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Raman spectroscopy is employed to study both the strain and the carbon substitution level in SiC-doped MgB2 bulk samples. Raman spectroscopy was demonstrated to be a better method to distinguish the individual influences of strain and carbon than standard X-ray diffraction. It is found that the lattice parameter correlation method for C content determination is invalid for highly strained samples. Our result also provides an alternative explanation for lattice variation in non-carbon-doped MgB2, which is basically due to lattice strain. [ABSTRACT FROM AUTHOR]

Abstract: We studied the effects of MgB2 with embedded multiwall carbon nanotubes (MWCNTs) on the crystallinity, lattice parameters, critical current density (J c), upper critical field (H c2), irreversibility field (H irr), and microstructure of MgB2. Fe sheathed un-doped and MWCNT doped MgB2 wires were fabricated by the powder-in-tube (PIT) method and sintered at the high sintering temperatures of 900°C. We observed that for the MWCNT doped sample high temperature sintering resulted in depressed crystallinity, shrinkage of the a-lattice parameter, higher J c up to 12T, and lower critical temperature (T c) values. Specifically, MWCNT doped samples sintered at 900°C exhibited excellent J c, ∼104 Acm−2 up to 9T at 4.2K. This can be explained by lattice distortion and poor crystallinity due to carbon (C) substitution from the MWCNT. [Copyright &y& Elsevier]

Abstract: We have investigated the effect of nano-carbon doping on phase formation, critical current density, flux pinning and irreversibility field in MgB2−x bulk sample where x =0, 0.05, 0.1, 0.2 and 0.3. XRD results showed a systematic shift of lattice parameter a, which is attributed to carbon substitution, while the lattice parameter c almost did not change as the carbon content increased. Enhancement of magnetic J c by two orders at 5K and 8T was observed for the sample of x =0.1, as the J c(H) reached the value of >104 at 8T. In addition, the H irr of the 5% doped carbon was enhanced from 4.9T to 5.8T as compared to the undoped sample. Boron substitution for carbon is proposed to be responsible for the enhancement of flux pinning. [Copyright &y& Elsevier]