Efficient Reduction of Carrier Concentration in SnTe: The Case of Gd Doping

Lead-free SnTe with naturally non-stoichiometric vacancies has a limited thermoelectric performance due to a deviated carrier concentration from the optimum. In this paper, we experimentally demonstrated that Gd with + 3 valence state as a novel n-type dopant is an effective solution for reducing carrier concentration in SnTe. A lowest value of 7.6 × 10¹⁸ cm⁻³ has been achieved. Yet with the involvement of Gd doping, the slightly modified band structure requires a further Sn-deficiency compensation to enhance the overall figure of merit zT. As a consequence, in the specific sample Sn_0.91Gd_0.07Te, we successfully achieved a low lattice thermal conductivity of 0.8 W/(m K) due to the high doping level and an improved zT approaching 0.8 at 850 K.