Intermediate phase and dynamics of the ferroelectric transition in SrBi2Ta2O9

R. MACHADO; M. SEPLIARSKY; M.G.STACHIOTTI

Xia an, China

Congreso; The joint meeting of 12th International Meeting on Ferroelectricity and 18th IEEE International Symposium on Applications of Ferroelectrics; 2009

<!-- @page { margin: 2cm } P { margin-bottom: 0.21cm } --> The phase transition sequence and the dynamical nature of the ferroelectric transition in SrBi2Ta2O9 (SBT) are investigated using a shell model with parameters fitted to first-principles calculations. We show that the complex interplay between polar and nonpolar instabilities leads to the presence of two phase transitions in SBT. In this way the existence of an intermediate orthorhombic paraelectric phase between the high-symmetry tetragonal and the ferroelectric phase is demonstrated without using any explicit experimental data as input. This phase naturally emerges from the simulated phase diagram, and it is characterized by the rotation of the TaO6 octahedra around the a-axis. The present approach constitutes a powerful tool for a theoretical prediction of intermediate phases, not yet observed experimentally, in other Aurivillius compounds. Finally, we report the displacive and order-disorder characters of SBT analyzed from the local microscopic dynamics.