Effects of BiMO3 on dielectric,ferroelectric, and piezoelectric properties of perovskite lead‐free piezoelectric BaTiO3–(Bi0.5Na0.5)TiO3 ceramics

New lead‐free piezoelectric ceramics of 0.9BaTiO₃–(0.1?x)(Bi_0.5Na_0.5)TiO₃–xBiMO₃, M=Al and Ga, where x=0.00‐0.10, were fabricated by the solid‐state reaction technique. The effect of BiMO₃ contents on the perovskite structure, phase transition, and dielectric, ferroelectric, and piezoelectric properties was investigated. X‐ray diffraction patterns showed that the ceramics exhibit a monophasic perovskite phase up to x=0.06, suggesting stabilized perovskite structures with B‐site aliovalent substitutions. Compositional‐dependent phase transitions were observed from tetragonal to pseudo‐cubic phase with increasing BiMO₃ amounts. Al³⁺ ions were found to stabilize the transition temperature of the ceramics, while significantly decreasing transition temperature, and a change in the dielectric peak were found with an increasing amount of Ga³⁺. Regarding Al³⁺ substitution, the remanent polarization (P_r) values were found to decrease slightly with the Al³⁺ amount. With regard to Ga³⁺ substitution, P_r values decreased with the Ga³⁺ amount up to 0.06 and then increased slightly. The ceramics became softer with a higher degree of substitution according to the lower coercive field (E_c), when compared with 0.9BaTiO₃–0.1(Bi_0.5Na_0.5)TiO₃ ceramics. Ceramics with a lower degree of substitution and tetragonal phase showed butterfly strain loops that correlated with normal ferroelectric behavior.     

Photoluminescence and Temperature Dependent Electrical Properties of Er‐Doped 0.94Bi0.5Na0.5TiO3‐0.06BaTiO3 Ceramics

Er‐doped 0.94Bi_0.5Na_0.5TiO₃‐0.06BaTiO₃ (BNT‐6BT: xEr, x is the molar ratio of Er³⁺ doping) lead‐free piezoceramics with x = 0–0.02 were prepared and their multifunctional properties have been comprehensively investigated. Our results show that Er‐doping has significant effects on morphology of grain, photoluminescence, dielectric, and ferroelectric properties of the ceramics. At room temperature, the green (550 nm) and red (670 nm) emissions are enhanced by Er‐doping, reaching the strongest emission intensity when x = 0.0075. The complex and composition‐dependent effects of electric poling on photoluminescence also have been measured. As for electrical properties, on the one hand, Er‐doping tends to flatten the dielectric constant‐temperature (ε_r‐T) curves, leading to temperature‐insensitive dielectric constant in a wide temperature range (50°C–300°C). On the other hand, Er‐doping significantly decreases the ferroelectric‐relaxor transition temperature (T_F–R) and depolarization temperature (T_d), with the T_F–R decreasing from 76°C to 42°C for x = 0–0.02. As a result, significant composition‐dependent electrical features were found in ferroelectric and piezoelectric properties at room temperature. In general, piezoelectric and ferroelectric properties tend to become weaker, as confirmed by the composition‐dependent piezoelectric coefficient (d₃₃), planar coupling factor (k_p), and the shape of polarization‐electric field (P–E), current‐electric field (J–E), bipolar/unipolar strain‐electric field (S–E) curves. Furthermore, to understand the relationship between the T_F–R/T_d and the electrical properties, the composition of x = 0.0075 has been intensively studied. Our results indicate that the BNT‐6BT: xEr with appropriate Er‐doping may be a promising multifunctional material with integrated photoluminescence and electrical properties for practical applications.     

Remarkable piezoelectricity and stable high‐temperature dielectric properties of quenched BiFeO3–BaTiO3 ceramics

Effects of quenching process on dielectric, ferroelectric, and piezoelectric properties of 0.71BiFeO₃?0.29BaTiO₃ ceramics with Mn modification (BF–BT?xmol%Mn) were investigated. The dielectric, ferroelectric, and piezoelectric properties of BF–BT?xmol%Mn were improved by quenching, especially to the BF–BT?0.3 mol%Mn ceramics. The dielectric loss tanδ of quenched BF–BT?0.3 mol%Mn ceramics was only 0.28 at 500°C, which was half of the slow cooling one. Meanwhile, the remnant polarization P_r of quenched BF–BT?0.3 mol%Mn ceramics increased to 21 μC/cm². It was notable that the piezoelectric constant d₃₃ of quenched BF–BT?0.3 mol%Mn ceramics reached up to 191 pC/N, while the T_C was 530°C, showing excellent compatible properties. The BF–BT?xmol%Mn system ceramics showed to obey the Rayleigh law within suitable field regions. The Rayleigh law results indicated that the extrinsic contributions to the dielectric and piezoelectric responses of quenched BF–BT?xmol%Mn ceramics were larger than the unquenched ceramics. These results presented that the quenched BF–BT?xmol%Mn ceramics were promising candidates for high‐temperature piezoelectric devices.     

