X-ray photoemission spectroscopy study ofLaCuO3

The metallic rhombohedral (R3¯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 i i 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 i i i in an octahedral site linked to neighboring Cu i i i via a single 180° 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 i i i in square coplanar coordination and which is bridged to neighboring Cu i i i 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 ${\mathrm{LaCuO}}_3$.