\(Bi 2 W 2 O 9 \): A potentially antiferroelectric Aurivillius phase

Ferroelectric tungsten-based Aurivillius oxides are naturally stable superlattice structures, in which A -site deficient perovskite blocks [ W n O 3 n + 1 ] − 2 ( n = 1 , 2 , 3 , ⋯ ) interleave with fluorite-like bismuth oxide layers [ Bi 2 O 2 ] + 2 along the c -axis. In the n = 2 Bi 2 W 2 O 9 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 P n a b symmetry. We explore the energetics of metastable phases and the potential for antiferroelectricity in this n = 2 Aurivillius phase.