Carbon influence in the synthesis of MgB2 by a microwave method

We describe a method to produce MgB2 bulk via a microwave processing, which has not been reported yet for this material. We used two experimental arrangements, which were different in the form of the graphite thermal activator responsible for the microwave absorption. The reaction products have been analyzed from the morphological, structural and electronic point of view. The results show that the critical temperature is decreased by about 4 K when the graphite can diffuse inside the reaction cell and is incorporated in the samples, even if no evidence of carbon substitution in the MgB2 lattice is given by the lattice constants. We point out that excellent conductivity features are achieved for nearly carbon-free samples.