The influence of lattice strain and Mg vacancies upon the superconducting properties was investigated. High-quality samples with sharp superconducting transitions were prepared. The variations in lattice strain and Mg vacancy concentrations were obtained by varying the synthesis conditions. It was found that a high strain (about 1%) and the presence of about 5% of Mg vacancies resulted in a lowering of TC by only 2K.

Effect of Lattice Strain and Defects on the Superconductivity of MgB2. A.Serquis, Y.T.Zhu, E.J.Peterson, J.Y.Coulter, D.E.Peterson, F.M.Mueller: Applied Physics Letters, 2001, 79[26], 4399-401