Alternating-current susceptibility measurements were performed on ternary MgB2-xCx (x = 0 to 0.1) superconducting compounds. The results were consistent with the presence of macroscopic phase inhomogeneities at extremely low levels of C doping (x ≥ 0.04) in agreement with high-resolution synchrotron X-ray powder diffraction measurements.

Phase Separation in Carbon-Doped MgB2 Studied by Means of Alternating Current Susceptibility Measurements. K.Papagelis, J.Arvanitidis, S.Margadonna, Y.Iwasa, T.Takenobu, M.Pissas, K.Prassides: Journal of Physics - Condensed Matter, 2002, 14, 7363-9