Synthesis and thermoelectric property of Ca and In-doped n-type Bi$_{85}$Sb$_{15}$ alloy

In the present work we investigated the thermo-electric properties of undoped Bi$_{85}$Sb$_{15}$ and different Ca-doped Bi$_{85}$Sb$_{15}$Ca$_{x}$ (x$=$0.5, 2, and 5) and In-doped Bi$_{85}$Sb$_{15}$In$_{\mathrm{x}} $(x$=$0.5, 2) alloys synthesized via arc-melting first and followed by ball milling and hot pressing. Effect of different Ca and In doping levels on transport properties of Bi$_{85}$Sb$_{15}$ alloys has been investigated. It is found that thermal conductivity decreases with increasing Ca and decreasing In. Electrical transport measurements show that power factor increases with doping level of Ca up to Bi$_{85}$Sb$_{15}$Ca$_{2}$ and then decreases yielding the maximum power factor of 3.8 $\times$ 10$^{-3}$ Wm$^{-1}$K$^{-2}$ and zT of 0.39 at room temperature for Bi$_{85}$Sb$_{15}$Ca$_{2}$. For indium doping, power factor decreases with doping level from 0.5 to 2, yielding the maximum zT value of 0.37 at room temperature for Bi$_{85}$Sb$_{15}$In$_{0.5}$. In this work, calcium doping in Bi$_{85}$Sb$_{15}$ alloy is found to yield better thermoelectric property than indium doping.