A high energy synchrotron x-ray study of crystallographic texture and lattice strain in soft lead zirconate titanate ceramics

The lattice parameters and crystallographic texture in La, Sr-doped soft lead zirconate titanate ceramics were examined using high-energy synchrotron x-ray diffraction. The preferred orientations in poled tetragonal and rhombohedral ceramics near the morphotropic phase boundary, caused by ferroelectric domain switching, were determined by monitoring the (002)∕(200) and (111)∕(111¯) intensity ratios, respectively. The lattice strains were also monitored using the {111} and {200} plane spacings in tetragonal and rhombohedral ceramics, respectively. The diffraction experiments were carried out in transmission, enabling the true “bulk” state to be characterized. It was observed that for the tetragonal phase both the lattice spacing d{111} and the intensity ratio R{200} varied linearly as a function of sin2Ψ,Ψ being the angle between the plane normal and the macroscopic polar axis. Similar observations were made for d{200} and R{111} in rhombohedral ceramics. The results are interpreted in terms of the remanent macroscopic strain state due to poling and the resulting relative misfit between any given grain and the surrounding matrix, which creates significant intergranular stresses. The tetragonal {111} and rhombohedral {200} plane spacings were identified as important monitors of intergranular stress, since the elongation of a grain along the tetragonal ⟨111⟩ or rhombohedral ⟨200⟩ directions, respectively (due to non-180° domain wall motion), is zero in the absence of the constraint imposed by neighboring grains. As a result, the tetragonal {111} or rhombohedral {200} reflections are sensitive only to the macrostrain of the polycrystal. It is proposed that the nonlinear and hysteretic piezoelectric response of the lattice strain reported in previous studies is primarily a result of coupling between the extrinsic non-180° ferroelectric domain switching mechanisms and the intrinsic lattice strain.