Significant improvements of the high-field properties of carbon-doped MgB₂ films by hot-filament-assisted hybrid physical–chemical vapor deposition using methane as the doping source

Abstract

We report a significant enhancement in upper critical field Hc2 and irreversibility field Hirr in carbon-doped MgB2 films fabricated by hot-filament-assisted hybrid physical–chemical vapor deposition (HFA-HPCVD) using methane as the doping source. For the parallel field, a very large temperature derivative value of 3 T K−1 near Tc was achieved in a heavily doped film with Tc near 28 K. Carbon doping also enhanced flux pinning, resulting in a much higher critical current density in a magnetic field Jc(H) than in undoped samples. The result suggests a more effective doping of carbon into the MgB2 structure and a better connectivity between the carbon-doped MgB2 grains than in previous reports. A clear correlation between the decrease in grain size and the enhancement of Hc2 was observed.

Significant enhancement of critical current density by effective carbon-doping in MgB2thin films

“…At self-field both the C-doped films show nearly comparable J c to that of pure sample. This is in contrast to the reported data on C-doped MgB 2 films, where one order of magnitude of reduction in J c was noticed at self-field and 5 K [6]. It indicates that the inter-grain connectivity for C-doped films is denser and comparable to the pure one.…”

“…The XRD patterns show only (000l) peaks of MgB 2 indicating that the films are c-axis oriented. Expansion in c-axis lattice parameter was observed with increase in carbon doping concentration, which is similar to carbon-doped films [6] but in contrast to carbon-doped single crystals, where the c-axis remains almost constant for all the carbon concentrations [8]. Compared to the undoped film, the MgB 2 (000l) peaks are suppressed as carbon concentration increases.…”

“…Despite much research done on enhancement of J c in MgB 2 bulk samples, only a little work has been reported for improving J c in MgB 2 films [5]. Few reports have shown the improvement in J c by means of carbon doping in MgB 2 films [6,7]. Here, we are reporting the effect of carbon-doping on the superconducting properties of MgB 2 thin films.…”

MgB2 coated superconducting tapes with high critical current densities fabricated by hybrid physical–chemical vapor deposition

“…Out of several dopants, carbon C [97] and carbon containing compounds, such as SiC [98], C and CaCO 3 co-addition [99] have been reported to be effective for improving the flux pinning properties of MgB 2 . Employing HPCVD technique, so far carbon has been doped in MgB 2 films, using (MeCp) 2 Mg [100] and methane [101] as the carbon source. Recently, we report the doping of Cu and Ag in MgB 2 films by two step method [102].…”

A review on the understanding and fabrication advancement of MgB2thin and thick films by HPCVD

“…Zhuang et al have improved the grain connectivity and J c by using methane (CH 4 ) as a new carbon source [91], which required adding a W filament to the HPCVD reactor to decompose it at high temperature, and the new hot-filament-assisted (HFA) HPCVD films showed both high H c2 and high in-field J c (H) compared to films doped from (MeCp) 2 [93]. The foreign phase MgB 2 C 2 was found in the TMB doped films by TEM, suggesting that only part of the carbon is doped into the MgB 2 lattice and the rest is in the carbon rich foreign phase in the grain boundaries [92].…”