Temperature‐Dependent Phase Transitions in the Lead‐Free Piezoceramics (1 – x – y)(Bi1/2Na1/2)TiO3–xBaTiO3–y(K0.5Na0.5)NbO3 Observed by in situ Transmission Electron Microscopy and Dielectric Measurements

Lead‐free piezoelectric (1 – x – y)(Bi_1/2Na_1/2)TiO₃–xBaTiO₃–y(K_0.5Na_0.5)NbO₃ (BNT–BT–KNN) ceramics were examined in situ under increasing temperature in the transmission electron microscope. Changing superstructure reflections indicate a transition from rhombohedral to tetragonal to cubic phase with broad coexistence regions. The additional evolution of the microstructure in combination with dielectric measurements leads to a model of two relaxor‐type phase evolutions with temperature.     

Effect of Texture on Temperature‐Dependent Properties of K0.5Na0.5NbO3 Modified Bi1/2Na1/2TiO3–xBaTiO3

Textured (1?x?y)Bi_1/2Na_1/2TiO₃–xBaTiO₃–yK_0.5Na_0.5NbO₃ (BNT–100xBT–100yKNN) ceramics with a {001} pseudocubic (pc) orientation were fabricated by templated grain growth using Bi_1/2Na_1/2TiO₃ templates. Temperature‐dependent electromechanical results demonstrate that the strain response of templated BNT–xBT–yKNN ceramics is stable from room temperature (RT) to 125°C. The temperature‐dependent strain and polarization response are compared to randomly oriented ceramics, for BNT–100xBT–2KNN (0.05 ≤ x ≤ 0.07). Textured BNT–7BT–2KNN reached a maximum 0.47% strain response at 5 kV/mm, an almost 50% increase compared to randomly oriented BNT–7BT–2KNN. Over the temperature range RT–125°C, the strain response of templated BNT–6BT–2KNN degraded from 0.38% to 0.22% (?42.1%) compared to 0.37% to 0.18% (?51.4%) for randomly oriented ceramics. The temperature‐dependent strain response suggests that templated BNT–100xBT–100yKNN ceramics are well suited for elevated temperature applications.     

Structure,Ferroelectric, Piezoelectric,and Ferromagnetic Properties of BiFeO3‐BaTiO3‐Bi0.5Na0.5TiO3 Lead‐Free Multiferroic Ceramics

Lead‐free multiferroic ceramics of BiFeO₃‐BaTiO₃‐Bi_0.5Na_0.5TiO₃ have been prepared by a conventional ceramic technique. The microstructure, multiferroic, and piezoelectric properties of the ceramics have been studied. The ceramics sintered at 1000°C for 2 h possess a pure perovskite structure and a morphotropic phase boundary of rhombohedral and tetragonal phases is formed at x = 0.02. After the addition of Bi_0.5Na_0.5TiO₃, two dielectric anomalies are observed at high temperatures (T_m ~ 510°C–570°C and T₂ ~ 720°C). The phase transition around T_m becomes wider gradually with increasing x. The ferroelectricity, piezoelectricity, and ferromagnetism of the ceramics are significantly improved after the addition of Bi_0.5Na_0.5TiO₃. High resistivity (~1.3 × 10⁹ Ω·cm), strong ferroelectricity (P_r = 27.4 μC/cm²), good piezoelectricity (d₃₃ =140 pC/N, k_p = 31.4%), and weak magnetic properties (M_r =0.19 emu/g) are observed.     

Peculiar dielectric properties of (1-x)(K,Na)(Nb,Sb)O3−x(Bi,Na)ZrO3 ceramics

In spite of the significance from both scientific and technological viewpoints, systematical studies on the dielectric spectra of (K,Na)NbO₃-based lead-free ceramics particularly in the poled state had been scarcely performed so far. In this study, the compositional series of (1-x)(K_0.48Na_0.52)(Nb_0.96Sb_0.04)O₃?x(Bi_0.50Na_0.50)ZrO₃ ceramics were chosen representatively to shed more light on the characters of dielectric properties. All the ceramics in the unpoled state show dielectric spectra of large dispersion with the relaxational characteristic frequency higher than the measured upper limit of 60 MHz at room temperature. Additional resonance peaks due to the electromechanical coupling of piezoelectric effect appear and are accompanied by a large step-like reduction of dielectric permittivity ε′ in the dielectric spectra after poling. An abnormal phenomenon that poling induces the increase of low-frequency ε′ occurs in those ceramics with x ≥ 0.04 at room temperature, and is confirmed to associate closely with the orthorhombic-tetragonal and rhombohedral-orthorhombic polymorphic phase transitions. Further study of domain structure indicates that the origin of this abnormal phenomenon should be ascribed to the enhancement of domain-wall mobility because of the large reduction of domain-wall density due to the poling.     

