Enhancement of Thermoelectric Performance in n-type PbTe$_{1-y}$Se$_{y}$ by Cr Doping

Lead telluride and its alloys have been extensively studied for medium temperature thermoelectric applications. However, little emphasis has been given to improve the figure-of-merit (\textit{ZT}) near room temperature. In this investigation, we report a systematic study of Cr doping in PbTe$_{1-y}$Se$_{y}$ with $y =$ 0, 0.25, 0.5, 0.75, 0.85, and 1. We found the peak \textit{ZT} temperature increased with increasing concentration of Se. A highest \textit{ZT} of $\sim$ 0.6 at room temperature in Te-rich Cr$_{0.015}$Pb$_{0.985}$Te$_{0.75}$Se$_{0.25}$ was obtained due to a lowered thermal conductivity and enhanced power factor resulted from high Seebeck coefficient of about -220 $\mu$V K$^{-1\, }$and high Hall mobility $\sim$ 1120 cm$^{2}$ V$^{-1\, }$s$^{-1}$ at room temperature. A room temperature \textit{ZT} of $\sim$ 0.5 and peak \textit{ZT} of $\sim$ 1 at about 573 K to 673 K is shown by Se-rich sample Cr$_{0.01}$Pb$_{0.99}$Te$_{0.25}$Se$_{0.75}$. This improvement of the room temperature \textit{ZT} improved the average \textit{ZT} over a wide temperature range and could potentially lead to a single leg efficiency of thermoelectric conversion for Te-rich Cr$_{0.015}$Pb$_{0.985}$Te$_{0.75}$Se$_{0.25}$ up to $\sim$ 11 {\%} and Se-rich Cr$_{0.01}$Pb$_{0.99}$Te$_{0.25}$Se$_{0.75}$ up to $\sim$ 13 {\%} with cold side and hot side temperature at 300 K and 873 K, respectively, if matched with appropriate p-type legs.