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A high-pressure Raman study of microcrystalline tungsten oxide was performed in the 0.1 MPa-30 GPa pressure range under hydrostatic and non-hydrostatic conditions. Two phase transitions are evidenced; they take place below 0.1 GPa and at about 22 GPa and are of first order. Two spectral anomalies are observed at about 3 and 10 GPa; they may be related to diffuse weak structural transitions. The number of observed Raman bands remains practically unchanged in the 0.1-30 GPa range and thus the symmetry changes are likely to be small. Surprisingly, the non-hydrostatic conditions do not induce inhomogeneous band broadening and do not modify the transition sequence observed in hydrostatic conditions. The compressibilities of the different observed phases are estimated from spectral data and discussed within Hazen's polyhedral approach.

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