Influence of Disorder on the Bad Metal Behavior in Polar Amalgams

The two new ternary amalgams K_1-RbHg₁₁ [x = 0.472(7)] and Cs_3-CaHg₂₀ [x = 0.20(3)] represent two different examples of how to create ternary compounds from binaries by statistical atom substitution. K_1-RbHg₁₁ is a Vegard-type mixed crystal of the isostructural binaries KHg₁₁ and RbHg₁₁ [cubic, BaHg₁₁ structure type, space group Pm3̅m, a = 9.69143(3) Å, Rietveld refinement], whereas Cs_3-CaHg₂₀ is a substitution variant of the Rb₃Hg₂₀ structure type [cubic, space group Pm3̅n, a = 10.89553(14) Å, Rietveld refinement] for which a fully substituted isostructural binary Ca phase is unknown. In K_1-RbHg₁₁, the valence electron concentration (VEC) is not changed by the substitution, whereas in Cs_3-CaHg₂₀, the VEC increases with the Ca content. Amalgams of electropositive metals form polar metal bonds and show "bad metal" properties. By thermal analysis, magnetic susceptibility and resistivity measurements, and density functional theory calculations of the electronic structures, we investigate the effect of the structural disorder introduced by creating mixed-atom occupation on the physical properties of the two new polar amalgam systems.