The electrical resistivity (semiconductor–metal transition), the thermoelectric power, and the magnetic susceptibility of well‐characterized VO2 monocrystals and powdered samples in the range of homogeneity were measured. The physical properties gave no hint of an extension of the range of homogeneity towards oxygen excess. An oxygen deficit (VO1.994) strongly influence the semiconductive properties of VO2 below the phase transition temperature, but hardly influences the metallic properties above the transition temperature. This behaviour may be explained by the formation of vanadium interstitial atoms and a rise in the concentration of mobile electrons connected with it. These results explain discrepancies in the data of the physical properties in literature, and show how the properties of VO2 can be purposefully changed.

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Vanadium dioxide is prepared by sintering, chemical transport, and deposition in an open system and the optimal preparation conditions are given. The products, prepared by these methods, are characterized by crystallographical and chemical analysis. The upper and lower phase boundary of vanadium dioxide are determined to VO2.002±0.002 and VO1.995±0.002, respectively.

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