Designing vacancy-filled Heusler thermoelectric semiconductors by the Slater-Pauling rule

Heusler alloys with six valence electrons per atom on average are Slater-Pauling semiconductors. The half-Heusler semiconductor exhibits excellent thermoelectric properties due to its specific electronic band structure. In this work, we report on the design and discovery of HfRu1+xSb-based semiconductors using the Slater-Pauling rule. According to the Slater-Pauling rule, the composition HfRu1.5Sb with 21 valence electrons is a stable semiconductor, agreeing well with our theoretical calculation. Experiments reveal that the HfRu1.6Sb sample is nearly an intrinsic semiconductor, which deviates slightly from the Slater-Pauling rule and theoretical calculation. Meanwhile, both p-type (x < 0.6) and n-type (x > 0.6) conductions can be realized in the HfRu1+xSb samples by adjusting the Ru content, and the thermoelectric properties of the HfRu1+xSb samples can be further improved by isoelectronic alloying on the Hf site with Ti. The dimensionless thermoelectric figure of merit zT of p-type HfRu1.4Sb semiconductor is ∼0.37 at 973 K, and the Ti0.9Hf0.1Ru1.4Sb sample reaches a zT value about 0.50 at 973 K, achieving an increase of 30%. Our work shows that more vacancy-filled Heusler semiconductors with tunable and promising thermoelectric properties could be designed based on the Slater-Pauling rule.