Abstract
We report the observation of an antipolar phase in cubic driven by an unconventional microscopic mechanism, the cooperative Jahn-Teller effect of molecular clusters. The assignment of the antipolar nature is based on sudden changes in the crystal structure and a strong drop of the dielectric constant at , also indicating the first-order nature of the transition. In addition, we found that local symmetry lowering precedes long-range orbital ordering, implying the presence of a dynamic Jahn-Teller effect in the cubic phase above . Based on the variety of structural polymorphs reported in lacunar spinels, also including ferroelectric phases, we argue that may be transformable to a ferroelectric state, which would further classify the observed antipolar phase as antiferroelectric.
- Received 16 September 2020
- Revised 2 March 2021
- Accepted 8 April 2021
DOI:https://doi.org/10.1103/PhysRevLett.126.187601
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