New n-type silicide thermoelectric material with high oxidation resistance

In order to achieve waste heat recovery using thermoelectric systems, thermoelectric materials showing high conversion efficiency over wide temperature range and high resistance against oxidation are indispensable. A silicide material with good n-type thermoelectric properties and oxidation resistance has been discovered. The composition and crystal structure of the silicide are found out Mn₃Si₄Al₂ (abbreviated as 342 phase) and hexagonal CrSi₂ structure, respectively. Element substitution of Mn with 3d transition metals is succeeded. Enhancement of Seebeck coefficient is observed in a Cr-substituted sample. The maximum dimensionless thermoelectric figure of merit ZT is 0.3 at 573 K in air for the Mn_2.7Cr_0.3Si₄Al₂ sample. Electrical resistivity of the Mn₃Si₄Al₂ bulk sample holds constant value for 48 h at 873 K in air. This is due to formation of oxide passive layer on the surface of the bulk sample. The 342 phase is a promising n-type material with a good oxidation resistance in the middle temperature range of 500-800 K.