Improving p-type thermoelectric performance of Mg2(Ge,Sn) compounds via solid solution and Ag doping

► Mg2(Ge,Sn) solid solutions were well prepared by melting in evacuated Ta tubes. ► We observed an n- to p-type crossover in two samples at elevated temperatures. ► The thermal conductivities of Mg2Ge1−xSnx fit well with Ioffe's theory. ► Ag is an effective acceptor in solid solution with a solution limit of ∼2%. ► A maximum ZT ∼0.38 was attained.