Optical constants of some silver alloys

Abstract

The optical constants between 1.40 and 5.25 eV of three disordered alloy systems, AgCd, AgMg, and AgSn, have been directly measured over their respective $\ensuremath{\alpha}$-phase ranges. The measurements indicate that the onset of the ${{L}_{2}}^{\ensuremath{'}}\ensuremath{-}{L}_{1}$ transitions in pure Ag occurs at 3.33 \ifmmode\pm\else\textpm\fi{} 0.08 eV. The measurements clearly show the delineation of the alloys into two classes, one called class $A$, where the formalism of periodic structures with direct optical transitions is applicable, and one called class $B$, where this formalism is not applicable, and indirect optical transitions dominate in the changes caused by alloying. The plasma frequency in the Drude region is found to be a constant for these alloys within experimental error. For both of the class-$A$ alloys, AgMg and AgCd, the electronic structure is very similar and a non-rigid-band variation of energy levels is found which can be qualitatively understood in terms of alloy theory. AgSn is a class-$B$ alloy, the understanding of which is more difficult.