Thermoelectric Properties of Si2Ti-Type Al-(Mn,Cr,Fe)-Si Alloys

To optimize the thermoelectric properties of Si2Ti-type Al32Mn34Si34 (C54-phase), which possesses a large absolute Seebeck coefficient |S| exceeding 300 mu V/K with negative sign, we partially substituted Cr and Fe for Mn, and succeeded in decreasing the number of valence electrons (in the case of Cr) without observing precipitation of secondary phases. A large, positive Seebeck coefficient exceeding 200 mu V/K was observed for Al32Cr (x) Mn34-x Si-34 (1 a parts per thousand currency sign x a parts per thousand currency sign 2.5), which consists almost solely of the C54-phase. The increase of hole concentration caused by Cr substitution for Mn was confirmed by both the reduction in electrical resistivity and the sign reversal of the Seebeck coefficient. The largest ZT-value for positive Seebeck coefficient (p-type behavior) was obtained for Al32Cr2.5Mn31.5Si34, with the resulting ZT-value reaching a magnitude twice as large as the largest ZT-value of the ternary compound Al33Mn34Si33 possessing p-type behavior.