| Summary: | 碩士 === 淡江大學 === 物理學系 === 87 === In order to study the variation of local structure around Cu due to Ca2+ doping
and the different the rare earth ion size. We have performed the extended X-ray
absorption fine structure (EXAFS) on R1-xCaxBa2Cu3O7- (x=0，0.1，0.2；R=Y，Gd，
Nd) samples at room temperature. By fitting the Cu K-edge experimental data, we
obtain the following conclusions：In the Gd system, Cu-O bond distances increase
with Ca2+ doping, and Cu(2)-O plane is disorder because of counterbalance effect.
There no apparent change in the coordination number of O surrounding Cu, which
indicates that in our samples the decreases of superconducting transition temperature
Tc is not due to oxygen vacancies. When the static disorder of the surrounding atoms
increases, the superconducting transition temperature Tc decreases. When the radius
of the R3+ ion increases, the increases of the static disorder will decreases the normal-
state resistivity.
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