The crystal structures of the high-temperature phases of Ag4Mn3O8

Two endothermic, reversible structural phase transitions of first order have been observed in Ag4Mn3O8 by means of in-situ powder diffraction and by differential scanning calorimetry. At a temperature of T = 477 K, Ag4Mn3O8 undergoes a structural phase transition from the room temperature phase in space group P3(1)21 to a phase in space group R32, and at T = 689 K a second phase transition to a structure in space group P4(3)32 occurs. Whilst the Mn3O8 framework does not change significantly upon heating, rearrangements of the silver atoms, located in the cavities of the framework, were found to be the driving force behind the transitions. The structural chances with increasing temperature proceed along a path of minimal group-supergroup relations between the respective space groups.