Vodorez O. Peculiarities of concentration dependences of properties in solid solutions based on IV-VI semiconductor compounds

The thesis is devoted to studying the dependences of structure, mechanical and thermoelectric properties on the composition of undoped solid solutions based on IV-VI compounds with a view to revealing peculiarities associated with the interactions of impurity atoms among themselves, with host crystal atoms and non-stoichiometry defects. For the first time, in the PbTe-PbSe, PbTe-Bi2Te3 and PbTe-CuInTe2 systems, concentration anomalies of structural and thermoelectric properties at impurity concentrations below ~ 1.0 mol.% were observed and attributed to the existence of percolation-type transitions from dilute to concentrated solid solutions. A sharp increase in configurational entropy under the introduction of the first portions of impurity leads to complex mechanisms of the defect formation in the dilute solid solution region; charge carrier mobility and the lattice component of thermal conductivity decrease drastically, and the initially neutral compounds Bi2Te3 and CuInTe2 become electrically active. It is established that in concentrated PbTe-PbSe and PbTe-Bi2Te3 solid solutions, isotherms of properties exhibit an oscillatory behavior, which is an evidence for the realization of intermediary states in the system with different types of space correlations. In the PbTe-Bi2Te3 and PbTe-CuInTe2 systems, concentration anomalies are observed, whose presence is attributed to the reaching of the "complex formation threshold". It is shown that the existence of a deviation from stoichiometry significantly affects the behavior of the dependences of properties on composition in dilute solid solution region. The non-monotonic behavior of the concentration dependences of properties, the influence of non-stoichiometry defects on the character of change in properties under doping should be taken into account when developing new thermoelectric materials and predicting their characteristics.