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

We present structural studies of V_1-xCrₓO₂ (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 M₁ symmetry between 4 and 12 GPa. Above 12 GPa, the monoclinic M₁ symmetry changes to isostructural Mₓ phase (space group P2₁/c) with a significant anisotropy in lattice compression of the b-c plane of the M₁ phase. This behavior can be reconciled invoking the pressure-induced charge delocalization.