Electronic behaviour of liquid Se0.5Te0.5 doped with monovalent elements

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Abstract
The electrical conductivity s' and thermopower S have been measured in Mx(Se0.5Te0.5)1-x alloys with doping elements M=Tl, Ag, Cu and Na with x' indicates that electronic transport shifts at x<0.02 from the valence band of Se0.5Te0.5 to an acceptor band which grows with increasing x. The conductivity of the states in the band increases exponentially with T, and this is accounted for by thermal dissociation of the acceptor ions from clusters with the positive ions which form at low T. Analysis of the dependence of S on composition supports the conclusion that the acceptor ions are diatomic molecular ions formed by the doping element and the chalcogen, and the positive ions are threefold-bonded (D+) chalcogen ions. For Cu alloys, there is evidence that most of the copper dopant atoms are in the bivalent state at low T.