Destruction of superconductivity in YBa2Cu3O/sub 7-x/ ceramics by ultrahigh magnetic field

Upper critical fields of high-T/sub c/ superconducting YBa/sub 2/Cu/sub 3/O/sub 7/ ceramics were measured in a pulsed magnetic field H/spl ap/300 T generated by magneto-cumulative plant. The presence of a superconducting phase in the cylindrical sample was detected by the appearance of S-like peculiarities on the dM/dt curve at the moment of short-time slowing of the increasing of applied magnetic field. Upper critical fields H/sub C2/ at T=4.2 and 77 K, defined in such a way, are equal to 180/spl plusmn/36 T and 48/spl plusmn/10 T accordingly.