Optical Constants of β-Phase NiAl

Abstract

The optical constants of nine compounds of NiAl ranging in composition from 45.2 at.% Ni to 61.6 at.% Ni have been determined between 0.212 and 1.80 μ. Measurements of the ratio of the reflectance of light polarized parallel to the plane of incidence to the reflectance of light polarized perpendicular to the plane of incidence were made at the following five angles of incidence: 55°, 60°, 65°, 70°, 75°. Data were analyzed by a computerized interation technique to provide values of the high‐frequency dielectric constants and the electrical conductivity. Since the measurements were made on mechanically polished surfaces, two annealing experiments were performed to ascertain the effects of surface disturbance; the results showed that the optical properties were essentially unaffected by the annealing treatments. Plots of 2nk show absorption bands at ≈1.5 to 2, 2.5, 4.0, and 5.1 eV and what may be interpreted as free‐electron behavior below 1.5 eV. The energy‐band structure shows a strong compositional dependence which has been interpreted to be the result of contact between the Fermi surface and a Brillouin‐zone boundary.