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

摘要

In this work we explore the overall structural behaviour of the[(CH3)2NH2][Mn(HCOO)3] multiferroic compound across the temperature range whereits ferroelectric transition takes place by means of calorimetry, thermalexpansion measurements and variable temperature powder and single crystal X-raydiffraction. The results clearly proof the presence of structural phasetransition 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, adiscontinuous variation of the unit cell parameters and unit cell volume, and asharp first-order-like anomaly in the thermal expansion. In addition, thecalorimetric results show a 3-fold order-disorder transition. The calculatedpressure 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 roomtemperature using adequate thermodynamic conditions, for instance byapplication of external pressure.