi³⁺ self-doping. At the pseudo-tetragonal boundary, Ca_0.96Bi_2.04Nb₂O₉ ceramics maintain high Curie temperature T_c = 942 °C, and show high piezoelectric coefficient d₃₃ = 15.1 pC/N and high resistivity ρ_dc = 2 × 10⁶ Ω cm (@600 °C). It is proved that the good piezoelectric property mainly originates from the increase of domain density. In addition, Ca_0.96Bi_2.04Nb₂O₉ ceramics reveal good thermal depoling performance, remaining 90% of piezoelectricity after thermal depoling at 900 ℃, which is due to small thermal expansion and structural distortion. Our work provides a promising candidate for high temperature applications and an easy way to improve the performance of Aurivillius-type piezoelectric ceramics.     

Tailoring structure and piezoelectric properties of CaBi2Nb2O9 ceramics by W6+-Doping

Calcium bismuth niobate (CaBi₂Nb₂O₉) is a typical bismuth-layer structured piezoelectrics (BLSPs) with a high Curie temperature (T_C) of ～943 °C, but it has low piezoelectric coefficient and high-temperature resistivity which severely limits signal acquisition in the high-temperature piezoelectric vibration sensors. Ion-doping modification is regarded as an effective way to enhance electrical properties. In this work, W⁶⁺ donor-doping at Nb⁵⁺ site in the CaBi₂Nb_2-xW_xO₉ (x = 0, 0.020, 0.025, 0.030, 0.035 and 0.040) piezoelectric ceramics with T_C of 931 ± 2 °C were fabricated by the conventional solid-state reaction method. The effects of W⁶⁺-doping on crystal structure of CaBi₂Nb_2-xW_xO₉ as well as microscopic morphology and electrical properties of ceramics were investigated systematically. The tetragonality, isotropy and electrical properties of the ceramics were enhanced with the introduction of W⁶⁺ dopant. It was found that x = 0.025 was the optimal W⁶⁺-doping ratio that yielded remnant polarization of 8.0 μC/cm², electrical resistivity of 3.0 × 10⁶ Ω cm at 600 °C, piezoelectric coefficient (d₃₃) of 14.4 pC/N, and good thermal depoling property. Our work has established a feasible approach to tune the structure of CaBi₂Nb₂O₉ to improve piezoelectric properties for potential applications in high-temperature piezoelectric vibration sensors.     

Ca2+ doping effects on the structural and electrical properties of Na0.5Bi4.5Ti4O15 piezoceramics

Bismuth layer structured Na_0.5Bi_4.5Ti₄O₁₅ (NBT) ferroelectric is one of the most promising materials for potential applications at high temperature. However, it is challenged to achieve a balance between high Curie temperature piezoelectric coefficient and excellent thermal stability for NBT piezoceramics. Here, through chemical modification at the A site of NBT with Ca²⁺, novel (Na_0.5Bi_0.5)_1-xCa_xBi₄Ti₄O₁₅ piezoceramics with excellent properties fabricated by solid state reaction were studied. After doping of Ca²⁺, the Curie temperature T_C increased from 648 °C to 662 °C while the piezoelectric coefficient d₃₃ increased from 14 pC/N to 22 pC/N which can be attributed to the intrinsic contribution of TiO₆ octahedral lattice distortion (tilting and rotation) and the extrinsic contribution of the increased density of domain walls. The composition of (Na_0.5Bi_0.5)_0.95Ca_0.05Bi₄Ti₄O₁₅ ceramics with x = 0.05 has the optimal performance with high T_C of 655 °C, large d₃₃ of 22 pC/N, high electrical resistivity ρ close to 10⁷ Ω cm at 500 °C and especially excellent thermal stability of d₃₃ only about 5% reduction after being annealed at 625 °C. The work effectively reveals the great potential of CNBT-5 ceramics for high-temperature piezoelectric applications.     