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.     

Giant electromechanical strain response in lead‐free SrTiO3‐doped (Bi0.5Na0.5TiO3–BaTiO3)–LiNbO3 piezoelectric ceramics

Lead‐free 0.985[(0.94?x)Bi_0.5Na_0.5TiO₃–0.06BaTiO₃–xSrTiO₃]–0.015LiNbO₃ [(BNT–BT–xST)–LN, x=0‐0.05] piezoelectric ceramics were prepared using a conventional solid‐state reaction method. It was found that the long‐range ferroelectric order in the unmodified (BNT–BT)–LN ceramic was disrupted and transformed into the ergodic relaxor phase with the ST substitution, which was well demonstrated by the dramatic decrease in remnant polarization (P_r), coercive field (E_c), negative strain (S_neg) and piezoelectric coefficient (d₃₃). However, the degradation of the ferroelectric and piezoelectric properties was accompanied by a significant increase in the usable strain response. The critical composition (BNT–BT–0.03ST)–LN exhibited a maximum unipolar strain of ~0.44% and corresponding normalized strain, S_max/E_max of ~880 pm/V under a moderate field of 50 kV/cm at room temperature. This giant strain was associated with the coexistence of the ferroelectric and ergodic relaxor phases, which should be mainly attributed to the reversible electric‐field‐induced transition between the ergodic relaxor and ferroelectric phases. Furthermore, the large field‐induced strain showed relatively good temperature stability; the S_max/E_max was as high as ~490 pm/V even at 120°C. These findings indicated that the (BNT–BT–xST)–LN system would be a suitable environmental‐friendly candidate for actuator applications.     

Dielectric,Ferroelectric, and Piezoelectric Properties of BiFeO3–BaTiO3 Ceramics

Perovskite solid solution ceramics of (1 ? x)BiFeO₃–xBaTiO₃ (1 ? x)BF–xBT, 0.2 ≤ x ≤ 0.45) with high electrical resistivity were prepared by solid‐state reaction method. Actual ferroelectric hysteresis loops and temperature dependence of dielectric constant of the ceramics were obtained. Ceramics of 0.7BF–0.3BT with small rhombohedral distortion show highest remnant polarization (P_r = 26.0 μC/cm²) and piezoelectric coefficient (d₃₃ = 134 pC/N). Compositions with pseudo‐cubic symmetry (intermediate phases) show relaxor‐like dielectric anomaly. The values of P_r and d₃₃ decrease with increasing BT content, from 24.8 μC/cm² and 104 pC/N for 0.65BF–0.35BT to 8.2 μC/cm² and 5 pC/N for 0.55BF–0.45BT.     

Effects of Bi0.5Na0.5HfO3 addition on the phase structure and piezoelectric properties of (K,Na)NbO3‐based ceramics

Lead‐free perovskite (1‐x)(K_0.48Na_0.48Li_0.04)Nb_0.95Sb_0.05O₃‐x(Bi_0.5Na_0.5)HfO₃ piezoelectric ceramics were prepared by a traditional ceramic fabrication method. An investigation was conducted to assess the effects of (Bi_0.5Na_0.5)HfO₃ content on the crystal structure, microstructure, phase‐transition temperatures, and piezoelectric properties of the ceramics. The X‐ray diffraction results, combined with the temperature dependence of dielectric properties, revealed that the ceramics experienced a structural transition from an orthorhombic phase to a tetragonal phase with the addition of (Bi_0.5Na_0.5)HfO₃, and a coexistence of orthorhombic and tetragonal phases was identified in the composition range of 0.005≤x≤0.015. An obviously improved piezoelectric activity was obtained for the ceramics with compositions near the orthorhombic‐tetragonal phase boundary, among which the composition x=0.005 exhibited the maximum values of piezoelectric constant d₃₃, and planar and thickness electromechanical coupling coefficients (k_p and k_t) of 246 pC/N, 0.435, and 0.554, respectively. Furthermore, the Curie temperature of the ceramics was found decreasing with the increase in (Bi_0.5Na_0.5)HfO₃ content, but still maintaining above 300°C for the phase boundary compositions. These results indicate that the ceramics are promising lead‐free candidate materials for piezoelectric applications.     

