Pressure-induced phase transition on K2MoO4: A Raman scattering study and ab initio calculations

This work reports high pressure Raman scattering results on dipotassium molybdate (K2MoO4). The effects of hydrostatic pressure on the vibrational properties of K2MoO4 has been investigated in the pressure range from 0.5 to 7.3 GPa. This study also indicates that K2MoO4 crystals exhibit a pressure-induced first-order phase transition at about 2.2 GPa from monoclinic to an unknown symmetry. Calculaions based on density-functional theory (DFT) unveiled the structural changes undergone by the K2MoO4 system under hydrostatic pressure. The phase transition is connected with the increase of the polyhedral KO6 distortion due to an increased anionic interaction as volume decrease, therefore leading to tiltings and/or rotations of the MoO4 tetrahedra. The consequence of such tiltings and/or rotations of the MoO4 tetrahedra is to increase the disorder of these units. The high-pressure phase transforms directly into the ambient-pressure phase as pressure is released.