X-RAY PHOTOEMISSION SPECTROSCOPY STUDY OF LACUO3

The metallic rhombohedral (R3c), perovskite LaCuO3 has been synthesized under a high pressure of oxygen. The Cu 2p3/2 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 La2CuO4. The modified Auger parameter is of comparable magnitude in the two compounds and the L3VV 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°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-Tc copper oxides. The present standard is the XPS spectrum of the insulator NaCuO2, 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 LaCuO3. © 1990 The American Physical Society.