Band-Theoretic Study of the Metallic Character of the Alkali—Noble Metal Alloys

Abstract

The electronic band structures of CsAu and LiAg have been determined by a combination of the Green's function (KKR) and the quantum-defect (QDM) methods. The construction of the phase shifts is based on the preliminary determination of the appropriate quantum defects. The latter are adjusted to take into account an estimated charge transfer of $0.55e$ from alkali to the noble metal. Our results show that despite the similarily of their constituents and of their crystal structures the two alloys exhibit markedly different features: CsAu is an extrinsic $n$-type semiconductor with a 2.7-eV minimum gap in the (111) direction, while LiAg has the band structure of a metallic alloy, with the (cubic) Brillouin zone full except for small empty regions at the corners. Our results for CsAu are in agreement with available data and with one previous calculation. For LiAg, there are no experimental data available for comparison.