Enhanced electrical properties of the polymorphic phase boundary on the tetragonal side in K0.48Na0.52NbO3-based lead-free piezoelectric ceramics

Herein, (0.95?x)K_0.48Na_0.52NbO₃-0.05SrTiO₃-xCaZrO₃ piezoelectric ceramics were prepared using a conventional solid sintering process, and their microstructures, phase structures, and ferroelectric, dielectric, and strain properties were studied. The crystal structure of the ceramics changed from the coexistence of an orthogonal–tetragonal phase on the orthogonal side at x = 0 to that on the tetragonal side at x = 0.02 by improving the orthogonal–tetragonal transition temperature (～20 °C) with increasing CaZrO₃ (abbreviated as CZ) doping. A high electric field–induced strain of 0.33% with a Curie temperature of T_c = 256 °C was obtained at x = 0.02 and was approximately two times that observed at x = 0. The dielectric constant and maximum polarization were the highest at x = 0.02 in this (0.95?x)K_0.48Na_0.52NbO₃-0.05SrTiO₃-xCaZrO₃ system. These materials would be promising lead-free ceramics in the future.     

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.     

The electrical properties of (1−x)(Bi0.5Na0.5TiO3–Bi0.5K0.5TiO3–BaTiO3)–xCaZrO3 lead-free piezoelectric ceramics

Lead-free (1−x)(0.0852Bi_0.5Na_0.5TiO₃–0.12Bi_0.5K_0.5TiO₃–0.028BaTiO₃)–xCaZrO₃ piezoelectric ceramics (BNT−BKT−BT−xCZ, x=0, 0.01, 0.02, 0.03, 0.04 and 0.05) were prepared by using a conventional solid-state reaction method. The effects of CZ-doping on the structural, dielectric, ferroelectric and piezoelectric properties of the BNT−BKT−BT−xCZ system were systematically investigated. The polarization and strain behaviors indicated that the long-range ferroelectric order in the unmodified BNT−BKT−BT ceramics was disrupted by the increase of CZ-doping content, and correspondingly the depolarization temperature (T_d) shifted down from 109 °C to below room temperature. When x>0.03, accompanied with the drastic decrease in the remnant polarization (P_r) and piezoelectric coefficient (d₃₃), the electric-field-induced strain was enhanced significantly. A large unipolar strain of 0.35% under an applied electric field of 70 kV/cm (S_max/E_max=500 pm/V) was obtained in the BNT−BKT−BT−0.04CZ ceramics at room temperature, which was attributed to the reversible electric-field-induced phase transition between the relaxor and ferroelectric phases.     

The high nano-domain improves the piezoelectric properties of KNN lead-free piezo-ceramics

Due to their high Curie temperature and large dielectric constant, potassium sodium niobate-based lead-free piezo-ceramics (KNN) are regarded as one of the most hopeful piezo-ceramics candidate materials. Herein, (1-x) (K_0.5Na_0.5)(Nb_0.96Sb_0.04)O₃ - x (Ba_0.5Sr_0.25)ZrO₃ [abbreviated as (1-x) KNNS - x BSZ, x = 0, 0.01, 0.02, 0.03, 0.04 and 0.05] lead-free piezo-ceramics are prepared through chemical doping using the traditional solid phase method. The phase structure, domain structure, and microstructure of KNN ceramics have been thoroughly examined. Doping of BZS causes the formation of R-O-T phase boundaries and increases the proportion of polar nano-domains within the crystals, thus increasing the rate of motion of the domain walls and making the domains more easily deflected. The piezoelectric and dielectric properties of the material are improved simultaneously. When x = 0.04, the piezoelectric properties of ceramics reach the optimal value (d₃₃ = 351 pC/N, T_C = 305 °C, K_p = 43% and ε_r = 41267). This work offers a fresh concept for enhancing the overall performance of lead-free piezo-ceramics and aids in understanding the nature of doping modification of lead-free piezo-ceramics.     

