Doping-Induced Polymorph and Carrier Polarity Changes in Thermoelectric Ag(Bi,Sb)Se 2 Solid Solution

Silver bismuth diselenide (AgBiSe ) is an n-type thermoelectric material that exhibits a complex structural phase transition from the hexagonal to cubic phase, while silver antimony diselenide (AgSbSe ) is a p-type thermoelectric material that crystallizes in the cubic phase at all temperatures. Here, we investigate the crystal structure and thermoelectric properties of Ag(Bi,Sb)Se solid solution, employing AgBi Sb Se and AgBi Sb Se as representative samples. The carrier polarity of AgBi Sb Se is converted from the n-type to p-type by Pb doping, accompanied by a polymorphic change to the cubic phase. It is difficult to obtain highly conductive p-type hexagonal AgBiSe -based materials, although first-principles calculations predict high-performance thermoelectric properties for these systems. We also demonstrate that cubic AgBi Sb Se undergoes a polymorphic change to the hexagonal phase upon Nb doping. The present study show that polymorphic changes inevitably occurred upon Pb/Nb doping to optimize thermoelectric properties of Ag(Bi,Sb)Se solid solution.