Thermally Induced Bi(III) Lone Pair Stereoactivity: Ferroelectric Phase Transition and Semiconducting Properties of (MV)BiBr₅ (MV= methylviologen)

Abstract

Regular BiBr5 chains of trans-connected octahedra are stabilized by methyviologen cations. The Bi3+ electron lone pair is sterochemically activated below −30 °C, leading to an acentric polar phase, and this is correlated with an increase of the band gap, and with the transfer from a para- to a ferroelectric phase.