The Relationship Between Phase Structure and Electrical Properties in (1 − x)(Bi0.5Na0.5TiO3–Ba0.5K0.5TiO3–BaTiO3)‐ xK0.5Na0.5NbO3 Quaternary Lead‐Free Piezoelectric Ceramics

(1 ? x)(0.85Bi_0.5Na_0.5TiO₃–0.11Ba_0.5K_0.5TiO₃–0.04BaTiO₃)‐ xK_0.5Na_0.5NbO₃ lead‐free piezoelectric ceramics with x = 0.00, 0.02, 0.03, 0.04, 0.05, and 0.10 were prepared by a conventional solid state method. A coexistence of rhombohedral (R) and tetragonal (T) phases was found in the system, which tended to evolve into pseudocubic symmetry when x increases. The x = 0.04 sample exhibited improved electrical properties: the dielectric constant ε_r = 1900 with the low loss tangents 0.06, the S_max/E_max of ~400 and ~460 pm/V under unipolar and bipolar electric field, respectively. Meanwhile, piezoelectric constant d₃₃ still maintained ~160 pC/N. These could be owed to the formation of polar nanoregions for relaxor phase.     

Low‐Temperature Sintering of Bi0.5(Na,K)0.5TiO3 for Multilayer Ceramic Actuators

We investigated the influence of CuO amount (0.5–3.0 mol%), sintering temperature (900°C–1000°C), and sintering time (2–6 h) on the low‐temperature sintering behavior of CuO‐added Bi_0.5(Na_0.78K_0.22)_0.5TiO₃ (BNKT22) ceramics. Normalized strain (S_max/E_max), piezoelectric coefficient (d₃₃), and remanent polarization (P_r) of 1.0 mol% CuO‐added BNKT22 ceramics sintered at 950°C for 4 h was 280 pm/V, 180 pC/N, and 28 μC/cm², respectively. These values are similar to those of pure BNKT22 ceramics sintered at 1150°C. In addition, we investigated the performance of multilayer ceramic actuators made from CuO‐added BNKT22 in acoustic sound speaker devices. A prototype sound speaker device showed similar output sound pressure levels as a Pb(Zr,Ti)O₃‐based device in the frequency range 0.66–20 kHz. This result highlights the feasibility of using low‐cost multilayer ceramic devices made of lead‐free BNKT‐based piezoelectric materials in sound speaker devices.     

Remarkably High‐Temperature Stability of Bi(Fe1−xAlx)O3–BaTiO3 Solid Solution with Near‐Zero Temperature Coefficient of Piezoelectric Properties

The 0.72Bi(Fe_1?xAl_x)O₃–0.28BaTiO₃ (x = 0, 0.01, 0.03, 0.05, and 0.07, abbreviated as BFAx–BT) lead‐free high‐temperature ceramics were prepared by the conventional ceramic processing. Systematic investigation on the microstructures, crystalline structures, dielectric and piezoelectric properties, and high‐temperature stability of piezoelectric properties was carried out. The crystalline structures of BFAx–BT ceramics evolve from rhombohedral structure with x < 0.01 to the coexistence of rhombohedral structure and pseudocubic phases with x ≈ 0.01, finally to pseudocubic phases when x > 0.03. Remarkably high‐temperature stability with near‐zero temperature coefficient of piezoelectric properties (TCk_p), together with improved piezoelectric properties has been achieved for x = 0.01 BFAx–BT ceramics. The BFAx–BT(x = 0.01) ceramics simultaneously show the excellent piezoelectric properties of d₃₃ = 151 pC/N, k_p = 0.31 and super‐high‐temperature stability of T_d = 420°C, TCk_p = 1 × 10^?4. It is considered that the observed strong piezoelectricity and remarkably high‐temperature stability should be ascribed to the phase coexistence of rhombohedral and pseudocubic phases. The rhombohedral phases have a positive TCk_p value and the pseudocubic phases possess a negative TCk_p value. Thus, the TCk_p value of BFAx–BT ceramics can be tuned by composition of x.     

