Unusual Two–step Switchable Dielectric Behaviors and FerroelasticPhase Transition in a Simple 18‐Crown‐6 Clathrate

Abstract

AbstractThe molecular multi‐sequential phase transition accompanying with perfect switchable dielectric behaviors and ferroelastic properties are seldom reported. Here we investigated unusual two‐step reversible structural phase transitions which consist of a ferroelastic phase transition and a special structural phase transition without symmetry breaking in a simple clathrate of 18‐Crown‐6 phosphofluoric acid monohydrate, (1). The further molecular dynamic by variable temperature X‐ray Single crystal diffraction and Powder X‐ray diffractions were disclosed that it was driven by two distinct rotation motions namely compass‐like rotation and windlass‐like rotation. Two pairs of distinct reversible step‐like dielectric anomalies with electrical tristabilities among high, middle and low dielectric states at 278/281 K and 292/296 K in heating/cooling runs suggest that it can be a potential switchable dielectric molecular material within a narrow temperaturespan (15 K). The DSC curves show analogous heat anomalies at the same temperatures and further confirm the reversible phase transition behaviors.