Role of milling parameters and impurity on the thermoelectric properties of mechanically alloyed chromium silicide

Mechanical alloying of Cr–Si powders (1:2 molar ratio) was carried out under different milling conditions using stainless steel milling media. In addition to formation of nanocrystalline CrSi2 phase, depending on the milling duration, speed and use of dispersant, X-ray diffraction revealed presence of CrSi phase and EDAX showed iron contamination in varying amounts. The amount of contamination and the secondary phase are found to be linearly proportional to the input impact energy during milling. The nanocrystalline powders are seen to be thermally stable in air up to 900 K. SEM of the hot pressed powders reveal an equiaxed microstructure with grain size depending on the milling duration. Electrical resistivity (ρ), Seebeck coefficient (S) and thermal conductivity (K) were measured up to 700 K. It is seen that the thermoelectric figure of merit (ZT) is high when the amount of secondary phases is minimum. The maximum ZT observed in the samples is ∼0.2 at 600 K which is comparable to other high temperature thermoelectric materials in the temperature range studied.