Photoelectron spectroscopic study of ${\mathrm{Ba}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Rb}}_{\mathit{x}}$${\mathrm{BiO}}_3$

A photoelectron spectroscopic study to investigate the electronic structure of a noncuprate oxide superconductor ${\mathrm{Ba}}_{1\mathrm{-}\mathit{x}}$ ${\mathrm{Rb}}_{\mathit{x}}$ ${\mathrm{BiO}}_3$ (0≤x≤0.4) system is reported. Comparison of the results with those inconclusively reported for ${\mathrm{Ba}}_{1\mathrm{-}\mathit{x}}$ ${\mathrm{K}}_{\mathit{x}}$ ${\mathrm{BiO}}_3$ and ${\mathrm{BaPb}}_{1\mathrm{-}\mathit{x}}$ ${\mathrm{Bi}}_{\mathit{x}}$ ${\mathrm{O}}_3$ is discussed. It is concluded that the chemical environment of substituted Rb in this system is similar to that of Rb metal, core-level binding energies of Bi and Ba are unaffected by Rb substitution, and the shift of the valence band towards lower binding energy upon hole-carrier doping is observed. A characteristic change of the density of states in the vicinity of the Fermi level with composition x is observed, suggesting that the nonmetal-to-metal transition occurs through a continuous change of the electronic states of the system.