Cu 2p core-level XPS of Nd1.85Ce0.15CuOy: An analysis from bond valence sums and Madelung potentials.

Abstract

Cu 2p core-level spectra have been obtained on as-grown and reduced ${\mathrm{Nd}}_{1.85}$${\mathrm{Ce}}_{0.15}$${\mathrm{CuO}}_{\mathit{y}}$. The intensity ratio of the Cu 2p satellite to main peaks (${\mathit{I}}_{\mathit{s}}$/${\mathit{I}}_{\mathit{m}}$) is lower compared with the case of p-type cuprates. This characteristic is discussed on the basis of the crystal-chemical parameters. The bond valence sums (BVS) of each ion are calculated. It is found that the effective oxidation state of Cu is, in contrast to the p-type cuprate superconductors, less than 2+. The relationship among the BVS, the Madelung site potential difference \ensuremath{\delta}${\mathit{V}}_{\mathit{M}}$ between the in-plane O and Cu, and the Cu-O charge-transfer gap \ensuremath{\Delta} is discussed. It is pointed out that the relatively lower ${\mathit{I}}_{\mathit{s}}$/${\mathit{I}}_{\mathit{m}}$ of Cu 2p XPS spectra reflects the lower valence state of Cu, or relatively smaller values of \ensuremath{\Delta} as well as \ensuremath{\delta}${\mathit{V}}_{\mathit{M}}$.