The effect of elemental substitution on the electronic properties of Ru₂Ge₃

The effect of chemical substitution on the electrical resistivity and Seebeck coefficients of Ru₂Ge₃ is reported, with a particular emphasis on enhancing the properties relevant to thermoelectric behaviour. The properties of Ru₂Ge₃ itself are shown to be strongly dependent on quenching temperature. The effects of metal doping for Ru and metalloid substitution (Sn and Si) for Ge are reported. It is shown that doping of both ruthenium and germanium sites is required to reduce the high resistivity of Ru₂Ge₃ (∼280 mΩ cm at 300 K) to a value of 1.5 mΩ cm, for Ru_1.85Mn_0.15Ge_2.4Sn_0.6 while maintaining high Seebeck coefficients. This latter composition has the highest thermoelectric figure of merit observed in this system: ZT_{300 K} = 1 × 10^-2. Unfortunately this value is too small to be competitive with existing materials.