Thermally stable electrostrains of morphotropic 0.875NaNbO3-0.1BaTiO3-0.025CaZrO3 lead-free piezoelectric ceramics

The 0.875NaNbO3-0.1BaTiO3-0.025CaZrO3 relaxor ferroelectric ceramics were reported to exhibit thermally stable electrostrains (∼0.15% @ 6 kV/mm) from room temperature (RT) to ∼175 °C and comparable strain hysteresis (<13%) to that of typical lead-based piezoelectric ceramics. Dominant strain contribution mechanisms with increasing temperature were analyzed by means of temperature-dependent permittivity, polarization, and strain measurements and synchrotron x-ray diffraction. The rhombohedral (R) and tetragonal (T) morphotropic phase boundary provided a solid structural base for temperature-stable piezoelectric strains from RT to ∼140 °C. The growth of polar nanoregions (pseudocubic) into microdomains (R) and subsequent field-induced R-T phase transition, as well as large electrostrictive effects, sequentially contributed to high electrostrain levels in the proximity of the Curie temperature (from 140 to 175 °C). In addition, the observed low strain hysteresis was attributed to the small strain fraction from domain switching. These experimental results demonstrated that NaNbO3-based relaxor ferroelectrics might be potential lead-free materials for actuator applications.