Thermoelectric properties of n-type Mn3−xCrxSi4Al2 in air

A silicide material with a good n-type thermoelectric property has been discovered. This silicide possesses a composition of Mn3−xCrxSi4Al2 (0 ≤ x ≤ 0.7) and hexagonal CrSi2 structure. The a- and c-cell parameters decrease with increasing the amount of Cr substitution. The absolute values of Seebeck coefficient and electrical resistivity increase by Cr substitution up to 573 K because of reduction of carrier density. The dimensionless thermoelectric figure of merit ZT reaches 0.21 at 773 K for a non Cr substituted sample at the Mn site and 0.30 at 573 K for a Cr substituted one with x = 0.3. Since oxide passive layer is formed around the surface, electrical resistivity measured at 873 K is constant for 2 days in air, which indicates good oxidation resistance in air of this material. The Mn3−xCrxSi4Al2 is a promising n-type material with a good oxidation resistance in the middle temperature range. A thermoelectric module consisting of 64 pairs of legs has been fabricated using MnSi1.7 and non Cr substituted Mn3Si4Al2 devices as p- and n-type legs, respectively. Output power reaches 9.4 W, which corresponds to 2.3 kW/m2 of power density against surface area of the substrate, for a heat source temperature of 873 K in air.