Optical Properties of Copper-Rich Cu-Ni-Zn Alloys with 20 at.% Zinc and up to 25 at.% Nickel at Room Temperature

Normal-incidence reflectance measurements on mechanically polished specimens of copper-rich copper nickel zinc alloys with up to 25 at.% nickel and about 20 at.% zinc were obtained in the photon energy range 1.55-5.18 eV. These measurements were taken at room temperature under vacuum (lower than 10^-7 Torr). The absorption edge associated with interband transitions which is observed between 2 and 3.2 eV is, within experimental accuracy, independent of nickel concentration. This indicates that nickel and zinc atoms do not interact directly. At nickel concentrations above 5 at.%, a reflectance minimum appears near 4 eV. The position of this minimum shifts with increasing nickel concentration to higher energies. The width and the depth of the minimum increases as the concentration of nickel is increased. It is similar to the reflectance minimum which pure nickel exhibits near 4 eV.