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 t he 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 d egrees C) thermoelectric applications. Samples of TiNiSn were prepared by a re melting and homogenized by various heat treatments. The temperature depe ndence of the electrical resistivity, Seebeck coefficient, and thermal diff usivity of these samples was characterized between 22 degrees C and 900 deg rees C. The electrical resistivity and thermopower both decrease with incre asing 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 homogenizatio n 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 tem perature range. A brief survey of other selected ternary intermetallic comp ounds is also presented. (C) 1999 Kluwer Academic Publishers.