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In this study, the stabilization of ergodicity and electromechanical strain properties of lead‐free ternary 0.75Na1/2Bi1/2TiO3–0.24SrTiO3–0.01ABO3 piezoceramics (BNT–24ST, ABO3 = BaZrO3 (BZ), CaTiO3 (CT), and BiFeO3 (BF)) were investigated. The relaxor state could be stabilized in BZ‐and BF‐modified BNT–24ST ceramics even at room temperature, whereas pure BNT–24ST and CT‐modified ceramics exhibited ferroelectric (FE) behavior. These phenomena were rationalized by analyzing the temperature‐dependent permittivity; detecting the FE‐relaxor phase transition temperature (TF‐R); and investigating features in strain, polarization, and switching current curves. Furthermore, high‐temperature conductivity data showed that relaxor behavior and realization of large strain properties strongly correlated with the concentration of oxygen vacancies in ABO3‐modified BNT–ST ternary systems. [ABSTRACT FROM AUTHOR]

The 0.74Na1/2Bi1/2TiO3–0.26SrTiO3 codoped with Li2CO3 and B2O3 is studied to develop the low‐temperature sintered lead‐free piezoceramic for multilayer applications. The studied piezoceramics are synthesized by a conventional solid‐state reaction method. Their crystal structures, microstructures, ferroelectrics, and strain properties are analyzed. Interestingly, the addition of Li2CO3 and B2O3 reduces the sintering temperature of the 0.74Na1/2Bi1/2TiO3–0.26SrTiO3 sample from 1175 to 975 °C. All samples show a pseudocubic perovskite structure with a dense microstructure and an inhomogeneous grain size distribution. The electric‐field‐induced polarization loops of the samples are saturated at 4 kV mm−1. More importantly, the 0.74Na1/2Bi1/2TiO3–0.26SrTiO3 + 1 wt%Li2CO3 + 1 wt%B2O3 sample sintered at 975 °C shows a Smax/Emax value of 510 pm/V under an applied electric field of 2 kV mm−1, which is promising for multilayer lead‐free piezoelectric actuator applications. [ABSTRACT FROM AUTHOR]

This study investigated the effects of CaTiO3, BaTiO3, and BaZrO3 doping on the phase transition and strain properties of lead-free 0.76Bi1/2Na1/2TiO3-0.24SrTiO3 (BNT-24ST) piezoceramics. The nonergodicity of the BNT-24ST ceramic was stabilized as a function of CaTiO3 doping, corresponding to the existence of the ferroelectric-to-relaxor phase transition temperature (TF-R) peak in the dielectric permittivity curves of the samples. However, the BaTiO3- or BaZrO3- doped NBT-24ST samples promote the transition from a nonergodic to an ergodic relaxor phase. The 0.01 mol BaTiO3 or 0.01 mol BaZrO3 doping decreases the TF-R peak of the NBT-24ST sample to below room temperature. Interestingly, it is noted that the nonergodic-to-ergodic relaxor phase transition of the BaTiO3-doped BNT-24ST ceramics was faster than that of the BaZrO3-doped BNT-24ST ceramics. The 0.01 mol BaTiO3-doped BNT-24ST sample presents a maximum dielectric constant of ~ 8000. The maximum piezoelectric actuator coefficient (uni-Smax/Emax) of ~ 525 pm/V was observed for the 0.01 mol BaTiO3-doped BNT-24ST ceramic. The effect of the tolerance factor on the phase transition and electrical properties of the BNT-24ST-ABO3 ceramics is suggested. [ABSTRACT FROM AUTHOR]

The stabilization of ergodicity plays an important role in realizing large strain in a Bi1/2Na1/2TiO3 (BNT)‐based relaxor, which is strongly related to the degree of random fields with respect to the randomly distributed different cations. To clarify the effects of different ionic radii, this study investigated and compared the microstructures, crystal structures, phase transition behaviors, and electrical properties of BNT–ST‐based ternary ceramics by modifying BiMeO3 (where Me = Al and Fe). It was observed that the stabilized relaxor states are different between BiFeO3‐/and BiAlO3‐modified BNT–ST ternary ceramics. As a result, it is suggested that phase transition (more precisely, the stabilization of ergodicity) can be influenced by the different internal strain in BNT–ST‐based ternary ceramics. [ABSTRACT FROM AUTHOR]