Significantly enhanced dc electrical resistivity and piezoelectric properties of Tb-modified CaBi2Nb2O9 ceramics for high-temperature piezoelectric applications

Bismuth layer–structured ferroelectric calcium bismuth niobate (CaBi₂Nb₂O₉, CBN) is considered to be one of the most potential high-temperature piezoelectric materials due to its high Curie temperature T_c of ∼940°C, but the drawbacks of low electrical resistivity at elevated temperature and low piezoelectric performance limit its applications as key electronic components at high temperature (HT). Herein, we report significantly enhanced dc electrical resistivity and piezoelectric properties of CBN ceramics through rare-earth element Tb ions compositional adjustment. The nominal compositions of Ca_1−xTb_xBi₂Nb₂O₉ (abbreviated as CBN-100xTb) have been fabricated by conventional solid-state reaction method. The composition of CBN-3Tb exhibits a significantly enhanced dc electrical resistivity of 1.97 × 10⁶ Ω cm at 600°C, which is larger by two orders of magnitude compared with unmodified CBN. The donor substitutions of Tb³⁺ ions for Ca²⁺ ions reduce the oxygen vacancy concentrations and increase the band-gap energy, which is responsible for the enhancement of dc electric resistivity. The temperature-dependent dc conduction properties reveal that the conduction is dominated by the thermally activated oxygen vacancies in the low-temperature region (200–350°C) and by the intrinsic conduction in the HT region (350–650°C). The CBN-3Tb also exhibits enhanced piezoelectric properties with a high piezoelectric coefficient d₃₃ of ∼13.2 pC/N and a high T_c of ∼966°C. Moreover, the CBN-3Tb exhibits good thermal stabilities of piezoelectric properties, remaining 97% of its room temperature value after annealing at 900°C. These properties demonstrate the great potentials of Tb-modified CBN for high-temperature piezoelectric applications.     

Phase transition and electrical properties of Bi0.5(Na0.8K0.2)0.5ZrO3 modified (K0.52Na0.48)(Nb0.95Sb0.05)O3 lead-free piezoelectric ceramics

In this work, (1−x)(K_0.52Na_0.48)Nb_0.95Sb_0.05O₃−xBi_0.5(Na_0.8K_0.2)_0.5ZrO₃ [abbreviated as (1−x)KNNS−xBNKZ, x=0–0.06] lead-free ceramics were fabricated using solid-state reaction method. The effects of BNKZ contents on the phase structure, piezoelectric and ferroelectric properties were investigated. The phase boundaries including orthorhombic-tetragonal (O-T) and rhombohedral-tetragonal (R-T) multiphase coexistence were identified by XRD patterns and temperature-dependent dielectric constant by adding different content of BNKZ. A giant field induced strain (~0.25%) along with converse piezoelectric coefficient d₃₃^* (~629.4 pm/V) and enhanced ferroelectricity P_r (~38 μC/cm²) were obtained when x=0.02, while the specimen with x=0.03 presented the optimal piezoelectric coefficient d₃₃ of 215 pC/N, due to the O-T or R-T phase coexistence near room temperature respectively. These results show that the introduction of Bi_0.5(Na_0.8K_0.2)_0.5ZrO₃ is a very effective way to improve the electrical properties of (K_0.52Na_0.48)(Nb_0.95Sb_0.05)O₃ lead-free piezoelectric ceramics.     

Crystal structure and electrical properties of (Li,Ce, Nd)-multidoped CaBi2Nb2O9 high temperature ceramics

(Li, Ce, and Nd)-multidoped CaBi₂Nb₂O₉ (CBN) Aurivillius phase ceramics were prepared via a conventional solid-state sintering route. The crystal structure including bond lengths and bond angles, microstructure, dielectric constant, DC resistivity, and piezoelectric properties were systematically investigated. Rietveld-refinements of X-ray results indicated that small quantity of (Li, Ce, Nd) doping (< 2.5 mol%) increases orthorhombic distortion, because of the smaller ionic radii of doping ions. However, orthorhombic distortion obviously decreased with increasing (Li, Ce, Nd) doping concentration from 5 to 25 mol%. The replacement of asymmetric A-site Bi³⁺ with 6s2 lone pair electrons by symmetric Li⁺, Ce³⁺ and Nd³⁺ ions decreased the orthorhombic distortion. The morphologies and electrical properties of sintered ceramics were tailored by the introducing (Li, Ce, Nd) multi-dopants. The improvement of piezoelectric properties of modified-CBN ceramics were attributed to decreasing grain sizes and morphotropic phase boundary (MPB). Ca_0.85(Li_0.5Ce_0.25Nd_0.25)_0.15Bi₂Nb₂O₉ (CBNLCN-15) ceramics had optimum properties, and d₃₃ and T_c values were found to be ~ 13.1 pC/N and ~ 900 °C, respectively.     

