The High Oxygen Pressure Synthesis of Metallic LaCuO3 and the XPS Study on Cu3+ State
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摘要: 本文在成功地用超高氧压（~6.5 GPa）及高温（~980 ℃）合成和结构测定的基础上，首次对金属性化合物中LaCuO3中的Cu3+离子给予标定，并研究了它与绝缘体中Cu3+的区别。本论文中合成的LaCuO3为金属性化合物，电导率测量表明在大于13 K无超导电性迹象。XPS测量给出了LaCuO3中Cu2p3/2内层电子结合能相对于La2CuO4或CuO中的Cu2+向高结合能方向移动了约2.6 eV，这一量值远大于NaCuO2（绝缘体）中的Cu2p3/2相对于CuO中的Cu2+移动的值，约为1.3 eV。Auger谱测量表明，LaCuO3的修正了的Auger参数与CuO的基本相同，但L3VV的Auger电子动能相对CuO移动了2.8 eV。这些位移说明在金属性化合物LaCuO3中，Cu3+处在八面体位置上，它与近邻的Cu3+连成单个CuOCu桥，因此可作为对比p型高Tc含铜氧化物的XPS谱的标准。Abstract: 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.
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Key words:
- LaCuO3 /
- synthesis under high oxygen pressure /
- XPS /
- Cu3+ state
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