Percolative Superconductivity in Mg1-xB2

Using various synthesis techniques, we have obtained a number of interesting results regarding the magnesium diboride system. First, we have observed a maximum T_C of 42 K in Mg_1-xB₂ films on crystalline boron substrates, which is significantly higher than the reported value of 39 K. Furthermore, our study of Mg-vacant Mg_1-xB₂ specimens, fabricated by using high-pressure (35 MPa) sintering, provides convincing evidence for electronic phase separation, probably induced by Mg-vacancy clustering.