Structural and defect analysis of V-alloyed C15 NbCr2 from high resolution synchrotron X-ray powder diffraction

The structural and defect characteristics of V-alloyed C15 Laves phase based on NbCr2 have been studied using a combination of high-resolution synchrotron X-ray powder diffraction and Rietveld structure refinement. The results show that V atoms substitute on the Cr site in the C15 structure, in spite of the fact that the atomic radii of the three elements indicate that r(Cr) < r(V) < r(Nb). It is also found that the lattice parameter increases linearly with increasing V content, suggesting a random occupancy of V on the Cr site. The alloying behaviour and the defect structures are qualitatively explained in terms of the electronic structure of C15 NbCr2 obtained by first-principles total energy and electronic structure calculations.