Design on improving piezoelectric strain and temperature stability of KNN-based ceramics

Lead-free 0.99(0.96K_0.46Na_0.54Nb_1-xTa_xO₃-0.04Bi_0.5(Na_0.82K_0.18)_0.5ZrO₃)-0.01CaZrO₃ (0.99(0.96KNNTax-0.04BNZ)-0.01CZ) ceramics were prepared by a solid-state sintering method. Ta₂O₅ doped in the 0.99(0.96KNNTax-0.04BNZ)-0.01CZ ceramics results in a phase structure transition from the orthorhombic (O)/tetragonal (T) phase to the rhombohedral (R)/T phase. The Ta₂O₅ dopant induces a decrease in the average grain size from ~1.70 to ~0.69 μm. At x = 0.02 and 0.04, the ceramics have a high reverse piezoelectric coefficient (~500 pm/V under 25 kV/cm). The ceramics with x = 0.04 show an optimal level of unipolar strain, reaching 0.17% under 35 kV/cm at room temperature, and their field-induced strain varies <10% in the temperature range from 25 to 135°C. The presence of the O phase in the polymorphic phase boundary (PPB) improves the temperature stability the reverse piezoelectric coefficient (). Obtaining KNN-based ceramics with good piezoelectric properties and weak temperature sensitivity by designing a R/O/T phase boundary and controlling the average grain size to the submicrometer level is highly feasible.     

Giant strain response with low hysteresis in potassium sodium niobate based lead-free ceramics

In this work, the relationships between the composition-driven phase boundary, ferroelectricity and strain properties of the (1-x)(K_0.48Na_0.52)(Nb_1-ySb_y)O₃-xBi_0.5(Na_0.82K_0.18)_0.5ZrO₃ (abbreviated as (1-x)KNN_1-yS_y-xBNKZ) ceramics were investigated. A giant electric field-induced strain of 0.3% (d₃₃¹ = 750 p.m./V) and a low hysteresis (16.4%) were obtained in the 0.97KNN_0.98S_0.02-0.03BNKZ ceramics. The giant strain is attributed to the enhanced piezoelectricity induced by the appearance of the O-T phase boundary and the electric-field-induced phase transition from the relaxor phase to the ferroelectric phase. Furthermore, the 0.97KNN_0.98S_0.02-0.03BNKZ ceramics exhibit good thermal stability in the temperature range from 25 °C to 150 °C. Hence, this work can promote the practical applications of KNN-based lead-free piezoelectric ceramics in highly sensitive and precise piezoelectric actuators.     

Ferroelectric‒to‒relaxor crossover in KNN‒based lead‒free piezoceramics

This study investigated the phase transition behavior and electrical properties of (K_0.5Na_0.5)(Nb_1-xZr_x)O₃ (KNN?100xZ) and (K_0.5Na_0.5)NbO₃–yBaZrO₃ (KNN–100yBZ) lead–free piezoelectric ceramics. The phase transitions in crystal structures were compared in KNN ceramics between single Zr⁴⁺ doping and Ba²⁺Zr⁴⁺ co?doping. Piezoelectric properties such as the piezoelectric constant (d₃₃) and electromechanical coupling factor (k_p) are optimized for KNN?6BZ ceramics and were clarified via the polymorphic phase transition from the orthorhombic to pseudocubic phase. The fitted degree of diffuseness (γ) for a phase transition from the modified Curie–Weiss law indicated that KNN ceramics as ferroelectrics are gradually transformed through BaZrO₃ modification. Accordingly, the enhanced strain properties at y = 0.08 consist of coexisting ferroelectric domains and polar nanoregions that are supported by ferroelectric–to–relaxor crossover in KNN?100BZ ceramics.     

Coexistence of excellent piezoelectric performance and thermal stability in KNN-based lead-free piezoelectric ceramics

With close attention being paid to environmental issues and more legislation coming into force to limit the application of Pb-based materials, accelerating research on lead-free piezoelectric ceramics has become increasingly requisite and urgent. Herein, we have devised and synthesized (1-x)(K_0.5Na_0.5)_0.98Ag_0.02(Nb_0.96Sb_0.04)O₃-x(Bi_0.5Na_0.5)ZrO₃ [abbreviated as (1-x)KNANS-xBNZ, x = 0.01, 0.02, 0.03, 0.035, 0.04, 0.045, 0.05, 0.06] Pb-free ceramics. Phase transition, microstructure, electrical properties, and temperature stability of the ceramics have been comprehensively investigated. The findings illustrate that optimizing BNZ content can give rise to a rhombohedral-tetragonal (R-T) phase boundary when x = 0.04, 0.045, 0.05. The specimens with x = 0.04 show improved piezoelectric properties (d₃₃ ~ 440 pC/N, k_p ~ 53%, T_C ~ 250 °C, d₃₃* ~ 553 pm/V) and good temperature stability. The overall performance is excellent and indicates that (1-x)KNANS-xBNZ ceramics have great potential for replacing their lead-based counterparts.     

