Electronic structure of Nb-Mo alloys

Thermoreflectance measurements on ${\mathrm{Nb}}_x{\mathrm{Mo}}_{1-x}$ alloys ($x=0.2, 0.5, 0.8$) have been carried out in the 0.5-5.0 eV energy region. Augmented-plane-wave (APW) calculations for Nb at two different lattice parameters and for Mo, as well as coherent-potential-approximation calculations (CPA), have been carried out and have been used in the interpretation of the experimental results. Several optical transitions [${\Sigma }_1\left(E_F\right)\to {\Sigma }_3$, $G_4\left(E_F\right)\to G_1$,$N_2\to {N^{\prime }}_1$], have been identified, and their concentration dependence followed. These results contribute significantly toward putting the interpretation of the optical properties of Nb, Mo, and their alloys on a much more secure footing. In particular, it has been confirmed that while the lower conduction bands behave roughly as predicted by the rigid-band model, the higher-lying conduction bands show distinctly non-rigid-band-like behavior.