Electronic properties as a function of Ag/Sb ratio in Ag_1-y Pb₁₈Sb_1+z Te₂₀ compounds

In this study efforts have been made to optimize the electronic properties such as the electrical conductivity and Seebeck coefficient of Ag_{1- y} Pb₁₈Sb_{1+ z} Te₂₀ (lead-antimony-silver-tellurium, LAST-18) compounds by systematically varying the Ag and Sb compositions with constant Pb/Te ratio. It was found that increasing the content of Sb relative to Ag raised the charge carrier density (n) and thereby the electrical conductivity and power factor. The results indicate that, for deficient Ag, the excess trivalent Sb atoms occupy divalent Pb sites in the unit cell, increasing the value of n in the system. It was established that the Seebeck coefficient decreases with increasing n, indicating a dominant acoustic phonon scattering mechanism in the current alloys. The results demonstrate that the interaction between Ag and Sb atoms plays a major role in determining the electronic properties in the current Ag_1-y Pb₁₈Sb_1+z Te₂₀ compounds.