Octahedral Tilt Instability of ReO_3-type Crystals

TL;DR

This paper investigates the octahedral tilt transitions in ReO_3-type crystals, revealing the role of long-range dipole interactions and electrostatic energy in driving structural phase changes.

Contribution

It introduces a mechanism involving long-range dipole-dipole forces and electrostatic energy gain as key factors in octahedral tilt transitions.

Findings

Long-range dipole-dipole interactions influence tilt transitions.

Electrostatic (Madelung) energy gain stabilizes tilted structures.

Unit cell shrinks due to ionic sphere tilting enhances electrostatic effects.

Abstract

The octahedron tilt transitions of ABX_3 perovskite-structure materials lead to an anti-polar (or antiferroelectric) arrangement of dipoles, with the low temperature structure having six sublattices polarized along various crystallographic directions. It is shown that an important mechanism driving the transition is long range dipole-dipole forces acting on both displacive and induced parts of the anion dipole. This acts in concert with short range repulsion, allowing a gain of electrostatic (Madelung) energy, both dipole-dipole and charge-charge, because the unit cell shrinks when the hard ionic spheres of the rigid octahedron tilt out of linear alignment.