| Summary: | 碩士 === 國立東華大學 === 應用物理研究所 === 94 === In this thesis, the effect of Mn on the electrical resistivity (ρ), Seebeck coefficient (S), thermal conductivity (κ), as well as specific heat (Cp) of high temperature superconductors GdBa2(Cu1-xMnx)3O7-δ ( x = 0.0, 0.005, 0.0075, 0.01 and 0.02 ) was studied. It is found that the Seebeck coefficient changes sign from negative to positive upon 0.5% of Mn substitution, and the magnitude of S becomes larger with further Mn substitution. Such a result indicates that the substitution of Mn4+ ions for Cu2+ is effectively doping electrons to the system. An enhancement of thermal conductivity below transition temperature was observed for all samples, presumably due to the reduction of electron-phonon scattering as electrons condense into Cooper pairs. A jump in specific heat at the superconducting transition was observed for the low concentrations of Mn, however, the jump in Cp disappears for Mn concentration above 1%. Our present findings clearly demonstrate that the physical properties of GdBa2Cu3O7-δ superconductor are greatly affected by Mn substitution for Cu. These behaviors can be qualitatively understood by the change of carrier concentration and introduction of disorder to the lattice with Mn substitution.
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