X-ray photoemission spectroscopy study of LaCuO3.

Abstract

The metallic rhombohedral (R3\ifmmode\bar\else\textasciimacron\fi{}c), perovskite ${\mathrm{LaCuO}}_{3}$ has been synthesized under a high pressure of oxygen. The Cu 2${\mathit{p}}_{3/2}$ x-ray photoemission spectroscopy (XPS) peak exhibits a shift of 2.6 eV to higher binding energy relative to that of Cu ii in CuO and ${\mathrm{La}}_{2}$${\mathrm{CuO}}_{4}$. The modified Auger parameter is of comparable magnitude in the two compounds and the ${\mathit{L}}_{3}$VV Auger-electron kinetic energy is shifted by 2.8 eV relative to that of CuO. These shifts are representative of Cu iii in an octahedral site linked to neighboring Cu iii via a single 180\ifmmode^\circ\else\textdegree\fi{} Cu-O-Cu bridge in a metallic phase. This spectrum is therefore a useful standard for comparison with the XPS spectra of the p-type high-${\mathit{T}}_{\mathit{c}}$ copper oxides. The present standard is the XPS spectrum of the insulator ${\mathrm{NaCuO}}_{2}$, which contains Cu iii in square coplanar coordination and which is bridged to neighboring Cu iii by two oxygen bridges having a Cu-O-Cu bond angle approaching 90?; its chemical shift is 1.3 eV smaller than that of metallic ${\mathrm{LaCuO}}_{3}$.