Raman Investigation of the Low Temperature Phase Transitions in Monoclinic TlReO4

The Raman spectrum of monoclinic TlReO₄ is presented together with a factor group analysis and assignment of the bands. The phase transitions of monoclinic TlReO₄ is investigated below room temperature, and two phase transitions were identified between room temperature and 90 K. The room temperature monoclinic phase was converted to the orthorhombic phase at 170 K upon cooling, and to the tetragonal phase at 150 K. Upon heating back to room temperature the tetragonal phase persisted until the orthorhombic phase could be identified at 210 K and 220 K. From 230 K to room temperature the monoclinic phase could again be observed.