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.