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( Ba, Ca)( Ti, Zr) O3 lead-free piezoelectric ceramics have been considered to be one of the most potential lead-free alternatives for PZT in the room-temperature range. The stability of the piezoelectric performance during unipolar cycling is investigated in this study. It is found that the unipolar fatigue behavior is similar to soft PZT. Developments of bias field, offset polarization, asymmetry in strain, and dielectric hysteresis loops are observed during bipolar measurements. The changes are mainly contributed to the migration of charge carriers to the grain boundaries driven by the unscreened depolarization field. Redistribution of the accumulated charge carriers by bipolar electric cycling or thermal annealing can significantly recover the unipolar fatigued state. The unipolar strain response stabilized after 1000 cycles at 0.053% for an electric field of 0.6 kV/mm ( d33*= 883 pm/V), which is a good characteristic for actuator applications. [ABSTRACT FROM AUTHOR]

High piezoelectric properties are desired for lead-free piezoelectric materials in consideration as a replacement for lead-based materials in applications. Due to the high piezoelectric coefficient, ( Ba100− x Ca x) ( Ti100− y Zr y) O3 ( BCTZ) piezoelectric ceramics have been considered as a promising lead-free alternate piezoelectric material. Here, six compositions were selected based on a prediction that all the compositions would have high piezoelectric coefficient at room temperature. The results confirmed all compositions exhibit well developed hysteresis loops and a large piezoelectric coefficient at room temperature. This is due to the coexistence of several phases where the major phase is likely to be orthorhombic and the second phase is proposed to be tetragonal. The phase transition was found to occur over a broad temperature range instead of at a specific temperature only. A relationship between the tetragonal-orthorhombic phase transition temperature and Ca2+ and Zr4+ content was proposed. This enables clear determination of BCTZ compositions with high piezoelectric coefficient at a desired operation temperature. [ABSTRACT FROM AUTHOR]

(K,Na)NbO3 (KNN) is a promising lead‐free ferroelectric/piezoelectric system, to which incorporating BaZrO3 can greatly enhance its piezoelectricity, but the mechanism is not clear. This work was conducted to investigate the phase transition in the BaZrO3‐modifed KNN system and its contribution to piezoelectricity enhancement, using thin films with a fixed orientation and high compositional homogeneity fabricated by a sol‐gel method. Two ferroelectric‐to‐ferroelectric phase transitions are revealed, which correspond to monoclinic MC‐ MA phase transition at higher temperature and rhombohedral‐monoclinic MC phase transition at lower temperature. It is difficult to distinguish these phases in KNN‐based bulk materials, but their differences are clear when conducting high‐resolution X‐ray reciprocal space mapping (RSM) on the present thin films. Piezoresponse force microscopy experiments also revealed an interesting finding that local piezoelectricity of monoclinic phases was higher than that of rhombohedral ones in KNN‐based thin films. This work could shed insights on the fundamental understandings for the effect of the chemical doping, and offer guidance for property optimization in the KNN‐based lead‐free piezoelectrics. Phase transition and piezoelectricity were modified in (K,Na)NbO3 based lead‐free piezoelectric thin films, where the R to monoclinic MC phase transition temperature was elevated with increasing BaZrO3 doping levels and the local piezoelectricity reached the maximum value at the phase boundary. [ABSTRACT FROM AUTHOR]