Ferroelectric Phase Transition and New Intermediate Phase in Bi-Layered Perovskite SrBi 2 Ta 2 O 9

Abstract

Thermal and structural studies showed that SrBi 2 Ta 2 O 9 undergoes ferroelectric-intermediate and intermediate-paraelectric phase transitions at 608 K ( T c ) and 850 K ( T *), respectively, while Bi-rich Sr 0.85 Bi 2.1 Ta 2 O 9 at 510 K ( T o ) and 670 K ( T c ). On heating, SrBi 2 Ta 2 O 9 still remains to be orthorhombic above T c, and then changes to tetragonal above T *. The TaO 6 is a distorted octaheron along the c -axis even in the paraelectric phase, and locates in antiparallel manner above T *. Below T c, this crystal favors canted arrangements of TaO 6, resulting in the net polarization along the a -axis. It was clarified that SrBi 2 Ta 2 O 9 shows a canted weak ferroelectricity, analogous to weak ferromagnetism with Dzialoshinski-Moriya interaction. Keywords: Layered PerovskiteSbtFerroelectricPhase TransitionCrystal Structure