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 ± 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.
@article{arxiv.1405.1527,
title = {First-order structural transition in the multiferroic perovskite-like formate [(CH3)2NH2][Mn(HCOO)3]},
author = {M. Sanchez-Andujar and L. C. Gomez-Aguirre and B. Pato Doldan and S. Yanez-Vilar and R. Artiaga and A. L. Llamas-Saiz and R. S. Manna and F. Schnelle and M. Lang and F. Ritter and A. A. Haghighirad and M. A. Senaris-Rodriguez},
journal= {arXiv preprint arXiv:1405.1527},
year = {2014}
}