Electronic structure ofBaPb1−xBixO3

Vacuum-prepared surfaces of $\mathrm{Ba}{\mathrm{Pb}}_{1-x}{\mathrm{Bi}}_x{\mathrm{O}}_3$ with $x=0, 0.25, \mathrm{and} 1$ were studied by x-ray photoelectron spectroscopy to elucidate the electronic structure and the valence states of bismuth in these compounds. Valence-band spectra give evidence for a shallow band in BaBi${\mathrm{O}}_3$, which is depopulated as Pb is substituted for Bi. The lack of asymmetry of the Ba core-electron lines indicates that there is no Ba $5d$ or $6s$ character at $E_F$. The asymmetry of the O $1s$ line, especially in BaPb${\mathrm{O}}_3$, indicates that this shallow band has largely O $2p$ character. The Bi $4f$ lines of BaBi${\mathrm{O}}_3$ were significantly broadened, but could not be unambiguously resolved into the two components expected on the basis of the crystal structure.