Structure, Stoichiometry, and Properties of the Chimney-Ladder Phases Ru2Ge3+x (0<x<1)

The preparation and physical characterization of non-stoichiometric Ru2Ge3+x (0≤x≤1) are reported for the first time. The defect TiSi2-type chimney-ladder structure is maintained for the full stoichiometry range. The resistivity of Ru2Ge3+x increases systematically with x from 300 mΩ cm, x=0 –3 Ω cm, x=1 at 300 K. The temperature dependence is consistent with a variable range-hopping mechanism for x≥0.6. The Seebeck coefficients of samples do not evolve simply with x. A low thermal conductivity (κ300 K=0.03 W/K cm) suggests that Ru2Ge3 has some of the properties of a phonon-glass–electron-crystal. The low value of the thermoelectric figure of merit ZT=3.2×10−3 (T=300 K) calculated for Ru2Ge3 is due primarily to a low conductivity. [Copyright &y& Elsevier]