Proper Ferroelectricity in the Dion-Jacobson Material CsBi2Ti2NbO10: Experiment and Theory

A diverse range of materials and properties are exhibited by layered perovskites. We report on the synthesis, characterization, and computational investigation of a new ferroelectric-CsBi2Ti2NbO10-an n = 3 member of the Dion-Jacobson (DJ) family. Structural studies using variable-temperature neutron powder diffraction indicate that a combination of octahedral rotations and polar displacements result in the polar structure. Density functional theory calculations reveal that the wider perovskite blocks in CsBi2Ti2NbO0 stabilize proper ferroelectricity, in contrast to the hybrid-improper ferroelectricity reported for all other DJ phases. Our results raise the possibility of a new class of proper ferroelectric materials analogous to the well-known Aurivillius phases.