Optical properties of ternary β electronphases based on NiAl

Optical constants of several ternary β Hume-Rothery phases have been investigated as a function of the valence electron concentration and defect structure. The composition of the alloys was based on the β phase NiAl, the absorption spectrum of which is dominated by two maxima at 2·5 and 4 eV. The intensity of the 2·5 eV-ε₂ peak is considerably increased with increasing valence-electron concentration, whereas that of the other peak is decreased. The valence electron concentration is varied by substituting Cu for Ni in Ni_1?yCu_yAl or Si for Al in NiAl_1?ySi_y. The 2·5 eV absorption peak disappears when Co is substituted for Ni in Ni_1?yCo_yAl. The absorption peaks are attributed to interband transitions of electrons and are discussed according to the rigid band model. The absorption in the infrared is explained by the scattering of electrons from lattice defects and phonons. The position of the d-band relative to the Fermi level is discussed in connection with s-d band scattering.