Berlin 2008 – scientific programme

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MM: Fachverband Metall- und Materialphysik

MM 28: Intermetallic Phases I

MM 28.2: Talk

Wednesday, February 27, 2008, 17:45–18:00, H 0107

Fabrication of CoTiSb and NbNiSb Half-Heusler phases for thermoelectric applications --- NOTE: This talk has been withdrawn — •Wilfried Wunderlich, Yoshikaji Aoki, Kousuke Nakatsuka, Hideto Ueno, and Yuichiro Motoyama — Tokai University, Fac. Eng, Materials Science Dept., Hiratsuka-shi, Kanagawa, Japan

Important applications of Half-Heusler phases are as thermoelectric materials. For the cases of CoTiSb, TiNiSn and others, ab-initio simulation using VASP-software could confirm the phase stability against phases with concurrent crystal structures like TiNiSn, ZrCoAl, ZrBeSi, FeSiV and Full Heusler. However, the thermo dynamical driving force for formation as calculated from the difference in lattice energies is less than 0.1eV/atom. Hence, the fabrication of Half heusler phases is difficult and requires three steps, surface activation of the raw material by ball milling, arc-melting of pressed pellets and finally long-term annealing treatment. For the CoTiSb system, diffusion couple experiments clarified the complicated diffusion mechanism, which can lead in worst cases to Kirkendahl voids and constitutional vacancies. On doped CoTiSb specimens, Seebeck coefficients up to 0.1 mV/K, on NiNbSb 0.3 mV/K were measured.