High pressure effects on the structural and vibrational properties of antiferromagnetic KFe(MoO4)2

The crystal structure of the paraelastic phase of KFe(MoO4)(2) at 360 K was reinvestigated and high pressure Raman scattering experiments were performed on this material. The Studies indicated that this molybdate crystallizes in the P3m1 structure above 312 K. At room temperature the structure is monoclinic and it transforms under pressure into P3m1, P3c1 and low symmetry phases at 0.25, 1.3 and 1.6 GPa, respectively. The phase transitions observed at 0.25 and 1.6 GPa are irreversible whereas the 1.3 GPa transition is reversible. The lattice dynamics calculations performed for the P3m1 phase allowed us to obtain an assignment of observed modes and helped us to obtain insight into the mechanism driving the structural changes occurring in this material. The x-ray study of the highest pressure phase, recovered during the decompression experiment, shows that the crystal structure of this phase is monoclinic or triclinic. When this phase is subjected to heat treatment at 673 K, it either transforms into another phase or decomposes.