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تسجيل مستخدم جديدSuperconductivity of bulk MgB2 + nano(n)-SiC composite system: A high field magnetization study
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We study the effect of nano(n)-SiC addition on the crystal structure, critical temperature (Tc), critical current density (Jc) and flux pinning in MgB2 superconductor. X-ray diffraction patterns show that all the samples have MgB2 as the main phase with very small amount of MgO, further with n-SiC addition the presence of Mg2Si is also noted and confirmed by SEM & EDS. The Tc value for the pure MgB2 is 18.9K under 8 Tesla applied field, while is 20.8K for the 10-wt % n-SiC doped sample under the same field. This points towards the increment in upper-critical field value with n-SiC addition. The irreversibility field (Hirr) for the 5% n-SiC added sample reached 11.3, 10 and 5.8 Tesla, compared to 7.5, 6.5, and 4.2 Tesla for the pure MgB2 at 5, 10 and 20K respectively. The critical current density (Jc) for the 5-wt % n-SiC added sample is increased by a factor of 35 at 10K and 6.5 Tesla field and by a factor 20 at 20K and 4.2 Tesla field. These results are understood on the basis of superconducting condensate (sigma band) disorder and ensuing intrinsic pining due to B site C substitution clubbed with further external pinning due to available n-SiC/Mg2Si pins in the composite system.
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We study the effect of synthesis temperature on the phase formation in nano(n)-SiC added bulk MgB2 superconductor. In particular we study: lattice parameters, amount of carbon (C) substitution, microstructure, critical temperature (Tc), irreversibili
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temperature (Tc) is not affected significantly by x up to x = 0.05 and latter decreases slightly for higher x > 0.05. R(T) vs H measurements show higher Tc values under same applied magnetic fields for the nano-diamond added samples, resulting in higher estimated Hc2 values. From the magnetization measurements it was found that irreversibility field value Hirr for the pristine sample is 7.5 Tesla at 4 K and the same is increased to 13.5 Tesla for 3-wt% nD added sample at the same temperature. The Jc(H) plots at all temperatures show that Jc value is lowest at all applied fields for pristine MgB2 and the sample doped with 3-wt% nD gives the best Jc values at all fields. For the pure sample the value of Jc is of the order of 105 A/cm2 at lower fields but it decreases very fast as the magnetic field is applied and becomes negligible above 7 Tesla. The Jc is 40 times higher than pure MgB2 at 10 K at 6 Tesla field in case of 3%nD doped sample and its value is still of the order of 103 A/cm2 at 10 Tesla for the same sample. On the other hand at 20K the 5%nD sample shows the best performance at higher fields. These results are discussed in terms of extrinsic pinning due to dispersed n-Diamond in the host MgB2 matrix along with the intrinsic pinning due to possible substitution of C at Boron site and increased inter-band scattering for highly doped samples resulting in extraordinary performance of the doped system.
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