High pressure Raman scattering and X-ray diffraction studies of MgNb2O6

High pressure X-ray diffraction and Raman scattering studies have been carried out on magnesium niobate (MgNb2O6) in a diamond anvil cell (DAC) at room temperature up to 40 GPa. A pressure-induced phase transition was observed at pressures above 10 GPa accompanied by a softening of the internal ν9 (B3g) modes. Raman scattering results reveal that the distortion of the NbO6 octahedra decreases under high pressure. According to the X-ray diffraction data, the high pressure phase can be indexed with a monoclinic unit cell. The initial orthorhombic phase changes to a monoclinic phase possibly due to the rotation of the NbO6 octahedra, similar to some perovskite ABO3 structures.