Electronic states in rare-earth 1:2:3 oxides: Photoemission and Raman studies

Abstract

X-ray photoemission spectra (XPS) and Raman measurements of ${\mathrm{Y}}_{1\mathrm{-}\mathit{x}}$ ${\mathrm{Eu}}_{\mathit{x}}$ ${\mathrm{Ba}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_7$ and ${\mathrm{Eu}}_{1\mathrm{-}\mathit{x}}$ ${\mathrm{Pr}}_{\mathit{x}}$ ${\mathrm{Ba}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_7$ are compared to those of ${\mathrm{Y}}_{1\mathrm{-}\mathit{x}}$ ${\mathrm{Pr}}_{\mathit{x}}$ ${\mathrm{Ba}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_7$. It is shown that, with increasing x, the binding energies of the Ba core levels of ${\mathrm{Eu}}_{1\mathrm{-}\mathit{x}}$ ${\mathrm{Pr}}_{\mathit{x}}$ ${\mathrm{Ba}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_7$ shift towards higher values as in ${\mathrm{Y}}_{1\mathrm{-}\mathit{x}}$ ${\mathrm{Pr}}_{\mathit{x}}$ ${\mathrm{Ba}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_7$, while those of ${\mathrm{Y}}_{1\mathrm{-}\mathit{x}}$ ${\mathrm{Eu}}_{\mathit{x}}$ ${\mathrm{Ba}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_7$ do not, despite similar changes in Ba-O interatomic distances in the latter two systems. Raman measurements of ${\mathrm{Y}}_{1\mathrm{-}\mathit{x}}$ ${\mathrm{Pr}}_{\mathit{x}}$ ${\mathrm{Ba}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_7$ show a frequency increase of the Ba and apical-oxygen modes with increasing x, but a much smaller frequency increase in ${\mathrm{Y}}_{1\mathrm{-}\mathit{x}}$ ${\mathrm{Eu}}_{\mathit{x}}$ ${\mathrm{Ba}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_7$. The XPS and Raman results reflect changes in the Ba-O hybridization and correlate with both the suppression of superconductivity in both ${\mathrm{Y}}_{1\mathrm{-}\mathit{x}}$ ${\mathrm{Pr}}_{\mathit{x}}$ ${\mathrm{Ba}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_7$ and ${\mathrm{Eu}}_{1\mathrm{-}\mathit{x}}$ ${\mathrm{Pr}}_{\mathit{x}}$ ${\mathrm{Ba}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_7$, and with the retention of superconductivity in ${\mathrm{Y}}_{1\mathrm{-}\mathit{x}}$ ${\mathrm{Eu}}_{\mathit{x}}$ ${\mathrm{Ba}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_7$.