Compression effect on structure of the Li-stabilized high-temperature phase of Mn3(VO4)2 with composition Li0.2Mn2.9(VO4)2 - Raman spectroscopic and X-ray diffraction investigations

Abstract

Tetragonal Mn3(VO4)2 is a metastable high temperature phase of Mn3(VO4)2 showing unusual coordination of Mn atoms. A nominal Li-substitution helps to stabilize the tetragonal modification. We report room temperature compression of Li-stabilized high-temperature tetragonal phase of Mn3(VO4)2 with composition Li0.2Mn2.9(VO4)2 studied by in-situ Raman spectroscopy and synchrotron X-ray diffraction up to pressures of 20 and 26.5 GPa respectively. Raman spectroscopy suggests onset of a structural phase transition at around 10 GPa which completes above 13 GPa. X-ray diffraction also suggested a first order structural transition above 10 GPa, with a coexistence range of two phases up to 13 GPa. High pressure phase is found to be different from the known thermodynamically stable orthorhombic structure of Mn3(VO4)2. The equation of state data of the ambient tetragonal phase has been obtained. Anisotropic compression is observed with the c-axis being more compressible than a-axis. Using experimental bulk modulus, the mode Grüneisen parameters for the observed Raman frequencies for the ambient phase have been obtained. On pressure release, the high pressure phase could be retrieved.