Thermoelectric Power of Tl-Doped PbTe Monocrystal
  Results of the measurements of thermoelectric properties of thin semiconductor microwires of Pb1-xTlxTe (x=0,001-0,02, d=5-100mkm) in the temperature region 4,2-300 K, which were obtained from solution melt by the filling of the quartz capillary with the following crystallization of material are presented. For the samples corresponding to chemical composition with concentration of thallium 0,0025 < x <0,005 double change of the sign of thermoelectric power is observed. In pure samples and samples with thallium concentration more than 1 at% thermoelectric power it is positive in the whole temperature range. Various mechanisms which can lead to observable anomalies, including Kondo-like behavior of a non-magnetic degenerate two-level system are discussed. Obtained experimental results let suppose that the observed anomalies can be interpreted on the basis of model of an impurity with mixed valences. 
E.Zasavitsky