Improved critical current density of MgB 2-carbon nanotubes composite

Abstract

In the present study, we report a systematic study of doping/admixing of carbon nanotubes (CNTs) in different concentrations in MgB 2. The composite material corresponding to MgB 2 - x at.% CNTs (35 at.% ≥ × ≥ 0 at.%) have been prepared by solid-state reaction at ambient pressure. All the samples in the present investigation have been subjected to structural/microstructural characterization employing XRD, Scanning electron microscopic (SEM), and Transmission electron microscopic (TEM) techniques. The magnetization measurements were performed by Physical property measurement system (PPMS) and electrical transport measurements have been done by the four-probe technique. The microstructural investigations reveal the formation of MgB 2-carbon nanotube composites. A CNT connecting the MgB 2 grains may enhance critical current density due to its size (∼5-20 nm diameter) compatible with coherence length of MgB 2 (∼5-6 nm) and ballistic transport current carrying capability along the tube axis. The transport critical current density (J ct) of MgB 2 samples with varying CNTs concentration have been found to vary significantly e.g., J ct of the MgB 2 sample with 10 at.% CNT addition is ∼2.3 × 10 3 A/cm 2 and its value for MgB2 sample without CNT addition is ∼7.2 × 102 A/cm2 at 20 K. In order to study the flux pinning effect of CNTs doping/ admixing in MgB2, the evaluation of intragrain critical current density (J c) has been carried out through magnetic measurements on the fine powdered version of the as synthesized samples. The optimum result on J c is obtained for 10 at.% CNTs admixed MgB 2 sample at 5 K, the J c reaches ∼5.2 × 106 A/cm 2 in self field, ∼1.6 × 106 A/cm 2 at 1 T, ∼2.9 × 105 A/cm 2 at 2.6 T, and ∼3.9 × 104 A/cm 2 at 4 T. The high value of intragrain J c in 10 at.% CNTs admixed MgB 2 superconductor has been attributed to the incorporation of CNTs into the crystal matrix of MgB 2, which are capable of providing effective flux pinning centres. A feasible correlation between microstructural features and superconducting properties has been put forward. Copyright © 2007 American Scientific Publishers All rights reserved.