Total scattering and diffraction studies of lead-free piezoelectric (1-x)Ba(Zr _0.2 Ti _0.8 )O ₃ -x(Ba _0.7 Ca _0.3 )TiO ₃ deconvolute intrinsic and extrinsic contributions to electromechanical strain

The piezoelectric material (1-x)Ba(Zr _0.2 Ti _0.8 )O ₃ -x(Ba _0.7 Ca _0.3 )TiO ₃ (BZT-xBCT) has emerged as a leading lead-free candidate to replace Pb(Zr _1-x Ti _x )O ₃ (PZT) for certain applications. However, the structural response of BZT-xBCT to an electric field is not well understood, particularly how the local structure responds to varying electric fields. In this study, in situ synchrotron X-ray diffraction and total scattering measurements were performed on BZT-xBCT from x = 0.45 to 0.60. The lattice distortions were quantified from the unit cell parameters for the compositions in the orthorhombic (O) region (x = 0.45 to 0.50) and tetragonal (T) region (x = 0.51 to 0.60). It was found that the lattice distortion is minimized in compositions that exhibit the largest effective piezoelectric effect, particularly at the x = 0.45 composition (between the rhombohedral (R) and O regions) and at the morphotropic phase boundary (MPB) composition x = 0.50 (between O and T regions). The degree of domain wall motion was quantified, and the results indicate that as the MPB is approached, the degree of domain wall motion increases dramatically. The increase in domain wall motion also coincides with the minimization of the lattice distortion. The pair distribution functions (PDFs) were calculated from the Fourier transform of the total scattering data. Analysis of the PDF peak shifts with electric field shows nonlinear lattice strains across all compositions, which indicates a deviation from classical piezoelectric behavior. We conclude that the strong piezoelectric properties in the BZT-xBCT system are attributed to an increased degree of domain wall reorientation that is facilitated by a decreased lattice distortion.