Fabrication of 0.74(Bi0.5Na0.5)TiO3-0.26SrTiO3 (abbreviated as BNST26) ceramics via both conventional furnace sintering (CFS) and microwave sintering (MWS) was investigated in this work. MWS at 1100°C for 5 min resulted in ceramic with density comparable to that of ceramic fabricated via CFS at 1175°C for 2 h. Average grain sizes of 3.2 μm and 2.4 μm were calculated for the ceramics prepared by CFS and MWS, respectively, which was attributed to the lower temperature and shorter sintering time for MWS compared with CFS. In order to investigate the effect of sintering method on the electrical properties of the prepared ceramics, the polarization hysteresis, bipolar and unipolar strain curves, and temperature dependence of permittivity were explored. The results revealed that the remanent polarization (Pr) and coercive field (Ec) of the ceramic prepared by MWS at 1100°C for 5 min were comparable to those of the ceramic under CFS at 1175°C for 2 h. However, the maximum polarization (Pmax) of the CFS ceramic was higher than that of the MWS ceramic. In the case of electric field-induced strain, there was no considerable difference between the MWS and CFS ceramics, and normalized strain d33* = 501 pm/V was obtained for the MWS ceramic at 1100°C, indicating the effectiveness of MWS for fabrication of BNT-based piezoceramics at lower temperature and shorter time versus CFS. [ABSTRACT FROM AUTHOR]

Lead-free (1−x) K0.5Na0.5NbO3−xSrTiO3 (KNN-100xST) piezoelectric ceramics were prepared using a conventional solid-state reaction method to investigate their phase-transition behavior and electrical properties. SrTiO3 modification is known to improve the piezoelectric properties and sinterability of lead-free KNN ceramics. Previous studies on SrTiO3-modified KNN ceramics have mainly focused on enhancements to the dielectric and piezoelectric properties using an orthorhombic–tetragonal phase transition concept. However, the electromechanical strain behavior near this phase boundary remains challenging. In this work, a polymorphic phase boundary between the orthorhombic and tetragonal phases was found at 5 mol% of SrTiO3 content, where an enhanced piezoelectric constant (d33) was observed. In addition, normalized strain (d*33) was obtained from the unipolar strain at 4 kV/mm, which reached the highest value of 210 pm/V in KNN-5ST ceramics. [ABSTRACT FROM AUTHOR]

The 0.93(Bi0.5Na0.5)TiO3-0.07BaTiO3 doped with different amount of (Ga0.5Ta0.5)4+ complex-ion from 0 to 4 mol% (abbreviated as BNBT-100xGT) ceramics were prepared. Phase analysis revealed that up to x = 0.035, Ga3+ and Ta5+ completely dissolve in BNBT perovskite structure and substitute in B-site. Increase in x more than 0.02 resulted in formation of pinched P-E loops accompanied by sharp decrease in Pr. This observation can be attributed to the phase transition from ferroelectric (FE) to a non-polar ergodic relaxor (ER) which could be transformed reversibly to a FE phase by applying an electric field. According to temperature-dependence dielectric constant results, transition temperature from FE to ER phase decreased and for ceramic with x = 0.03 shifted to lower than room temperature with increasing GT content. As a result, enhanced unipolar electric field-induced strain (0.4% under 60 kV/cm) corresponding to d33* of 667 pm/V was obtained in this ceramic. The large electrostrain is accompanied with relatively large hysteresis, which should be lowered for actuator applications. However (Ga0.5Ta0.5)4+ complex-ion doping of BNT-based ceramics, could be considered as an efficient approach to enhance electrical properties, especially electrostrain characteristic of these ceramics, as competitive alternatives to lead-based ceramics. [ABSTRACT FROM AUTHOR]

The formation of a morphotropic phase boundary (MPB) in piezoelectric ceramics is one of the most important techniques to enhance their dielectric and piezoelectric properties. In this work, a rhombohedral (R) and tetragonal (T) phase boundary has been designed and clarified using the lead‒free 0.92(Na0.5K0.5)NbO3–(0.08–x)(Bi0.5Li0.5)TiO3–xBaZrO3 ternary system. The R-T phase coexistence region is identified in the ceramics with 0.06 ≤ x ≤ 0.07. We successfully demonstrated that the crystal's relatively enhanced d33 and its excellent temperature stability are originated from phase transition behaviors that were confirmed by the temperature‒dependent dielectric properties and X−ray diffraction (XRD) patterns. [ABSTRACT FROM AUTHOR]

Dielectric, ferroelectric, piezoelectric, and strain properties of lead-free Sn-doped Bi1/2(Na0.82K0.18)1/2TiO3 (BNKT) were investigated. A crossover from a nonergodic relaxor to an ergodic relaxor state at room temperature, accompanied by a giant electric-field-induced strain, was observed at 5 at. % Sn doping. Switching dynamics monitored during a bipolar poling cycle manifested that the observed giant strain originates from incipient piezoelectricity. When Sn doping level reached 8 at. %, BNKT exhibited an electrostrictive behavior with a highly temperature-insensitive electrostrictive coefficient of Q11 = 0.023 m4 C-2. [ABSTRACT FROM AUTHOR]