Experimental and theoretical studies of optical properties on alloys of the intermetallic systems Li2Ag2−x In x and Li2Cd2−x In x

X-ray and neutron diffraction experiments and optical studies were done on several alloys of the quasibinary series Li₂Ag_2−x In _x , Li₂Cd_2−x In _x , and Li₂Zn_2−x Cd _x . Within a wide region the alloys crystallize homogenous in an NaTl-type structure (1≦x≦1.5 for Li₂Ag_2−x In _x ; 0.6≦x≦1 for Li₂Cd_2−x In _x ; 1.2≦x≦1.6 for Li₂Zn_2−x Cd _x ). Most of the alloys investigated are colored and the color changes continuously as a function ofx. Measurements of the reflectivityr and the dielectric constants (ɛ₁ and ɛ₂) were done in the energy range 1.5 eV≦E≦3.3 eV by the method of elliptical analysis. In this energy range the curvesr(E) have minima which shift with increasingx to lower energy values. Calculations of the energy bands of LiAg, LiIn, LiCd, and Li₂AgIn on the basis of the augmented plane wave method and the determination of the joint density show that the optical data can be interpretated on the assumption of interband transitions between the valence and the conduction bands and of transitions between the 4d-bands of silver and the energy states at the Fermi level.