Zr-based nickel aluminides: Crystal structure and electronic properties

In our motive to contribute to a better understanding of phase transitions, structural changes and physical properties of Zr-based alloys, we have studied three zirconium-rich compounds in the Zr–Ni–Al system annealed at 800 °C. For Zr6NiAl2, which was investigated hitherto only by the use of X-ray powder film data, the precise crystal structure has been derived from Rietveld refinement of powder X-ray diffraction data revealing a significant disorder of Al (81.3% Al+18.7% Ni in 2d) and Ni (76.1%Ni+23.9% Al in 1a) atomic sites rendering final composition Zr6Ni1.14Al1.86 in accord with energy dispersive X-ray (EDX) spectroscopy analysis. The crystal structures of ZrNiAl and Zr5Ni4Al have been confirmed; despite the disorder of certain atom sites (94% Al+6% Ni in 3g and 90% Ni+10%Al in 2d for ZrNiAl; 93% Zr+7% Al in 2e and 95% Al+5% Zr in 2f for Zr5Ni4Al; Rietveld refinements of powder X-ray diffraction data), the deviations from the stoichiometry for these compounds are negligible. Cell parameters and atomic coordinates have been also refined in the scope of local density approximation being in good agreement with experimental data. For all compounds the electronic density of states has been calculated. Electrical resistivity measurements characterize ZrNiAl, Zr6NiAl2 and Zr5Ni4Al as metals in concord with electronic band structure calculations.