SUPERCONDUCTIVITY IN THE PBTE-SNTE-GETE SYSTEM WITH IN AND TL QUASI-LOCAL IMPURITY STATES

Superconducting (SC) materials based on A(IV)B(VI) solid solutions wit h deep impurity resonant states of group III elements (In, Tl) was inv estigated. It was shown that the necessary conditions for the appearan ce of SC with T-c>lK are: i) the Fermi level is placed in an impurity band; ii) impurity states are situated near the additional valence ban d extremum with the high density of states (the Sigma- extremum in mat erials based on PbTe:Tl and the Sigma- or Delta- extremum in materials based on SnTe:In). On the other hand, in the case of (Sn1-zGez)(1-x)I nxTe the changes of the band structure and the impurity band position may be caused by a structural phase transition observed by resistivity , Hall-effect, X-ray and magnetization measurements.