Enhanced electrical properties in W/Cu co-doped CaBi2Nb2O9 high-temperature piezoelectric ceramics

CaBi₂Nb₂O₉ (CBN)-based high-temperature piezoelectric ceramics with the formula of CaBi₂Nb_2−x(W_3/4Cu_1/4)_xO₉ were prepared via the traditional solid-state reaction method. Both the bulk microstructure and the electrical performance of the W/Cu co-doped CBN-based ceramics were systematically investigated. The results indicated that the W/Cu incorporation into the Nb-site altered the crystal structure, which enhanced the piezoelectricity and resistivity. The ceramic with the composition CaBi₂Nb_1.96(W_3/4Cu_1/4)_0.04O₉ exhibited good performance with a high d₃₃ (~14 pC/N) and T_C (~939℃). Moreover, the ceramic exhibited a good electrical resistivity (ρ) of 4.91 × 10⁵ Ω·cm and a low dielectric loss (tanδ) of 0.1 at 600℃. Furthermore, the ceramic that was annealed at 900℃ for 2 h presented a d₃₃ value of 13 pC/N, thus indicating good thermal stability of the piezoelectric properties. All these results confirm that the CaBi₂Nb_1.96(W_3/4Cu_1/4)_0.04O₉ ceramic may act as a potential promising candidate for piezoelectric device applications in high-temperature environments.     

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.     

Doping level effects in Nb self-doped Bi3TiNbO9 high-temperature piezoceramics with improved electrical properties

Nb self-doped Bi₃Ti_1-xNb_1+xO₉ (x = 0, 0.02, 0.04, 0.06, 0.08, and 0.1) high-temperature piezoelectric ceramics were fabricated through the conventional solid-state sintering method. The effects of different Nb self-doping levels on the microstructure, piezoelectric activities, and electrical conduction behaviors of these Nb self-doped Bi₃Ti_1-xNb_1+xO₉ ceramics were studied in detail. Large doping level effects on piezoelectric activity and resistivity were confirmed, which might be ascribed to the evolution of the crystal structure and the variations of the oxygen vacancy concentration and the grain anisotropy induced by Nb doping. An optimized piezoelectric coefficient (d₃₃) of 11.6 pC/N was achieved at x = 0.04 with a Curie temperature of 906°C. Additionally, an improved DC resistivity of 6.18 × 10⁵ Ω·cm at 600°C was acquired in this ceramic. Furthermore, the ceramic exhibited excellent thermal stability with the d₃₃ value maintaining 95% of its initial value after being annealed at 850°C for 2 hours. These results showed that Nb self-doped Bi₃Ti_1-xNb_1+xO₉ ceramics might have great potentials for high-temperature piezoelectric applications.     

Enhanced electrical properties related to structural distortion of CaBi2Nb2O9-based piezoelectric ceramics

CaBi₂Nb₂O₉ (CBN)-based high Curie temperature piezoelectric ceramics with formula Ca_0.8-xSr_x(Li_0.5Ce_0.15Bi_0.35)_0.2Bi₂Nb_1.94Ta_0.04W_0.02O₉ were prepared by conventional solid-state reaction method. The effects of strontium substitution for calcium in CBN pseudo-perovskite structure A-site were systematically studied. Results showed that the addition of Sr²⁺ ions lead to an improvement of the tetragonality of lattice structure, which resulted in an enhancement of piezoelectric and ferroelectric properties together with high Curie temperature T_C and good resistance to thermal depolarization. The analysis of dielectric spectrums revealed that the space charge polarization induced an additional dielectric anomaly occurred below T_C. The composition with x = 0.025 showed good integrated performance, the piezoelectric coefficient d₃₃ and T_C were ~17.5 pC/N and ~917°C, respectively. Even though the as-studied ceramics underwent high depolarizing temperature reached up to 875°C, d₃₃ decreased by 8% merely. The remanent polarization 2P_r and the resistivity ρ at 650°C were on the order of ~10 μC/cm² and 3 × 10⁵ Ω cm, respectively.     

