An electron diffraction and Monte Carlo simulation study of diffuse scattering in Pb(Zr,Ti)O₃

Transverse polarized diffuse streaks have been recorded via transmission electron microscopy for a range of Pb(Zr_1-xTi_x)O ₃ ceramics spanning the entire phase diagram from the rhombohedral phase (x = 0.3), through the monoclinic morphotropic phase boundary region (MPB; x = 0.48) to the tetragonal phase (x = 0.7). Although the same type of streaks are observed over the whole composition range, they are strongest and most distinct in the rhombohedral phase and diminish in clarity as the MPB is approached. The streaks have been shown to correspond to diffuse planes of scattering in three dimensions and are oriented normal to the (cubic) 〈111〉_c directions. A Monte Carlo computer simulation model has been developed that convincingly reproduces the observed diffraction patterns in the rhombohedral phase. In this model the displacements of Pb ions in chains running along each of the 〈111〉_c directions are directed along the chain and are strongly correlated from cell to cell. There is no evidence of lateral correlation, indicating that neighbouring chains are essentially independent.