New oxygen rich members of the 123 family of HTc superconductors

New compounds of the general composition REBa 2 Cu 3 O 6 (OH) x , 1.5 < x < 2 have been synthesized by treating the hydrogen loaded 123 compounds with oxygen. They have been characterized by X-ray diffraction, susceptibility, and NMR and NQR of Cu. The compounds are pseudocubic with the same cation sublattice as the starting 123 compounds. They are at the limit between superconductivity and antiferromagnetism and show a well defined nonsymmetric EFG at the Cu(I) sites different from the EFG tensors in the starting compounds and in samples loaded only with hydrogen