Experimental and computational phase boundary mapping of CoSnTe.

Binary CoSb skutterudite (also known as CoSb) has been extensively studied; however, its mixed-anion counterparts remain largely unexplored in terms of their phase stability and thermoelectric properties. In the search for complex anionic analogs of the binary skutterudite, we begin by investigating the CoSb-CoSnTe pseudo-binary phase diagram. We observe no quaternary skutterudite phases and as such, focus our investigations on the ternary CoSnTe experimental phase boundary mapping, transport measurements, and first-principles calculations. Phase boundary mapping using traditional bulk syntheses reveals that the CoSnTe exhibits electronic properties ranging from a degenerate p-type behavior to an intrinsic behavior. Under Sn-rich conditions, Hall measurements indicate degenerate p-type carrier concentrations and high hole mobility. The acceptor defect Sn, and donor defects Te and Co are the predominant defects and rationally correspond to regions of high Sn, Te, and Co, respectively. Consideration of the defect energetics indicates that p-type extrinsic doping is plausible; however, Sn is likely a killer defect that limits n-type dopability. We find that the hole carrier concentration in CoSnTe can be further optimized by extrinsic p-type doping under Sn-rich growth conditions.