Carbon doping of superconducting magnesium diboride

Abstract

We present details of synthesis optimization and physical properties of nearly single phase carbon doped MgB 2 with a nominal stoichiometry of Mg(B 0.8 C 0.2 ) 2 synthesized from magnesium and boron carbide (B 4 C) as starting materials. The superconducting transition temperature is ≈ 22 K (≈ 17 K lower than in pure MgB 2 ). The temperature dependence of the upper critical field is steeper than in pure MgB 2 with H c2 (10K) ≈ 9 T. Temperature dependent specific heat data taken in different applied magnetic fields suggest that the two-gap nature of superconductivity is still preserved for carbon doped MgB 2 even with such a heavily suppressed transition temperature. In addition, the anisotropy ratio of the upper critical field for T /T c ≈ 2 3 is γ ≈ 2. This value is distinct from 1 (isotropic) and also distinct from 6 (the value found for pure MgB 2 ).

Retention of two-band superconductivity in highly carbon-dopedMgB2

“…12 We further conclude that this result gives direct experimental evidence for the absence of interband impurity scattering, i.e. scenario (ii).…”

“…Much of the discrepancy is possibly a synthesis problem due to the slow kinetics of C incorporation. Mickelson et al, 11 and more recently Ribeiro et al, 12 have been able to overcome the diffusion problem by using a C containing starting material, B 4 C, and obtained samples with sharp diffraction peaks and superconducting transitions. The synthesis using B 4 C yields multiphase samples containing another borocarbide, MgB 2 C 2 , since the solubility limit of C in MgB 2 is less than the 20 atom% present in the starting B 4 C.…”

Role of carbon in enhancing the performance of MgB2 superconductor

“…3), are much higher than that of the substituted MgB 2-x C x samples. In the later case, the enhancement of J c (H) is entirely due to the disorder in σ band [9,12] Worth mentioning is the fact that breaking of doped nano-Carbon derivatives and ensuing substitution at B site in MgB 2 depends upon both nature of dopant and the heat treatment [13,[19][20][21]. For example, the n-SiC is more susceptible to react than n-Diamond [13,[19][20][21] at common MgB 2 synthesis temperatures.…”

ImprovedJcof MgB2superconductor by ball milling using different media

“…A significant enhancement in the J c of MgB 2 has been achieved through chemical doping with carbon (C) containing compounds, such SiC, C, B 4 C, and CNT. However, doping effects have been limited by the agglomeration of nanosized dopants and poor reactivity between boron (B) and C [2][3][4][5][6][7]. Moreover, the self-field and low-field J c were depressed due to the decrease in the superconducting volume.…”