Chemical composition and tolerance factor at the morphotropic phase boundary in (Bi0.5Na0.5)TiO3-based piezoelectric ceramics

A quantitative relation between the morphotropic phase boundary (MPB) composition and the tolerance factor (t) in (Bi_0.5Na_0.5)TiO₃ (BNT)-based piezoelectric ceramics was established. The t value of the MPB compositions in BNT-based ceramics is around 0.990–0.993 and is independent of the types of added compounds. In order to experimentally demonstrate it, two piezoelectric ceramic systems (1 ? x)(Bi_0.5Na_0.5)TiO₃–x(Ba_1?aSr_a)TiO₃, a = 0.05 and 0.3 (BNBST5-x and BNBST30-x, x < 12%), were used. X-ray diffraction patterns and the lattice parameter investigations revealed that these two systems formed solid solutions within the studied stoichiometry and showed a rhombohedral–tetragonal phase transformation. Furthermore, both the structure analysis and electric properties measurements indicated that the MPB compositions were BNBST5-6 and BNBST30-8 and their corresponding t value were 0.9900 and 0.9903, respectively. The results confirm the relation between the MPB composition and t value and provide a method for designing new piezoelectric materials.     

Phase transition behavior and electrical properties of lead-free (1 − x)(0.98K0.5Na0.5NbO3–0.02LiTaO3)–x(0.96Bi0.5Na0.5TiO3–0.04BaTiO3) piezoelectric ceramics

Lead-free piezoelectric ceramics (1 − x)(0.98K_0.5Na_0.5NbO₃–0.02LiTaO₃)–x(0.96Bi_0.5Na_0.5TiO₃–0.04BaTiO₃) (KNN–LT–BNT–BT) with x = 0–0.10 have been synthesized by a conventional sintering technique. All samples possess pure perovskite structure, showing room temperature symmetries of orthorhombic at x < 0.02, and tetragonal at 0.05 ≤ x ≤ 0.10. A coexistence of orthorhombic and tetragonal phases in the composition range of 0.02 ≤ x < 0.05 in this system is caused by the temperature of the polymorphic phase transition (PPT) decreasing to around room temperature but not the behavior of the morphotropic phase boundary (MPB). The samples near the coexistence region exhibit improved properties, which are as follows: piezoelectric constant d₃₃ = 155 pC/N, remnant polarization P_r = 24.2 μC/cm², and coercive electric field E_c = 2 kV/mm. The results indicate that although this kind of ceramics displays good properties, further study is needed to promote the stabilities of the ceramics in order to utilize them in varying temperature environments.     

Phase structure and enhanced piezoelectric properties in (1-x)(K0.48Na0.52)(Nb0.95Sb0.05)O3-x(Bi0.5Na0.42Li0.08)0.9Sr0.1ZrO3 lead-free piezoelectric ceramics

The piezoelectric properties of KNN lead-free piezoelectric ceramics could be greatly enhanced by forming multiphase coexistence. In this work, binary system (1-x)(K_0.48Na_0.52)(Nb_0.95Sb_0.05)O₃-x(Bi_0.5Na_0.42Li_0.08)_0.9Sr_0.1ZrO₃ [(abbreviated as (1-x)KNNS-xBNLSZ] ceramics with rhombohedral-tetragonal (r-T) phase boundary was designed and synthesized using the conventional solid-state sintering method, and effects of BNLSZ contents on their micrograph, phase structure and electrical properties were also investigated. According to phase diagram from the results of temperature-dependent capacitance and dielectric constant, the ceramics exhibit the R-T phase coexistence in the composition range of 3.5%≤x<4.5%, and an enhanced dielectric, ferroelectric, and piezoelectric behavior was obtained at such a phase boundary zone. As a result, the ceramics with x=0.04 exhibit optimum electrical properties of d₃₃~461 pC/N, k_p~46%, tan δ~0.03, P_r~16.9 μC/cm², and E_c ~9 kV/cm, together with a Curie temperature (T_C) of ~228 °C. Such a good comprehensive performance obtained in this present work is due to the R-T phase transition and enhanced ɛ_rP_r. It was believed that this ceramic system would promote the development of KNN-based lead-free ceramics.     

