Vacancy induced anomalies in the electrical transport properties of Ag-doped Zn1−xCdxSb (x = 0.375) solid solutions

Zinc antimonide (ZnSb) and its solid solution with CdSb are well-known p-type thermoelectric materials. Electrical transport properties of doped ZnSb exhibit certain anomalies: (a) non-monotonic changes in the electrical properties with temperature and (b) occurrence of a reversible hysteresis loop in electrical transport data when thermally cycled. The objective of this study was to investigate the underlying cause of these behaviors. Ag-doped compositions of (Zn0.625Cd0.375)1−δAgδSb (δ = 0, 0.02, and 0.04) solid solutions have been prepared by melt-synthesis—rapid compaction—annealing process. Measurement of the electrical conductivity ( σ), Seebeck coefficient ( S), and Hall coefficient ( R H) (room temperature to 673 K) displayed the characteristic hysteresis behavior on thermal cycling along with the unusual rise in the charge carrier concentration (n) around 500 K. Aside from that, it was found that cooling rates dramatically influence room temperature properties. Analysis of synchrotron-based x-ray diffraction data by Rietveld refinement indicates that Ag-doping results in the formation of Zn vacancies [Vzn]. Also, a sharp drop in the concentration of Zn vacancies, [Vzn] around 550 K was observed and could be correlated with the changes in n values. This correlation between changes in [Vzn] and n has been used to explain the observed electrical anomalies, which are a consequence of the repeated annihilation and creation of Zn vacancies with temperature changes.