XRD pattern of superconducting composite. Only diffraction peaks of and MgO phases were detected. The mass ratio of to MgO in the sample was calculated to 1:2.6.
curves of superconducting composite and pure bulk. The inset shows their curves in the vicinity of N–S transition.
The volume fraction dependence of composite’s conductivity calculated by SB, CM, SP, and ML approximations. The inset shows the normalized conductivity of W– composite: “○” refers to the experimental data, (Ref. 32) “—” SP result at , and ML approximation at .
Diagram of a simple model for the temperature dependence of composite volume fraction.
Fitting the resistance-temperature data of superconducting composite from 50 to 300 K by the SPT approximation. Solid circle symbols refer to experimental values and the solid line refers to the fitting result. The inset is the fitting and at range from 2.0 to 3.0. The maximum and minimum of were obtained at .
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