Boosting piezoelectric response of KNN-based ceramics with strong visible-light absorption

A series of (1 − x)(K_0.48Na_0.52)NbO₃-x(Bi_0.5Na_0.5)(Zr_0.55Ni_0.45)O_3-δ (KNN-BNZN) ceramics are designed to achieve excellent piezoelectric response along with narrow bandgap. The ceramics with x = 0.04 exhibit unprecedented piezoelectric coefficient d₃₃ ~ 318±10pC N⁻¹ in comparison with all reported narrow bandgap ceramics. A rhombohedral-orthorhombic-tetragonal (R-O-T) phase boundary is observed, indicating the formation of defect dipoles (Ni²⁺-) at morphotropic phase boundary region is desirable for piezo-/ferroelectric properties. In addition, a narrow bandgap ~2.5 eV along with gap states (~0.9 eV and ~1.6 eV) is obtained from the ceramics when x > 0.02, which can be persuasively explained by the schematic plot of bandgap splitting mechanism proposed in this work, where Ni 3d energy state plays a role as a scaffold in the process of electron transition. More importantly, largely enhanced photovoltaic performance of the ceramics is achieved under AM 1.5 irradiation. The NIR photoresponse property (maximum current density of ~100 nA cm⁻²) indicates such KNN-based ceramics with sub bandgap ~ 0.9 eV may even have potential to be applied in NIR light-activated devices. Our findings might pave way for the further development of piezoelectric/photoresponsive multifunctional devices.     

Large field-induced strain with enhanced temperature-stable dielectric properties of AgNbO3-modified (Bi0.5Na0.5)0.94Ba0.06TiO3 lead-free ceramics

(1-x)(Bi_0.5Na_0.5)_0.94Ba_0.06TiO₃-xAgNbO₃ lead-free piezoelectric ceramics (abbreviated as BNBT-100xAN) were prepared using the conventional solid-state sintering method. The effects of the introduction of AgNbO₃ (AN) dopants for the dielectric and piezoelectric performances of BNBT-100xAN ceramics were systematically studied. The XRD patterns and Raman spectra demonstrated that AN as a modifier was successfully diffused into the BNBT-100xAN lattice and revealed a pseudo-cubic symmetry structure. All samples exhibited a dense surface morphology accompanied by the uniform distribution of elements. A large bipolar strain of ~0.501% and unipolar strain of ~0.481% corresponding to the normalized strain d₃₃* of ~740 p.m./V were achieved for BNBT-1AN ceramic at 65 kV/cm field. The BNBT-4AN ceramic exhibited an excellent temperature-stable permittivity with the range from 59 to 380 °C and its dielectric loss was less than 0.02 between 97 °C and 329 °C. These results revealed that BNBT-100xAN ceramics were more hopeful candidates for actuators, strain sensors, and high-temperature capacitors.     

Ferroelectric,upconversion emission and optical thermometric properties of color-controllable Er3+-doped Pb(Mg1/3Nb2/3)O3-PbTiO3-Pb(Yb1/2Nb1/2)O3 ferroelectrics

