Temperature-dependent features of Pb3Mn7O15 crystal structure

The results of X-ray diffraction (XRD) structural investigations of Pb3Mn7O15 crystals carried out for a wide temperature range including the room temperature are presented. It has been observed for the first time that with increasing temperature the Pb3Mn7O15 crystals transform from the orthorhombic (Pnma space group) to the hexagonal (P63/mcm space group) structure. The results of the thermal analysis have revealed two sharp peaks in the temperature dependence correlating with the XRD data. According to the results of the group-theoretical analysis, the Pb3Mn7O15 symmetry transformation can be described as P63/mcm⟹(η,0,0)M2−(12−4)Pnma.