Abstract
Nb/Al 2O 3 cermet films were obtained by electron-gun evaporation from two independent sources. Films containing 71 wt.% Nb (particle size about 20 Å) have an activated type of conduction mechanism due to the hopping of the charge carriers between localized states. The activation energy decreases continously from 8.8 x 10 −3 eV (300°K) to 1 x 10 −6 eV (1.9°K), which indicates that the localized states lie close to the Fermi level of the system. These states can be associated with small Nb particles (below the resolution power of the electron microscope—10 Å) in the alumina matrix. Films containing more than 85wt.%Nb (mean particle size 32 Å) have a metallic-type conduction mechanism and show superconductive properties. The transition temperature is reduced to 4.5—5.2°K compared with the Nb bulk value of 9.2°K; this is presumably due to a decrease of the electronic interaction in the surface layer of the Nb particles.
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