The (0.98-x)(0.6Pb(Mg_1/3Nb_1/3)O₃-0.4PbTiO₃)-xPb(Yb_1/3Nb_1/3)O₃-0.02Pb(Er_1/2Nb_1/2)O₃ ((0.98-x)(PMN-PT)-xPYN:Er³⁺) ceramics were prepared through a solid-state reaction method. The phase structure, piezoelectric response, ferroelectric performance and upconversion emission of the ceramics were systematically investigated. The phase structure, the electrical and optical properties are strongly related to the content of PYN. The optimized piezoelectric response and upconversion emissions of the ceramics were achieved near x = 0.12, which locates in the morphotropic phase boundary (MPB) composition. Furthermore, the temperature sensing behaviors of the resultant compounds based on the thermally coupled levels of ²H_11/2 and ⁴S_3/2 of Er³⁺ ions in the temperature range of 133–573 K were studied by utilizing the fluorescence intensity ratio technique. Additionally, the thermal effect, which is induced by the laser pump power, of the studied ceramics is also investigated and the produced temperature is enhanced from 268 to 348 K with the pump power rising from 109 to 607 mW.     

Enhanced pyroelectric properties of lead-free BNT-BA-KNN ceramics for thermal energy harvesting

In this work, (1−x)(0.98Bi_0.5Na_0.5TiO₃-0.02BiAlO₃)-x(Na_0.5K_0.5)NbO₃ (BNT-BA-xKNN) lead-free pyroelectric ceramics were prepared by a solid-state reaction method. The effect of Na_0.5K_0.5NbO₃ (KNN) content on microstructure, phase transition, and electrical properties of the BNT-BA-xKNN ceramics were systematically investigated. The results show that the appropriate content of KNN can induce the formation of the tetragonal structure, which results in the decreased ferroelectric-antiferroelectric phase transition temperature as a result of the break of long-range translational symmetry of BNT lattices. Therefore, the ferroelectric and pyroelectric properties of the BNT-BA-xKNN near room temperature are improved. The room-temperature pyroelectric coefficient significantly increases from 3.66 × 10⁻⁴ C/m²/K at x = 0 to 8.04 × 10⁻⁴ C/m²/K at x = 0.02, making a great contribution to the superior pyroelectric energy harvesting. The output energy density in one cycle of the BNT-BA-0.02KNN is 23.32 μJ/cm³, which is twice as high as that of the pristine samples. The enhancement of material properties suggests that the pyroelectric energy harvesting can be efficiently optimized by the adequate control of the phase structure.     

Microstructure and electrical performance of Sm2O3-doped BCTSG lead-free ceramics

This work aims to upgrade the comprehensive electrical properties of BaTiO₃-based ceramics (1-x)[(Ba_0.94Ca_0.06)(Ti_0.92Sn_0.08)]-xSm₂O₃-0.06 mol% GeO₂ [abbreviated as (1-x)BCTS-xSm-0.06G]. First, piezoceramics were synthesized via a conventional solid-state method. Next, the phase structures, surface topographies, ferroelectric domains were evaluated using XRD, XRD Rietveld refinements, SEM, OP-PFM, TEM. The results demonstrate that all the ceramics possess an orthorhombic-tetragonal (O-T) phase when at room temperature. Significantly, optimized piezoelectricity is gained at x = 0.03 mol% (piezoelectric constant of d₃₃ = 630 ± 20 pC/N and planar electromechanical coupling factor of k_p = 61%). The ferroelectric domains of ceramics were examined using OP-PFM and TEM, which ulteriorly indicate that the favorable piezoelectricity is attributed to the coexistence of the O-T phase boundary and the subdued energy density of the domain wall. Furthermore, all the ceramics are confirmed to be relaxor ferroelectrics, with the relaxor degree increasing with the increasing content of Sm₂O₃.     

Effect of zirconium non-stoichiometry on phase structure and electrical properties of (K,Na)(Nb,Sb)O3-(Bi,Na)ZrO3 ceramics

