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 7.3GPa. This study also indicates that K2MoO4 crystals exhibit a pressure-induced first-order phase transition at about 2.2GPa 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. Dipotassium molybdate (K2MoO4) belongs to the class of single molybdates and tungstates with a general composition of the A2MO4 (A=Li, Na, K, Rb, Cs; Μ=Mo, W). At room temperature and ambient pressure, the crystal of K2MoO4 is monoclinic and it belongs to the C2/m (C2h3) space group. This material is attracting a considerable attention due to its interesting structural and thermodynamic properties. This work reports a high pressure study on this system. [Display omitted] ► We reports high pressure Raman scattering results on dipotassium molybdate. ► Our study indicates a pressure-induced first-order phase transition at around 2.16GPa. ► DFT calculations indicate that phase transition is connected with the increase of KO6 distortion. ► Tiltings and/or rotations of the MoO4 tetrahedra are related to increased disorder.