The pressure dependence of the superconducting transition temperature from 0 to 4.5GPa was investigated by using a diamond-anvil cell. It was found that, under a non-hydrostatic pressure, TC at first decreased linearly at a rate dTC/dP = -1.1K/GPa from 0 to 0.5GPa. However, as the pressure was increased from 0.5 to 1.3GPa, dTC/dP decreased sharply; passing through a small minimum and then starting to increase at about 1.3GPa. At this pressure, TC increased slightly. From about 1.4 to 4.5GPa, TC, decreased with a subsequent quadratic, as opposed to the expected linear, dependence upon P.

Anomalous Non-Linear Pressure Dependence of TC for MgB2. R.Falconi, A.Durán, R.Escudero: Journal of Physics - Condensed Matter, 2002, 14, 3663-7