Local and long range polar order in the relaxor-ferroelectric compounds PbMg 1 / 3 Nb 2 / 3 O 3 and PbMg 0.3 Nb 0.6 Ti 0.1 O 3

TLDR: In this paper, the structural evolution of PMN/PT10% and PMN (PbMg 0. 3 Nb 0. 6 Ti 0. 1 O 3 ) was studied and compared using high-resolution x-ray and neutron diffraction.

Abstract: Structural evolutions of PMN/PT10% (PbMg 0 . 3 Nb 0 . 6 Ti 0 . 1 O 3 ) and PMN (PbMg 1 / 3 Nb 2 / 3 O 3 ) are studied and compared using high-resolution x-ray and neutron diffraction. At high temperature, PMN-like diffuse scattering, associated with local disordered shifts, is evidenced by PMN/PT10%. A part of this intensity condenses at T c =285 K when PMN/PT10% exhibits a structural phase transition toward a long-range rhombohedral phase, whereas in PMN the polar order remains short ranged. In the ferroelectric phase of PMN/PT10% local [100] displacements of lead are evidenced, and are connected to the observation of diffuse scattering far below T c . The local symmetry in which oxygen and Ti/Mg/Nb cations are shifted along the [111] direction, but in which the lead atoms are shifted along one of the tetragonal [100] directions is monoclinic. This short-range polar order reconstructs on average a polar rhombohedral symmetry. A global picture for the structural evolution in the PMN/PT compounds is proposed. It is based on competition between rhombohedral and tetragonal polar order, which connects the relaxation properties of PMN and the high piezoelectric response of morphotropic monoclinic PMN/PT with a high concentration of PT.