(c) Higher symmetry

Since the volume of a polyhedron increases upon distortion, high pressures favor symmetric coordination environments. This can lead to the suppression of ferroelectric ion shifts, electronically driven Jahn -Teller distortions, and stereoactive electron lone pair effects on 6s² cations, such as
Tl ⁺, Pb²⁺ & Bi³⁺. As an example of this the compound PbSnO₃, with the perovskite structure, can only be made using high pressure. Ambient pressure synthesis leads to a mixture of PbO (with a pronounced Pb²⁺ lone pair effect) and SnO₂.