A high-pressure single-crystal X-ray diffraction study of V₃O₅ including the phase transition at 6.2 GPa

The unit-cell parameters of the mixed-valence oxide V₃O₅ have been studied as functions of pressure from 0.3 up to 7.5 GPa in a single-crystal experiment involving measurements at 21 different pressure values. A diamond-anvil high-pressure (h.p.) cell of new construction [Malinowski (1987). Submitted to J. Appl. Cryst.] mounted on a four-circle X-ray diffractometer was used. At P_t = 6.25(9) GPa a phase transition was observed at room temperature. This is analogous to the semiconductor-metal transition observed at T_t = 428 K and normal pressure, which implies a change in the ordering of the metal-atom valencies. The linear Eulerian strain tensor for the transition has been calculated. The bulk modulus K has been determined for the low-pressure (l.p.) as well as for the h.p. phase: K^l.p.(0.3-5.5 GPa) = 269(3), K^h.p.(6.3-7.5 GPa) = 175(11) GPa. Certain anomalies in the cell-parameter values in a small pressure interval around the phase transition indicate a preparation in the crystal structure for the transition in both the l.p. and the h.p. phase.