Limiting factors of normal-state conductivity in superconducting MgB2: an application of mean-field theory for a site percolation problem
Limiting factors of normal-state conductivity in superconducting MgB2: an application of mean-field theory for a site percolation problem
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DOI：
10.1088/0953-2048/20/7/012
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发表时间：
2007-07
影响因子：
3.6
通讯作者：
A. Yamamoto;J. Shimoyama;K. Kishio;T. Matsushita
中科院分区：
文献类型：
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作者：
A. Yamamoto;J. Shimoyama;K. Kishio;T. Matsushita
研究了具有系统变化的填充因子的多晶MgB_2块体样品的正常态电导。用三维位渗流模型很好地解释了声子项电阻率Δρ(T)=ρ(T)−ρ0与填充因子的关系。认为样品的低堆积密度和晶界处的湿杂质相是导致MgB_2电性差的主要原因。我们的模型能够定量地评估多晶样品中颗粒内部的本征电阻率、能够载流的活性颗粒的比例以及颗粒的各向异性。该模型预测，在渗流问题的情况下，可以理解相当弱连接的无连接的MgB_2中的反常抑制连通性。
Normal-state conductivity in polycrystalline MgB2 bulk samples having a systematically varied packing factor was studied. The packing factor dependence of phonon term resistivity Δρ(T) = ρ(T)−ρ0 was found to be well explained by the three-dimensional site percolation model. The low packing density of the samples and the wet impurity phases at grain boundaries are suggested to be the main causes of poor electrical connectivity in MgB2. Our model enables quantitative evaluations of the intrinsic resistivity inside the grains, the fraction of the active grains that can carry current and the anisotropy of the grains in polycrystalline samples. The model predicts that the anomaly suppressed connectivity in rather weak-link-free MgB2 can be understood under a scenario of a percolation problem.