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

Abstract

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 μV/deg. at room temperature. Consequently, when combined with reasonable carrier mobilities in the range of 30 to 50 cm2/V-s, ‘half-Heusler’ compounds, such as MNiSn where M = (Ti, Zr, Hf), become attractive candidates for intermediate temperature (300°C to 600°C) thermoelectric applications. Samples of TiNiSn were prepared by arc 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°C and 900°C. The electrical resistivity and thermopower both decrease with increasing temperature, consistent with semiconducting behavior. The electrical power factor, defined as S2/ρ where S is the Seebeck coefficient and ρ is the resistivity, appears quite sensitive to the degree of homogenization in the microstructure and values in excess of 25 μW/cm-°C2 were observed in nearly single phase alloys within the 300 to 600°C temperature range. A brief survey of other selected ternary intermetallic compounds is also presented.