Temperature-driven phase transitions in SrBi2Ta2O9 from first-principles calculations

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

APPLIED PHYSICS LETTERS

AMER INST PHYSICS

Año: 2008 vol. 93 p. 2429011 - 2429023

0003-6951

<!-- @page { size: 21cm 29.7cm; margin: 2cm } P { margin-bottom: 0.21cm } --> The thermal phase transition sequence of SrBi2Ta2O9 is investigated using a shell model approach 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, corroborating the existence of an intermediate paraelectric phase between the high-symmetry tetragonal and the ferroelectric phase. The intermediate phase is orthorhombic and it is characterized by the rotation of the TaO6 octahedra around the a-axis. We show that this phase can be also detected from the dielectric response of the material. The present approach constitutes a powerful tool for a theoretical prediction of intermediate phases, not yet observed experimentally, in other Aurivillius compounds.