Resistivity and thermopower calculations in half-Heusler Ti1-xScxNiSn alloys from the KKR-CPA method

The Korringa–Kohn–Rostoker method with the coherent potential approximation (KKR-CPA) was applied to calculate electronic structure and transport coefficients in disordered Ti1−xScxNiSn, where semiconductor-to-metal crossovers have recently been observed in resistivity and thermopower experiments (Horyn et al 2004 J. Alloys Compounds 363 10; Romaka et al 2005 J. Alloys Compounds 396 64). We have investigated the effect of chemical disorder on Fermi surface features (i.e. group velocities and life-times related to real and imaginary parts of complex dispersion curves, respectively). This analysis allowed us to shed light on the principal mechanism responsible for the variation of thermoelectric properties. Using the well-known formulae and performing integration over the complex Fermi surface, the residual conductivity and the thermopower slope S/T were estimated. Satisfying agreement between theoretical results and experimental data (measured at 90 and 300 K) has been found. This may indicate that modifications of electronic structure near EF are predominantly responsible for the strong decrease of thermopower in Ti1−xScxNiSn.