Raman-scattering studies of pressure-induced phase transitions in perovskite-like acetamidninium manganese formate

We report high-pressure Raman scattering studies of acetamidninium manganese formate, which show evidence for two pressure-induced phase transitions between 0.7 and 1.4GPa and above 5.3GPa. The first transition is related to distortion of the manganese formate framework whereas the second one affects significantly the structure of the acetamidinium cation. Significant narrowing of the lattice bands suggests that the intermediate and high-pressure phases are ordered. High-pressure experiments also indicate different structures of the intermediate phases observed upon compression and decompression. However, release of pressure to ambient value leads to recovery of the initial ambient-pressure phase.