Synthesis of Co-doped β-FeSi2/Si composites through eutectoid decomposition and its thermoelectric properties

Abstract

We attempted to synthesize composites of Co-doped β-FeSi2 thermoelectric material with fine Si dispersion from α phase composition of Fe2Si5. We annealed the sintered bodies through eutectoid decomposition of high-temperature α phase to low-temperature semiconducting β phase in Fe–Si system. As a result, we obtained micro to nanoscale differences in Si distribution caused by the different annealing times and temperatures. Sizes of dispersed Si particles ranged between 100 and 300 nm. Seebeck coefficient of Co-doped β-FeSi2 with Si dispersion is higher than that of the conventional singular phase Co-doped β-FeSi2. This value overpowers the increase in electrical resistivity and thermal conductivity, thus elevating the dimensionless figure of merit, ZT from approximately 0.05–0.085. Furthermore, thermal conductivity of Co-doped β-FeSi2/Si composite annealed at 800 °C for 4 h was lower than calculated value from the rule of mixture where dispersed structure was not considered in the calculation. This proves that Si dispersions help suppress thermal conductivity.