DELTA-INFLUENCE ON THE PRESSURE-EFFECT ON T-C OF HGBA2CUO4-C-RELATION(DELTA AND THE INVERSE PARABOLIC T)

We have observed a delta-independent linear pressure effect on T-c of HgBa2CuO4+delta under hydrostatic pressures up to 1.7 GPa for delta le ss than or equal to 0.30 but a nonlinear effect for delta > 0.30. Thes e results, together with previous doping data, show a possible non-rig idity of the electron bands of the compounds, based on which previous phenomenological models of the pressure effect on T-c are built, and t hus suggest only a restricted universality for the inverse parabolic r elation between T-c and charge carriers per CuO2-layer. In other words , factors in addition to charge carriers can affect high temperature s uperconductivity.