NUCLEAR RELAXATION AND Cu SPIN DYNAMICS IN YBa sub 2 Cu sub 3 O sub (6+x).

We report the sup (63) Cu NQR spectrum and nuclear relaxation rates for Cu(2) sites in sup (63) Cu- enriched YBa sub 2 Cu sub 3 O sub (6.64) (T sub c ~ 60K). The spectra reveal the presence of 3 distinct classes of Cu(2) site assumed to reflect local configurations of O vacancies in the adjacent Cu(1) layer. Nuclear spin-lattice relaxation rates exhibit a strong reduction of T sub (1T) between 100K and T sub c.