X-RAY-ABSORPTION STUDIES OF ELECTRON DOPING AND BAND SHIFTS IN R(2-X)CE(X)CUO(4-DELTA) (R=PR, ND, SM, EU, AND GD)

被引:41
作者
LIANG, G
GUO, Y
BADRESINGH, D
XU, W
TANG, YJ
CROFT, M
CHEN, J
SAHINER, A
O, BH
MARKERT, JT
机构
[1] SAM HOUSTON STATE UNIV,DEPT CHEM,HUNTSVILLE,TX 77341
[2] RUTGERS STATE UNIV,DEPT PHYS,PISCATAWAY,NJ 08855
[3] UNIV TEXAS,DEPT PHYS,AUSTIN,TX 78712
来源
PHYSICAL REVIEW B | 1995年 / 51卷 / 02期
关键词
D O I
10.1103/PhysRevB.51.1258
中图分类号
T [工业技术];
学科分类号
08 ;
摘要
We have measured the polarized x-ray-absorption spectra at the Cu K edge of Nd2-xCexCuO4-δ single crystals and the unpolarized spectra of R2-xCexCuO4-δ (R=Pr, Nd, Sm, Eu, and Gd) ceramic samples. The results indicate that up to the T '-phase stability limit (and including the narrow region of superconductivity), Ce doping continuously donates electrons into the Cu 3d orbitals. Our results evidence a Cu1+ content in these T '-phase materials which increases almost linearly with the Ce-doping level x, and an electron doping fraction from each Ce atom to Cu which is quite close to unity (except in the R=Gd series). It is found that the size variation of the rare-earth elements R causes a number of feature changes in the Cu K edge, including an about 0.5 eV upward edge shift. These effects are explained by the ligand field shift of the unoccupied Cu 4p and 3d bands. A cluster model description has been developed to correlate the spectral features of the Cu K-edge spectra to different 3d configurations. The experimental results can be well described by the following model parameters: Cu 1s-3d Coulomb interaction Ucd∼6.5 eV, Cu 1s-O 2p Coulomb interaction UcL∼1.1 eV, d-ligand hybridization V∼2.7 eV, CuO charge-transfer energy Δ∼1.3 eV (at x=0), and Δ∼0.5 eV (at x=0.2). © 1995 The American Physical Society.
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页码:1258 / 1269
页数:12
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