Anisotropic compression in the high-pressure regime of pure and chromium-doped vanadium dioxide

We present structural studies of V sub(1-x)Cr sub(x)O sub(2) (pure, 0.7%, and 2.5% Cr-doped) compounds at room temperature in a diamond anvil cell for pressures up to 20 GPa using synchrotron x-ray powder diffraction. All the samples studied show a persistence of the monoclinic M sub(1) symmetry between 4 and 12 GPa. Above 12 GPa, the monoclinic M sub(1) symmetry changes to isostructural M sub(x) phase (space group P2 sub(1/c)) with a significant anisotropy in lattice compression of the b-c plane of the M sub(1) phase. This behavior can be reconciled invoking the pressure-induced charge delocalization.