Unique freezing dynamics of flexible guest cations in the first molecular postperovskite ferroelectric: (c5h13nbr)[mn(n(cn)2)3]

Abstract

Ferroelectricity is usually found in cubic and hexagonal perovskites consisting of corner- and faced-shared BX6 octahedra, respectively. In contrast, another important branch of perovskites, postperovskites, which contain layers constructed by both edge- and corner-shared BX6 octahedra, have been much more scarcely studied and virtually absent in the fields of ferroelectricity since the discovery of postperovskite structure in 1965. In this study, we present for the first time a molecular postperovskite ferroelectric, (bromocholine) [Mn(N(CN)2)3], and demonstrate how spontaneous polarization arises from the freezing dynamics of bromocholine cations in a unique space confined by postperovskite layers. These findings suggest that postperovskites could serve as a new type of host- guest model in controlling the molecular dynamics of abundant polar cations in the development of novel ferroelectric materials.