Electrical properties of some (1,1,1) intermetallic compounds

Many intermetallic compounds form with a gap in their density of states at the Fermi level, giving rise to relatively large Seebeck coefficients, on the order of -150 to -300 mu V/deg. at room temperature. Consequently, when combined with reasonable carrier mobilities in the range of 30 to 50 cm(2)/V-s, 'half-Heusler' compounds, such as MNiSn where M = (Ti, Zr, Hf), become attractive candidates for intermediate temperature (300 degrees C to 600 degrees C) thermoelectric applications. Samples of TiNiSn were prepared by are melting and homogenized by various heat treatments. The temperature dependence of the electrical resistivity, Seebeck coefficient, and thermal diffusivity of these samples was characterized between 22 degrees C and 900 degrees C. The electrical resistivity and thermopower both decrease with increasing temperature, consistent with semiconducting behavior. The electrical power factor, defined as S-2/rho where S is the Seebeck coefficient and rho is the resistivity, appears quite sensitive to the degree of homogenization in the microstructure and values in excess of 25 mu W/cm-degrees C-2 were observed in nearly single phase alloys within the 300 to 600 degrees C temperature range. A brief survey of other selected ternary intermetallic compounds is also presented. (C) 1999 Kluwer Academic Publishers.