Optical properties and electronic structure ofβ′−NiAl

The optical constants and their temperature derivatives have been determined for ${\beta }^{\prime }-\mathrm{NiAl}$ from absorption and thermoreflectance measurements in the energy range of 0.2-4.4 eV. The results are interpreted using the self-consistent energy bands of Moruzzi, Williams, and Gelatt. By comparing a calculated joint density of states with ${\epsilon }_2$, the imaginary part of the dielectric function, good overall agreement is found between theory and experiment. In contrast to earlier analyses, it is found that the 2.5-eV peak in ${\epsilon }_2$ is primarily due to direct interband transitions terminating near the Fermi surface. This new interpretation of the 2.5-eV feature is discussed in relation to previously reported concentration effects and the rigid-band model.