Abstract
Structural phase transitions in metastable rutile-related V(0.92)O(2) synthesized at 10 GPa and 1273 K were studied with single-crystal X-ray diffraction in the temperature range 110-500 K and at pressures up to 9.2 GPa. V(0.92)O(2) starts to decompose at 470 K and atmospheric pressure. When heated to temperatures above about 350 K, the material transforms to an incommensurate phase. The oxygen sublattice is essentially rigid and it is mostly the V atoms that are affected by the modulation. An anharmonic description of the displacement parameters and their corresponding modulation is used for the V atoms to reach satisfactory agreement factors for main and first-order satellite reflections, indicating substantial disorder in the modulated structure. Measurements of electronic transport properties provide evidence that the incommensurate phase is insulating. On compression at room temperature, V(0.92)O(2) reaches the ideal rutile structure at about 5.0 GPa. Both structural and electronic phase transitions are of the first-order character. The results of this work demonstrate that the structural and electronic behaviour of V(0.92)O(2) at extreme conditions is distinctly different from that of stoichiometric VO(2).