Cobalt and iron doping effects on thermoelectric properties of higher manganese silicides prepared by mechanical milling and pulse discharge sintering

Abstract

Higher manganese silicide (HMS) is promising as one of eco-friendly p-type thermoelectric materials which are useful to power generation system using the waste heat with medium temperature from 600 to 900 K. We investigated about the doping effect of cobalt and iron on thermoelectric properties of the HMS compounds in this study. A combined process of vibration ball milling (VBM) and pulse discharge sintering (PDS) is used for fabricating the HMS compounds. Mn and Si powders milled individually using VBM were mixed with Co or Fe fine powders in argon atmosphere. The powder mixtures were sintered and simultaneously the HMS compounds were synthesized using the PDS process. Syntheses of Co-doped and Fe-doped HMS compounds were confirmed. The lattice parameters of a-axis in (Mn1-xCox)15Si26 compound decreased with Co content (x ≤ 0.01) and held constant within the range of x = 0.01∼0.1, and that in (Mn1-yFey)15Si26 compound decreased linearly with Fe content (y ≤ 0.1). The doping limit of Co in HMS existed around x = 0.01. The thermoelectric performance ZT was decreased with Co content. On the other hand, the maximum ZT of 0.55 was achieved at 773 K by doping Fe with y = 0.005.