As dopant, (Bi_0.5Na_0.5)ZrO₃ can significantly enhance electrical properties of KNN ceramics. However, certain issues in (K,Na)(Nb,Sb)O₃-(Bi,Na)ZrO₃ ceramics are still not well understood, one of which is the effect of zirconium non-stoichiometry on its electrical behaviors. Herein, 0.96(K_0.48Na_0.52)(Nb_0.96Sb_0.04)O₃-0.04(Bi_0.5Na_0.5)Zr_1+xO₃ (x = -0.02, -0.05, 0, 0.02, 0.05, 0.08) ceramics were prepared by pressureless sintering. The effect of zirconium ions non-stoichiometry on phase structure, domain structure and electrical behavior was explored. All ceramics had a pure perovskite structure with rhombohedral phase. The piezoelectric coefficient d₃₃, remanent polarization (P_r) and coercive electric field (E_C) reach the maximum (d₃₃ = 351 pC/N, E_C = 10.77 kV/cm and P_r = 24.26 μC/cm²) with x = 0.05. The results showed that the electric properties of the studied system can be significantly affects by trace zirconium. The appropriate excess of zirconium element would increase the concentration of oxygen vacancy, which could enhance the pinning effect of the domain walls and increase E_C and P_r correspondingly. The domain structure characterized by PFM technology further confirms the macroscopic results. Moreover, a defect switching model was proposed to probe into the effect of defects on their performances. Thus, it is believed that this work would provide a new strategy for further optimizing the comprehensive properties of binary or multivariate KNN-based ceramics.     

Enhanced piezoelectric properties and temperature-insensitive strain behavior of <001>-textured KNN-based ceramics

In this study, <001>-textured 0.99(K_0.5Na_0.5)_0.95Li_0.05Nb_0.93Sb_0.07O₃−0.01CaZrO₃ [abbreviated as 0.99KNLNS-0.01CZ] lead-free ceramics were prepared by templated grain growth (TGG) using plate-like NaNbO₃ templates and sintered by a two-step sintering process with different soaking time. All textured samples with high Lotgering factor (f >85%) presented orthorhombic and tetragonal coexisting phase, and the proportion of orthorhombic phase was varied with prolonged soaking time. A large piezoelectric constant d₃₃ (~ 310 pC/N) was obtained in the textured samples with a 12 h soaking time, which was almost twice larger compared to the randomly oriented one. Furthermore, the field-induced piezoelectric strain coefficient d₃₃^*(~ 440 pm/V) of the textured ceramics with 6 h soaking time was larger than the value of randomly oriented one (~ 298 pm/V) at room-temperature. Enhanced piezoelectric response and good temperature stability prove that <001>-textured 0.99KNLNS-0.01CZ ceramics are promising candidates in the field of lead-free piezoelectric materials.     

Temperature stability and phase transition of Li0.02(KxNa1−x)0.98NbO3 ceramics

Li_0.02(K_xNa_1?x)_0.98NbO₃(x = 0.35–0.55) ceramics were prepared using the conventional solid state sintering method. The thermal behaviors of Li-modified (K_xNa_1?x)NbO₃ ceramics were investigated from ?30 to 150 °C, and the effect of Na/K ratio in (K_xNa_1?x)NbO₃ ceramics on thermal behavior and electrical properties was also studied. In the case of Li_0.02(K_xNa_1?x)_0.98NbO₃ ceramics with 0.5 wt.% ZnO, the transition temperature was sharply decreased because of a phase transition as the composition range of x was 0.425–0.475. From the results of the temperature dependence of piezoelectric properties, it is assumed that the Na-rich phase is less stable than the K-rich phase for temperature change.     

Electrical properties and temperature stability of SrTiO3-modified (Bi1/2Na1/2)TiO3-BaTiO3-(K1/2Na1/2)NbO3 piezoceramics

SrTiO₃-modified lead-free piezoelectric ceramics, (0.93-x)Bi_0.5Na_0.5TiO₃-xSrTiO₃-0.06BaTiO₃-0.01 K_0.5Na_0.5NbO₃ [(BNT-xST)-BT-KNN, x = 0-0.06], were prepared using a conventional solid-state reaction method. The XRD structure analysis and electric properties characteristics revealed the ST-induced phase transformation from the ferroelectric phase to the relaxor phase and their coexistence state. Benefiting from the ST-destructed ferroelectric long-range orders, the high normalized strain value of 600 pm/V was obtained in the (BNT-0.02ST)-BT-KNN ceramic at 5 kV/mm. The ST-generated relaxor phase was found to have a constructive effect on improving the temperature stability and restraining the hysteresis of the electric-field-induced strain. The normalized strain of (BNT-0.06ST)-BT-KNN ceramics could be kept at a high value ~337 pm/V at elevated temperature up to 120°C.