Critical Parameters of High T, Compounds

Upper critical fields of XBazCu,O,_, with X = Y, Er, Gd, Ho, Eu or Y,_,Pr, have been measured using pulsed magnetic fields up to 26T. As long as the high temperature superconductivity is present, the superconducting coherence length calculated from the critical field data, remains comparable to the size of the unit cell (-1 nm). Oxygen evolution experiments have been used to control the depletion of oxygen sites corresponding to different activation energies. The variation of the critical parameters has been determined as a function of the oxygen deficiency 6 for the YBazCu,O,., compound.