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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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The electrical, thermoelectric, magnetic, and crystallographic properties of Ga-doped VO, single crystals V1-,Ga,O, (0 5 x 5 0.013) are investigated. By Ga-doping the transition temperature of the semiconductor-metal transition of VO, is elevated and the resistivity discontinuity is little increased. The T-x-phase diagram containing the phases M1, T, M 2 , and R is indicated. The phase transition T-M2 is a semiconductor-semiconductor transition with discontinuities in the properties investigated. By Ga-doping portions of anisotropic p-conduction arise. Without falsifying by paramagnetic ions the magnetism of linear Heisenberg chains with antiferromagnahic interaction may be seen in the M2 phase. Es werden die elektrischen, thermoelektrischen, magnetischen und kristallographischen Eigenschaften von Ga-dotierten V0,-Einkristallen V1 -zGa,O, (0 5 z 5 0,013) untersucht. Durch die Ga-Dotierung wird die Ubergangstemperatur fiir den Ralbleiter-Metall-Ubergang von VO, bei geringer VergroBerung des Widerstandssprunges erhoht. Das T-x-Phasendiagramm mit den Phasen M1, T, M2 und R wird angegeben. Der Phaseniibergang T-M2 ist ein Halbleiter-Halbleiter-U$erg&ng mit Diskontinuitiiten in &n untersuchten Eigenschaften. Durch die Ga-Dotierung entstehen anisotrope p-Iaitungsanteile. In der MZ-Phase tritt unverfiilscht durch paramagnetische Ionen der Magnetismus h e a r e r Heisenbergketten mit antiferromagnetischer Wechselwirkung auf.1. such which lower the transition temperature, e.g. MOO, 13.41, WO, 151, NbO, [6 to 91, and 2. such which raise the transition temperahre. I n this group the Cr-doped VO, has been investigated as a model substance to a great extent [lo to 131. More recent papers are presented concerning the systems V1-,Fe,O, [ 14, 151, V~-,A1,0, [16, 171, V1-,GeZO, [18] etc.

For monocrystalline V1‐xMexO2‐y samples (Me = Ga, Al, Fe) the effect of nonstoichiometry (oxygen deficiency) on the electrical, magnetic, and structural properties of Me3±‐doped vanadium dioxide is investigated. The influence of acceptor‐like defects caused by the Me3± doping is compensated by donor‐like defects caused by the oxygen deficiency. The nature of the predominant electronic defects (additional electrons or holes) essentially influences the modification behaviour of VO2 (transition temperature, crystallographic distortions, conductivity jump).