Growth of centimeter-sized [(CH3)2NH2][Mn(HCOO)3] hybrid formate perovskite single crystals and Raman evidence of pressure-induced phase transitions

Abstract

[(CH₃)₂NH₂][Mn(HCOO)₃], an organic–inorganic perovskite-like hybrid multiferroic, shows promising aspirations for the next generation magnetic storage devices, light-weight chips, optical devices, etc. However, the growth of centimeter-sized large single crystals of [(CH₃)₂NH₂][Mn(HCOO)₃] remains a big challenge. Herein, we report a facile, environmentally friendly approach to grow [(CH₃)₂NH₂][Mn(HCOO)₃] single crystals whose size could be up to 10 × 9.61 × 3.6 mm, the biggest one ever reported to date. In addition, high-pressure Raman spectra of the material exhibited the existence of three high-pressure polymorphs at 2.1, 4.1, and 6.7 GPa. The high-pressure phase transitions are associated with highly distorted frameworks, and the phase under a pressure larger than 6.7 GPa induces large structural changes in the hydrogen bond-related interactions, which is different from the highly ordered low-temperature monoclinic ferroelectric phase (Cc) observed at ambient pressure. Our studies may shed light on the phase transition mechanisms of the multiferroic metal–organic framework [(CH₃)₂NH₂][Mn(HCOO)₃] under high pressures.