Symmetry of domains in morphotropic PbZr1-xTixO3 ceramics

PbZr1-xTixO3 (PZT) ceramic samples with compositions over the morphotropic phase boundary (MPB) ranging from 45/55 to 60/40 [(1 - x)/x] are studied by transmission electron microscopy combined with convergent-beam electron diffraction (CBED). All point-group symmetries debated for morphotropic PZT, 4mm, m, and 3m, are identified. Up to PZT 54/46 the symmetry is mainly tetragonal within lamellar domain configurations. From PZT 52/48 to PZT 54/46 nanodomains evolve within the tetragonal microdomains and monoclinic symmetry is identified within the same domain configurations, together with tetragonal symmetry for PZT 54/46. For PZT 55/45 up to PZT 60/40 rhombohedral symmetry is observed. Rhombohedral domains, as identified by CBED, are characterized by their width, curved domain walls, and grainy inner contrast. This contrast, together with anisotropic first-order Laue-zone intensities, implies that local deviations from 3m symmetry may exist within rhombohedral domains. Between PZT 54/46 and PZT 55/45 the morphology of the microdomains changes abruptly. For PZT 54.5/45.5 both types of domain configurations coexist within the same grain. For PZT 56/44 a tetragonal inclusion within a rhombohedral matrix is identified by CBED. On the other side of the MPB, domains with a rhombohedral appearance are found in PZT 53.5/46.5. These observation were less frequent but show that coexistence is present in ceramic samples around the MPB.