摘要
The effect of Y substitution for Ca on the crystal structure and electronic states of Bi_2Sr_2CaCu_2O_(8+y) was studied. It is found that the modulation period of the incommensurate superlattice along b axis decreases from 4.7b to about 4.0b gradually, which implies the change of the extra oxygen atoms residing within double Bi-O layers. Two kinds of modulation structures with periods of 4b and 8b exist in the same compound as Ca is completely substituted by Y. XPS was employed to study the change in the electronic structure. The results suggest that the variation of superconductivity is not caused by the slight change in crystal structure, but rather by the hole filling in O2p orbitals in CuO_2 layers. For this substituted system, it is still the case where one hole in Cu3d orbital (3d^9) is corresponding to the strong correlation antiferromaguetic insulator, and an extra hole in O2p orbital in CuO_2 layer (3d^9L) to the superconductor.
The effect of Y substitution for Ca on the crystal structure and electronic states of Bi<sub>2</sub>Sr<sub>2</sub>CaCu<sub>2</sub>O<sub>8+y</sub> was studied. It is found that the modulation period of the incommensurate superlattice along b axis decreases from 4.7b to about 4.0b gradually, which implies the change of the extra oxygen atoms residing within double Bi-O layers. Two kinds of modulation structures with periods of 4b and 8b exist in the same compound as Ca is completely substituted by Y. XPS was employed to study the change in the electronic structure. The results suggest that the variation of superconductivity is not caused by the slight change in crystal structure, but rather by the hole filling in O2p orbitals in CuO<sub>2</sub> layers. For this substituted system, it is still the case where one hole in Cu3d orbital （3d<sup>9</sup>） is corresponding to the strong correlation antiferromaguetic insulator, and an extra hole in O2p orbital in CuO<sub>2</sub> layer （3d<sup>9</sup>L） to the superconductor.
基金
Project supported by the National Natural Science Foundation of China and by the Laboratory of Structure and Element Analysis, Academia Sinica
