Ab initio supported model simulations of ferroelectric perovskites

M. SEPLIARSKY; M. G. STACHIOTTI; R. L. MIGONI

COMPUTATIONAL MATERIALS SCIENCE

ELSEVIER SCIENCE BV

Lugar: Amsterdam; Año: 1998 vol. 10 p. 51 - 56

0927-0256

While ferroelectric KNbO3 and BaTiO3 present the cubic-tetragonal-orthorhombic-rhombohedral phase sequence with decreasing T, their related compounds KTaO3 and SrTiO3 are incipient ferroelectrics which exhibit the ferroelectric soft mode but remain paraelectric up to 0 K. Despite the large amount of research attracted by the above phenomenology since long ago, quite a few realistic model simulations are available. Many lattice dynamical calculations have been performed for each isolated material, but the only unified view of their ferroelectric behavior has been provided by the nonlinear oxygen polarizability model. Although initially based on phonon data for the cubic phase, recent ab initio calculations confirm that the model is basically correct with regards to the energetics involved in the various ferroelectric distortions in KNbO3. Our molecular dynamics simulations show the crossover from a soft mode to an order-disorder dynamics in the cubic phase of KNbO3, the appearance of its various ferroelectric phases, and the soft-mode behavior of KTaO3.