Finite-temperature properties of PMN-PT from atomistic simulations*

Relaxor-based single crystals such as (PbMg$_{1/3}$Nb$_{2/3}$O$_{3})_{1-x}$-(PbTiO$_{3})_{x }$(denoted as PMN-PT) have been reported to exhibit excellent electromechanical properties. The high electromechanical performance characteristics of the relaxor-PT solid solutions is found for compositions at or near the morphotropic phase boundary (MPB) separating the rhombohedral and tetragonal phases. In addition to this MPB area, PMN-PT solid solutions are very interesting and complex to mimic because one of its end-member (PMN) is considered as the prototype of relaxors while its other end-member (PT) is a prototype of classical ferroelectrics. In this work, we developed an effective Hamiltonian technique to theoretically investigate the MPB area of PMN-PT and the symmetries of its phases and to reveal the effect of atomic ordering on physical properties of PMN-PT. If time allows, we will also discuss the effect of oxygen vacancies on the finite-temperature properties of PMN-PT.