Barium contributions to the valence electronic structure ofYBa2Cu3O7−δ,PrBa2Cu3O7−δ, and other barium-containing compounds

Monochromatic photon beams were used to excite barium ${\mathit{N}}_{\mathrm{I}\mathrm{V},\mathrm{V}}$ soft x-ray emission spectra from ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$, ${\mathrm{PrBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$, ${\mathrm{BaF}}_2$, and ${\mathrm{BaTiO}}_3$. Near threshold excitation was used to demonstrate that small contributions to the barium ${\mathit{N}}_{\mathrm{V}}$ and ${\mathit{N}}_{\mathrm{IV}}$ emission spectra in the energy region above the 5p→4d core-core transitions do not arise as satellite emission from transitions in multiply excited atoms but rather occur as a result of transitions from the valence states. The emission spectrum of ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$ and ${\mathrm{PrBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$ reveals a contribution to the electronic density of states at the barium site in the region near the Fermi level. The ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$ compound is a superconductor and ${\mathrm{PrBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$ is an insulator. It has been proposed that the difference between them is due to mixing of praseodymium and barium among the sites occupied by yttrium and barium, with an accompanying change in electronic structure. However, our measurements indicate that the barium partial density of states for the two compounds are essentially identical.