Electronic Structure of the High-$T_c$ Superconductor ${\mathrm{Ba}}_{1-x}{\mathrm{K}}_x{\mathrm{BiO}}_3$

Band-structure results for ordered ${\mathrm{Ba}}_{0.5}$ ${\mathrm{K}}_{0.5}$Bi${\mathrm{O}}_3$ alloys confirm that the antibonding $\mathrm{Bi}\mathrm{}\left(6s\right)-\mathrm{O}\mathrm{}\left(2p\right)\mathrm{}$ conduction band near $E_F$ in cubic BaBi${\mathrm{O}}_3$ is minimally affected by substitutional K doping at the $A\left(\mathrm{Ba}\right)$ site. This supports the prediction that $A$-site doping would extend the metallic range of ${\mathrm{Ba}}_{1-x}{\mathrm{K}}_x{\mathrm{BiO}}_3$ closer to half filling (BaBi${\mathrm{O}}_3$) than $B$-site doping (${\mathrm{BaPb}}_{1-y}{\mathrm{Bi}}_y{\mathrm{O}}_3$), thereby increasing both the coupling of the conduction electrons to bond-stretching O phonons and $T_c$. ${\mathrm{Ba}}_{1-x}{\mathrm{T}}_x{\mathrm{PbO}}_3$, where $T$ is trivalent, might also exhibit favorable superconducting properties.