| Summary: | 碩士 === 國立中央大學 === 物理研究所 === 98 === The transport characteristics and superconductivity of Sn/In2O3 nanocomposites were studied. The measurement of magnetic susceptibility, magnetization, and electron transport measurement were performed using the Quantum Design PPMS. The two set of Sn/In2O3 nanocomposites studied were prepared by mixing the Sn and In2O3 nanopartilces with different mass ratio and being cold compressed into pellets. The obtained nanocomposites have packing fraction f=62.5 %(three samples) and f=75 %(six samples), respectively.
The number of In2O3 nanoparticles between Sn nanoparticles will affect the transport of superconducting pairs. Only the pure tin sample shows the phenomenon that the resistivity decrease rapidly in f=62.5 % samples. On the other hand, in f=75 % samples that when the ratio of In2O3 comes to 15 % and 20 %, there is more than one In2O3 nanoparticles around Sn nanoparticles. This result causes the tunneling probability of superconducting electron pairs becomes smaller but the system still exist the phenomenon of rapidly decreasing resistivity.When the samples which have the most ratio of In2O3(20 % for f=62.5 % and 25% for f=75 %), the resistivity increases rapidly instead of superconducting transition. We use hopping model to describe the electron transport of these two samples.
We found two special phenomena on I-V curve of the f=62.5 % sample is named Sn_A. Upon the superconducting temperature, the curve increases linearly to a threshold point and then decreases rapidly shows
that electrons move without hindrance. This threshold point shifts to higher excitation current with increasing temperature. The other one is that slopes before the threshold point become smaller with increasing temperature. The reason is supposed that the temperature will make the tunneling barrier become higher and it will excite electrons from valance band through the energy gap to conduction band for conducting.
Irreversible MR curves were observed in the high temperature regime, this behavior will become apparent with increasing temperature, increasing excitation current and in the In2O3 rich samples.
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