First-order structural transition in the multiferroic perovskite-like formate [(CH3)2NH2][Mn(HCOO)3]

TL;DR

This study reveals a first-order structural phase transition in the multiferroic perovskite-like formate [(CH3)2NH2][Mn(HCOO)3] at around 187 K, involving symmetry change, twinning, and a significant pressure dependence, with implications for tuning its properties.

Contribution

It provides detailed structural analysis of the phase transition in [(CH3)2NH2][Mn(HCOO)3], including symmetry change and pressure dependence, advancing understanding of its multiferroic behavior.

Findings

Structural phase transition at ~187 K involving symmetry change from R-3c to Cc.

Twinning and discontinuous changes in unit cell parameters observed.

Large pressure dependence of transition temperature (dTt/dP ≈ 4.6 K/kbar).

Abstract

In this work we explore the overall structural behaviour of the [(CH3)2NH2][Mn(HCOO)3] multiferroic compound across the temperature range where its ferroelectric transition takes place by means of calorimetry, thermal expansion measurements and variable temperature powder and single crystal X-ray diffraction. The results clearly proof the presence of structural phase transition at Tt ~187 K (temperature at which the dielectric transition occurs) that involves a symmetry change from R-3c to Cc, twinning of the crystals, a discontinuous variation of the unit cell parameters and unit cell volume, and a sharp first-order-like anomaly in the thermal expansion. In addition, the calorimetric results show a 3-fold order-disorder transition. The calculated pressure dependence of the transition temperature is rather large (dTt/dP = 4.6 $\pm$ 0.1 K/kbar), so that it should be feasible to shift it to room temperature using adequate thermodynamic conditions, for instance by application of external pressure.