Bi2W2O9: A potentially antiferroelectric Aurivillius phase

Ferroelectric tungsten-based Aurivillius oxides are naturally stable superlattice structures, in which A-site deficient perovskite blocks [WnO3n+1]−2 (n=1,2,3,⋯) interleave with fluorite-like bismuth oxide layers [Bi2O2]+2 along the c-axis. In the n=2Bi2W2O9 phase, an in-plane antipolar distortion dominates but there has been controversy as to the ground-state symmetry. Here we show, using a combination of first-principles density functional theory calculations and experiments, that the ground state is a nonpolar phase of Pnab symmetry. We explore the energetics of metastable phases and the potential for antiferroelectricity in this n=2 Aurivillius phase.