Mesostructure - thermoelectric properties relationships in V Mn1−Si1.74 (x = 0, 0.04) higher manganese silicides prepared by magnesiothermy

Abstract The synthesis of pure pristine and vanadium-doped MnSiγ (γ = 1.74) powder by a relatively fast, ‘low temperature’ and high yield magnesioreduction process is described. The powder obtained by this innovative route is composed of well crystallized grains with sizes ranging from 20 to 500 nm and free from any MnSi precipitates. Mesostructured densified pellets with average grain sizes as small as 550 nm are obtained by spark plasma sintering (SPS). Detailed structural and microstructural characterization of the samples were realized at every stage of the process, highlighting a high concentration of defects such as orientational or spacing anomalies of the Nowotny phase, γ variations within a single grain and dislocations. Accordingly a significant decrease of the lattice thermal conductivity is evidenced in comparison to conventionally synthesized (arc-melting/SPS) samples having similar density and (V/)Mn/Si stoichiometry. The thermoelectric properties of these materials are discussed in regard of their complex microstructure.