High energy storage density and discharging efficiency in La3+/Nb5+-co-substituted (Bi0.5Na0.5)0.94Ba0.06TiO3 ceramics

In this work, [(Bi_1-xLa_x)_0.5Na_0.5]_0.94Ba_0.06(Ti_1-5y/4Nb_y)O₃ ceramics have been developed by the dual-substitution of La³⁺ for Bi³⁺ and Nb⁵⁺ for Ti⁴⁺ and prepared by an ordinary sintering technique. All ceramics can be well-sintered at 1200 °C. The addition of La³⁺ and Nb⁵⁺ reduces the grain size and improve the dielectric breakdown strength of the ceramics; moreover, after the introduction of La³⁺ and Nb⁵⁺, the remanent polarization of the ceramics is significantly reduced, while the maximum polarization remains the same large value as that of the ceramic without the doping of La³⁺ and Nb⁵⁺. As a result, high energy storage density and discharge efficiency are achieved at x/y = 0.07/0.02, giving the large storage density of 1.83 J/cm³ and high discharging efficiency of 70%. The present work presents a feasible strategy to develop energy storage materials based on perovskite ferroelectrics by the partial substitutions in the A and B sites.     

The structure and electrical properties of Ca0.6(Li0.5Bi0.5-xPrx)0.4Bi2Nb2O9 high-temperature piezoelectric ceramics

Ca_0.6(Li_0.5Bi_0.5-xPr_x)_0.4Bi₂Nb₂O₉ ceramics were prepared via a solid-state reaction method. The effect of the Pr content on the structural and electrical properties was systematically investigated. X-ray diffraction (XRD) combined with Rietveld refinement and X-ray photoelectron spectroscopy (XPS) demonstrated that a moderate amount of Pr³⁺ can be incorporated into the NbO₆ octahedra, while excess Pr³⁺ ions probably enter into the (Bi₂O₂)²⁺ layers, thus resulting in an increase in the tetragonality of the crystal structure. The introduction of Pr suppressed the generation of oxygen vacancies and improved the preferential grain growth along the c-axis, which might be responsible for enhancing the resistivity (ρ ~ 10⁶ Ω cm at 600°C). The replacement of Pr³⁺ for A-site Bi³⁺ enhanced the piezoelectric property, and the piezoelectric constant d₃₃ increased from 13.8 pC/N to 16.3 pC/N. The high depolarization temperature (up to 900°C) implied that CBN-LBP100x ceramics are promising candidates for ultrahigh-temperature application.     

Microstructural,structural and electrical properties of La3+-modified Bi4Ti3O12 ferroelectric ceramics

Bi_4?xLa_xTi₃O₁₂ (BLT) ceramics were prepared and studied in this work in terms of La³⁺-modified microstructure and phase development as well as electrical response. According to the results processed from X-ray diffraction and electrical measurements, the solubility limit (x_L) of La³⁺ into the Bi₄Ti₃O₁₂ (BIT) matrix was here found to locate slightly above x = 1.5. Further, La³⁺ had the effect of reducing the material grain size, while changing its morphology from the plate-like form, typical of BIT ceramics, to a spherical-like one. The electrical results presented and discussed here also include the behavior of the temperature of the ferroelectric–paraelectric phase transition as well as the normal or diffuse and/or relaxor nature of this transition depending on the La³⁺ content.     

Influence of Co/W co-doping on structural and electrical properties of Na0.5Bi2.5Nb2O9 piezoelectric ceramics

