High thermoelectric performance of p-type half-Heusler (Hf,Ti)Co(Sb,Sn) solid solutions fabricated by mechanical alloying

Mechanical alloying synthesis was applied on the thermoelectric half-Heusler materials in order to explore the potential of such scalable synthesis method in this family of compounds. (Hf,Ti)Co(Sb,Sn) solid solutions were prepared by mechanical alloying followed by hot pressing and their thermoelectric properties were studied in the temperature range of 300–980 K. After successful synthesis, two different methods were applied to enhance the thermoelectric performance of p-type (Hf,Ti)Co(Sb,Sn) materials: (a) adjustment of the Ti/Hf ratio and (b) fine tuning of carrier concentration by the substitution of Sb with Sn. The isoelectronic substitution of Ti with Hf led to an important reduction in the lattice thermal conductivity and a high ZT of 0.84 at 980 K for Hf_0.6Ti_0.4CoSb_0.8Sn_0.2. The effect of charge carrier concentration was investigated by preparing Hf_0.6Ti_0.4CoSb_1−ySn_y (0.15, 0.17, 0.20, 0.23, 0.25) compounds, using different mechanical alloying durations. The Hf_0.6Ti_0.4CoSb_0.83Sn_0.17 composition, prepared by 4 h ball-milling, reached an impressive ZT ~1.1 at 973 K.