Domain wall motion and electromechanical strain in lead-free piezoelectrics: Insight from the model system (1-x)Ba(Zr0.2Ti0.8)O3-x(Ba0.7Ca0.3)TiO3 using in situ high-energy X-ray diffraction during application of electric fields

The piezoelectric compositions (1 - x)Ba(Zr0.2Ti0.8)O-3-x(Ba0.7Ca0.3)TiO3 (BZT-xBCT) span a model lead-free morphotropic phase boundary (MPB) between room temperature rhombohedral and tetragonal phases at approximately x = 0.5. In the present work, in situ X-ray diffraction measurements during electric field application are used to elucidate the origin of electromechanical strain in several compositions spanning the tetragonal compositional range 0.6 <= x <= 0.9. As BCT concentration decreases towards the MPB, the tetragonal distortion (given by c/a-1) decreases concomitantly with an increase in 90 degrees domain wall motion. The increase in observed macroscopic strain is predominantly attributed to the increased contribution from 90 degrees domain wall motion. The results demonstrate that domain wall motion is a significant factor in achieving high strain and piezoelectric coefficients in lead-free polycrystalline piezoelectrics. (C) 2014 AIP Publishing LLC.