Phase separation in carbon-doped MgB₂ studied by means of alternating current susceptibility measurements

The phase purity and/or possible phase inhomogeneities in the MgB_2-xC_x (0≤x≤0.1) ternaries were examined. The investigations were done by carrying out ac susceptibility measurements at different ac amplitudes and dc magnetic fields as a function of temperature. The samples were prepared by heating mixed powders of amorphous boron, carbon black and magnesium. Absence of weak links were confirmed by the linear dependence of the ac susceptibility on the amplitude and frequency of the applied ac field. No peak characteristic of intergranular losses was found at low temperatures in the imagery part of the ac susceptibility.