Metal-semiconductor phase transition in vanadium oxides and technical applications

Existing theories for the metal-semiconductor phase transition which are pertinent to this transition in vanadium oxides are reviewed. The best model for interpreting the phase transition in V$sub 2$O$sub 3$ is the model proposed by Aronov and Kudinov, in which the phase transition is attributed to an instability which arises in the subsystem of Frenkel' excitons. Experimental data supporting this point of view are reported. In vanadium dioxide the most probable explanation for the phase transition seems to be an instability of lattice vibrations, but effects due to an electron-electron interaction are also manifested experimentally. The observed metal-semiconductor phase transition in the series V/sub n/O/sub 2n-1/(n=3--9) is not related to a change in magnetic order. Many of the properties in this series, e.g., the magnetic properties, can be understood assuming that the V$sup 3+$ ion is in cleavage planes and that the V$sup 4+$ ion is in rutile blocks between these planes. The metal-semiconductor phase transition in vanadium oxides is used in automation and control applications (in thermistors with a ''critical point'') and can be used in microelectronics and opto-electronics. (AIP)