Enhancement of the thermoelectric performance of half-metallic full-Heusler Mn₂VAl alloys via antisite defect engineering and Si partial substitution

A half-metallic full-Heusler Mn₂VAl alloy is a potential p-type thermoelectric material that can directly generate electricity from waste heat via the Seebeck effect. For practical use, the Seebeck coefficient S of Mn₂VAl should be increased while maintaining a high electrical conductivity σ from its half-metallic character. Herein, we achieved this objective through antisite defect engineering. Theoretically, it was predicted that the S was maximized by regulating partial density of states of majority-spin sp-electrons through the control of the fraction of antisite defect, f_AD, between V and Al atoms in Mn₂VAl. Experimentally, a significant increase in S and a slight decrease in σ were observed for an Mn₂VAl sample with an optimal f_AD = 33%, enhancing the thermoelectric power factor PF by 2.7 times from an Mn₂VAl sample with f_AD = 14%. Furthermore, we combined the antisite defect engineering with a partial substitution method. An Mn₂V(Al_0.96Si_0.04) sample with f_AD = 33% exhibited the highest PF = 4.5 × 10⁻⁴ W·m⁻¹·K⁻² at 767 K among the samples. The maximum dimensionless figure-of-merit zT of the Mn₂V(Al_0.96Si_0.04) sample with f_AD = 33% was measured to be 3.4 × 10⁻² at 767 K, which is the highest among the p-type half-metallic full-Heusler alloys.