Ferroelastic phase transition in [(C₂H₅)₄N][(CH₃)₄N]MnBr₄

ABSTRACT

Crystal growth, DSC, X-ray structural studies, optical observation and dielectric studies for a new hybrid organic–inorganic [(C₂H₅)₄N][(CH₃)₄N]MnBr₄ crystal are presented. The studies revealed reversible first-order phase transition of a ferroelastic type at 484/482 K on a heating and cooling run, respectively. Unusual feature of this transition is reduction of symmetry on heating run. At room temperature phase the crystal is tetragonal with the space group $P\overline{4}{2}_{1}m$ and above the phase transition temperature it is orthorhombic with the space group $P{2}_1{2}_{1}2$. The symmetry change at the transition fulfills the reverse group–subgroup relation. Above the phase transition, the ferroelastic domain structure consistent with Aizu's species $\overline{4}2mF222$ was revealed by polarized microscopy observation. The phase transition exhibiting such features has not been presented so far. Dielectric studies revealed a significant increase of losses connected with conductivity. The temperature dependence of conductivity and conductivity relaxation time fulfill the Arrhenius relation and activation energies are estimated.

KEYWORDS:

• Phase transition
• dielectric properties
• domain structure
• ferroelasticity

Disclosure statement

No potential conflict of interest was reported by the authors.