The High Oxygen Pressure Synthesis of Metallic LaCuO3 and the XPS Study on Cu3+ State

In this work, on the basis of LaCuO3 synthesized at high oxygen pressure (~6.5 GPa) and temperature (~980 ℃) and of its structure determination, the Cu3+ ion in metallic state was first characterized, and the difference between the metallic and insulator state was studied. The compound of LaCuO3 synthesized in this study is a metallic one which does not show superconductivity until 13 K by resistivity measurements. The XPS measurements show that the Cu2p3/2 core level in LaCuO3 shifts to higher binding energy about 2.6 eV relative to that of Cu2+ in La2CuO4 or CuO, this value is 1.3 eV higher than the relative shift value of Cu2p3/2 in NaCuO2 (insulator) to Cu2+ in CuO. The measurement of Auger line indicates that the modified Auger parameters of LaCuO3 are comparable to CuO but the L3VV Auger-electron kinetic energy shifts by 2.8 eV relative to that of CuO. These shifts indicate that the Cu3+ is in an octahedral site linked to neighboring Cu3+ via a single 180CuOCu bridge in a metallic phase. This spectrum is, therefore, can be used as a useful standard for comparison with the XPS spectra of the p-type high-Tc copper oxides.