Polar domain structural evolution under electric field and temperature in the (Bi0.5Na0.5)TiO3-0.06BaTiO3 piezoceramics

Lead-free bismuth sodium titanate and related compounds are of great interest as promising candidates for piezoelectric applications. However, the full understanding of this family of materials is still a challenge partly because of their structural complexity and different behaviors with or without the application of an external electric field. Here, piezoresponse force microscopy is used to gain insight into the mesoscopic-scale domain structure of the morphotropic phase boundary (MPB) composition of (1-x)Bi_0.5Na_0.5TiO₃-xBaTiO₃ solid solution at x = 0.06 (abbreviated as BNT-6BT). The evolution of the domains with the changes of the electric field and temperature has been thoroughly examined in conjunction with the crystal structure analysis and dielectric studies. It is found that ferroelectric domains with size of hundreds of nanometers are embedded in a relaxor state without visible domains on a mesoscopic scale, which are considered to contribute to the tetragonal and cubic phases in the material, respectively. Temperature-independent domain configuration is observed in the unpoled sample from room temperature to 200°C. While, temperature-dependent domain configuration is observed in the poled sample. The homogenously poled state breaks into the mixed domain configuration containing polydomain structure and invisible state around the so-called depoling temperature. The structural changes on different length scales are also discussed. This work provides an in-depth understanding of the structural and domain changes under an electric field and the temperature-dependent domain evolution in both unpoled and poled states in the BNT-BT solid solution of the MPB composition.     

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.     

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.     

Effects of K0.5Bi0.5TiO3 addition on dielectric properties of BaTiO3 ceramics

(1?x)BaTiO₃–xK_0.5Bi_0.5TiO₃ (abbreviated as BT–KBT, 0.10≦x≦0.15) dielectric ceramics were prepared by a conventional oxide mixing method. The effects of KBT content on the densification, microstructure and dielectric properties of BT ceramics were investigated. The density characterization results show that the addition of KBT significantly lowered the sintering temperature of BT ceramics to about 1280 °C. The XRD results showed that the phase compositions of all samples were pure tetragonal phases. The dielectric constant and dielectric loss firstly increased and then decreased with the increase of KBT. In addition, dielectric constant and dielectric loss versus frequency were characterized in the frequency range from 100 Hz to 2 MHz. It is found that the dielectric constant and the dielectric loss changed with the increase of KBT contents regularly.     

Enhanced microstructure and electrical properties of Mn-modified Bi0.5(Na0.65K0.35)0.5TiO3 ferroelectric ceramics

Bi_0.5(Na_0.65K_0.35)_0.5TiO₃ (BNKT) and Mn-modified Bi_0.5(Na_0.65K_0.35)_0.5(Mn_xTi_1−x)O₃ (BNKMT-10³x), (x=0.0–0.5%) ferroelectric ceramics were synthesized by solid-state reaction method. Optimization of calcination temperature in Mn-doped ceramics was carried out for the removal of secondary phases observed in XRD analysis. BNKMT ceramics sintered at 1090 °C showed enhanced dielectric, piezoelectric and ferroelectric properties in comparison to pure BNKT. The average grain size was found to increase from 0.35 μm in BNKT to 0.52 μm in Bi_0.5(Na_0.65K_0.35)_0.5(Mn_0.0025Ti_0.9975)O₃ (BNKMT-2.5) ceramics. The dielectric permittivity maximum temperature (T_m) was increased to a maximum of 345 °C with Mn-modification. AC conductivity analysis was performed as a function of temperature and frequency to investigate the conduction behavior and determine activation energies. Significant high value of piezoelectric charge coefficient (d₃₃=176 pC/N) was achieved in BNKMT 2.5 ceramics. Improved temperature stability of ferroelectric behavior was observed in the temperature dependent P–E hysteresis loops as a result of Mn-incorporation. The fatigue free nature along with enhanced dielectric and ferroelectric properties make BNKMT-2.5 ceramic a promising candidate for replacing lead based ceramics in device applications.     

Properties and structures of nonstoichiometric (K,Na)NbO3‐based lead‐free ceramics

The 0.968[(K_0.48Na_0.52)]Nb_0.95+xSb_0.05O₃–0.032(Bi_0.5Na_0.5)ZrO₃ [KNN_xS–BNZ] lead‐free ceramics with nonstoichiometric niobium ion were fabricated via conventional solid‐state sintering technique and their piezoelectric, dielectric and ferroelectric properties were investigated. When x = 0.010, enhanced piezoelectric properties (d₃₃ ≈ 421 pC/N and k_p ≈ 0.47) were obtained due to the construction of rhombohendral—tetragonal phase boundary near room temperature. The KNN_xS–BNZ ceramics possesses enhanced Curie temperature (T_c) with improved piezoelectric constant. A large d₃₃ of ~421 pC/N and a high T_c ~256°C can be simultaneously induced in the ceramics with x = 0.010. Especially, good thermal stability was observed in a broad temperature range. The results indicated that our work could benefit development of KNN‐based ceramics and widen their application range.