PHASE-SEPARATION IN HYDROGEN-LOADED 123 AND 124 COMPOUNDS OBSERVED BYCU NMR AND NQR

The transition from superconducting to antiferromagnetic behavior in R E Ba2Cu3O7H(x), RE = Y, Gd, has been studied by Cu NMR and NQR. In the Gd compounds the spectra of Cu(1) and Cu(2) sites could be separated by the strong relaxation induced by the magnetic moments of Gd on the neighboring Cu(2) sites. Already at small x of about 0.4, antiferromag netic Cu(2) sites are revealed by an AF-NMR spectrum. At the same x we find a strong broadening of the normal NQR spectrum and a new sharp l ine at 27 MHz for Cu-63, indicating a new EFG of the Cu(1) sites in th e AF phase. The transformation to the AF state is complete at about x = 2.0. Annealing of the doped material at 350-degrees-C leads to the n ormal oxygen-depleted 123 compounds, proving that the cation lattice i s not distorted even at high x. As in the case of the pure YBCO, no st atic magnetic moments exist at the Cu(1) sites of the hydrogen-contain ing phase. Hydrogen addition is found to produce a similar antiferroma gnetic spectrum in 124 material.