Pressure effect on structure transition and optical anisotropy in MoO3

We investigated the phase transition and anisotropic optical property of MoO3 under pressure by optical spectroscopy. An α-MoO3 to MoO3-II transition and another MoO3-II to MoO3-III transition were observed at 11 and at 27 GPa, respectively. Accompanied by the structural transition, its optical anisotropy also changes with pressure. While maintaining the similar angle-resolved intensity patterns, the polarization angle with the maximum intensity of the Mo–O2–Mo symmetric stretching mode moves from 90° to 105° then back to 90° with pressure. The result is helpful to understand the mechanism of the pressure-induced phase transition and tune the anisotropic optical properties of MoO3.