Half-Heusler phases have gained recently much interest as thermoelectric
materials. Screening of possible systems was performed by ab-initio simulation
using VASP-software. The energy-versus-Volume (E(V)) curves were calculated and
calibrated. For TiCoSb, NbNiSn, FeMoSb the stability of Half-Heusler phase
against concurrent crystal structures like TiNiSi, ZrCoAl, ZrBeSi, FeSiV, ZrNiP
and Full Heusler was confirmed. However, the thermo-dynamical driving force as
calculated from the difference in lattice energies is less than 0.1eV/atom.
Hence, the fabrication of Half Heusler phases is a challenge and requires three
steps, surface activation of the raw material by ball milling, arc-melting of
pressed pellets and finally long-term annealing treatment in a vacuum furnace.
On doped TiCoSb specimens, Seebeck coefficients up to 0.1 mV/K, on NiNbSn 0.16
mV/K were measured, although the microstructure was not yet optimized.Comment: 6 pages, 5 figures, 2 table