The superconducting gap structure of nanocrystalline MgB2 is investigated by heat capacity measurements. It is shown that the larger σ-gap decreases as a consequence of defects and impurities introduced by the specifics of the high-energy ball milling synthesis process. This explains the reduction of the critical temperature. The smaller π-gap slightly increases as compared to bulk MgB2 indicating an enhanced interband scattering in the nanocrystalline samples.
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