High-pressure in situ studies at up to 1.0GPa were made of high-pressure synthesized MgB2. The as-prepared samples were of high quality in terms of a sharp TC at 39K. The in situ high-pressure measurements were carried out by using a Be-Cu piston-cylinder-type instrument with mixed oil as the pressure transmitting medium. This produced a quasi-hydrostatic pressure environment at low temperatures. The superconducting transitions were measured by using the electrical conductance method. It was found that TC increased by more than 1K with pressure in the low-pressure range, before the TC value decreased with further increases in pressure.

Enhanced MgB2 Superconductivity Under High Pressure. Z.X.Liu, C.Q.Jin, J.Y.You, S.Li, J.L.Zhu, R.C.Yu, F.Y.Li: Chinese Physics Letters, 2002, 19, 120-1