Co/W co-doped Na_0.5Bi_2.5Nb_2-x(Co_1/3W_2/3)_xO₉ (NBNCW-x) ceramic samples were prepared by the conventional solid state reaction method. The electrical properties and crystal structure of the NBNCW-x ceramic samples were analyzed in detail. The XRD and Rietveld refinement results showed that the samples lattice distortion decreased with the increment of Co/W doping. The XPS results showed that the number of oxygen vacancies in the Na_0.5Bi_2.5Nb₂O₉ ceramics could be reduced by the substitution of a small amount of Co/W. The weakened lattice distortion and reduced number of oxygen vacancies of the Na_0.5Bi_2.5Nb₂O₉ ceramics synergistically contributed to its improved electrical properties. In particular, the Na_0.5Bi_2.5Nb_1.97(Co_1/3W_2/3)_0.03O₉ ceramic exhibited the best performance, and its T_c, d₃₃ and P_r were 780 °C, 24.9 pC/N and 12.6 μC/cm², respectively. The dielectric loss was only 3.3% at 550 °C. In addition, this ceramic exhibited excellent thermal stability, with the d₃₃ value of the ceramic being 95.2% of its original value when annealed at 750 °C. These properties indicate that the Co/W co-doped Na_0.5Bi_2.5Nb₂O₉-based ceramics have potential application in the high-temperature field.     

Large piezoelectric coefficient with enhanced thermal stability in Nb5+-doped Ba0.85Ca0.15Zr0.1Ti0.9O3 ceramics

Chemical doping is an indispensable tool to tailor the properties of the commercial piezoelectric materials. However, a high piezoelectric coefficient with enhanced thermal stability is rarely achieved by one dopant in some high-performance ferroelectrics, e.g., the recently discovered eco-friendly (Ba_0.85Ca_0.15)(Zr_0.1Ti_0.9)O₃ (BCZT) ceramics. In order to optimize the piezoelectric property in BCZT system by a simple way, we investigated the doping effect of Fe³⁺, Nb⁵⁺ and Bi³⁺ cations in BCZT ceramics respectively. The results indicate that only Nb⁵⁺-doped BCZT ceramics display a combination of large piezoelectric coefficient and enhanced thermal stability, compared with others. Moreover, the established phase diagrams and in-situ transmission electron microscope (TEM) observations reveal that such optimized piezoelectric properties after Nb⁵⁺ doping originates from (i) the low polarization anisotropy near the ambient tetragonal (T)-orthorhombic (O) phase transition and (ii) the easy domain wall motion of persistent miniaturized ferroelectric domains upon heating.     

Dielectric temperature stability of Nb-modified Bi0.5(Na0.78K0.22)0.5TiO3 lead-free ceramics

In this study, the phase structure, microstructure and dielectric properties of Bi_0.5(Na_0.78K_0.22)_0.5(Ti_1-xNb_x)O₃ lead-free ceramics prepared by traditional solid phase sintering method were studied. The second phase pyrochlore bismuth titanate (Bi₂Ti₂O₇) was produced in the system after introduction of Nb⁵⁺. The dielectric constant of the sample (x = 0.03) sintered at 1130 °C at room temperature reached a maximum of 1841, and the dielectric loss was 0.045 minimum. It had been found that the K⁺ and Nb⁵⁺ co-doped Bi_0.5Na_0.5TiO₃ (BNT) lead-free ceramics exhibited outstanding dielectric-temperature stability within 100–400 °C with T_cc ≤±15%. Result of this research provides a valuable reference for application of BNT based capacitors in high temperature field.     

Large enhancement of piezoelectric properties and resistivity in Cu/Ta co-doped Bi4Ti3O12 high-temperature piezoceramics

In this study, the electrical properties of Bi₄Ti₃O₁₂-based Aurivillius-type ceramics were tailored by a B-site co-doping strategy combining high valence Ta⁵⁺ and low valence Cu²⁺. A series of Bi₄Ti_3−x(Cu_1/3Ta_2/3)_xO₁₂ (BTCT) (x = 0, 0.005, 0.01, 0.015, 0.02, 0.025, and 0.03) ceramics were prepared by the conventional solid-state reaction method. The effect of Cu/Ta co-doping on the crystal structure, microstructure, dielectric properties, piezoelectric properties, ferroelectric properties, and electrical conductivity of these ceramics was systematically investigated. Co-doping significantly enhanced the piezoelectric properties and DC electrical resistivity of the resulting composites. The optimized comprehensive performances were obtained at x = 0.015 with a large piezoelectric coefficient (34 pC/N) and a relatively high resistivity of 9.02 × 10⁶ Ω cm at 500°C. Furthermore, the ceramic also exhibited stable thermal annealing behaviors and excellent fatigue resistance. The results of this study demonstrated great potential of the Cu/Ta co-doped Bi₄Ti₃O₁₂ ceramics for high-temperature piezoelectric device applications.     

Enhanced energy storage performance in Na(1-3x)BixNb0.85Ta0.15O3 relaxor ferroelectric ceramics

High-performance lead-free dielectric containers have excellent energy storage performance such as higher power density and energy density. While being eco-friendly materials, lead-free dielectric materials are more suitable for pulse power systems than other dielectric materials. In this study, Ta⁵⁺and Bi³⁺ ions were introduced into the A site and B site of the NaNbO₃ matrix. The introduction of Bi³⁺ ions induced the formation of a vacancy in the A site, yielding Na_(1-3x)Bi_xNb_0.85Ta_0.15O₃ (NBNT, x = 0.05, 0.08, 0.11, 0.14) ceramics. The recoverable energy density (W_rec) and the energy storage efficiency (η) were highest for the Na_0.67Bi_0.11Nb_0.85Ta_0.15O₃ ceramic, with values of 3.37 J/cm³ and 89% respectively. Batteries employing the Na_0.67Bi_0.11Nb_0.85Ta_0.15O₃ ceramic achieved a current density of 830.4 A/cm², an energy density of 49.8 MW/cm³ and 60.2 ns discharge time. These results show that the Na_0.67Bi_0.11Nb_0.85Ta_0.15O₃ ceramic is an effective energy storage material with broad application prospects.     

Structure and electrical properties of Ca2+-doped (Na0.47Bi0.47Ba0.06)TiO3 lead-free piezoelectric ceramics

The lead-free piezoelectric ceramics (Na_.47Bi_.47Ba_.06)_1-xCa_xTiO₃ (x?=?0, 0.01, 0.02, 0.03, 0.05, and 0.08, abbreviated as BNBTC/0, BNBTC/1, BNBTC/2, BNBTC/3, BNBTC/5, and BNBTC/8, respectively) were obtained using the solid-state reaction method. The structure, electric conductivity, and dielectric, ferroelectric, and piezoelectric properties of the Ca²⁺-doped (Na_.47Bi_.47Ba_.06)TiO₃ ceramics were thoroughly investigated. The ceramics sintered at 1200?°C exhibit dense microstructures, having relative densities higher than 96%. The X-ray diffraction results demonstrate that all ceramics have a pure perovskite structure. The mean grain sizes of the ceramics are related to the Ca²⁺ quantity. A small quantity of Ca²⁺ ions (x?≤?0.03) improves the piezoelectric and ferroelectric properties of the samples. The dielectric behavior of the samples is sensitive to the Ca²⁺ content and electric poling. The results demonstrate that the electrical properties of the (Na_.47Bi_.47Ba_.06)TiO₃ lead-free ceramics can be well tuned by varying the Ca²⁺ quantity.     

The effect of B site doping of Nb5+ and aging process on the properties of BNKT-BT lead-free piezoelectric ceramics

This research explored the influence of Nb⁵⁺ doping on the electrical properties and microstructure of [0.852(Bi_0.5Na_0.5)-0.11(Bi_0.5K_0.5)-0.038Ba]Ti_(1-x)Nb_xO₃ (designated as BNKT-BT). The BNKT-BT samples were fabricated and the XRD results showed that the doping of Nb⁵⁺ ions induced a transformation from the coexistence of both rhombohedral and tetragonal phase to a single pseudo cubic phase. Also, the doping of Nb⁵⁺ ions caused the temperature of ferroelectric state-ergodic relaxor state transition to decrease below the room temperature (RT). The SEM observations showed that the Nb⁵⁺ doping had a minor effect on the grain size of BNKT-BT samples. In addition, the samples achieved a large electrostrain of 0.43% (d*₃₃ = S_max/E_max = 614 pm/V) under 7 kV/mm at RT. Moreover, the aging process employed at 80 °C for two weeks in air could effectively increase the electrostrain from 0.38% to 0.41% under 6 kV/mm (d*₃₃ = 683 pm/V) and reduce the strain hysteresis from 57% to 34%. These results indicated that the B site doping, combined with the aging process, could provide an effective way to enhance the electrostrain performance of lead-free piezoelectric ceramics.