The intensities of the 63Cu nuclear quadrupole resonance and quadrupolar-satellite nuclear magnetic resonance at high temperatures were determined for the planar Cu(2) sites. It was observed that the spin-echo intensities decreased markedly between room temperature and 500K, and that the onset of intensity-loss occurred at lower temperatures in more defective samples. Measurements of the spin-echo decay rates revealed that the intensity loss was associated with a loss of phase coherence which exceeded that which was expected for spin-spin and spin-lattice relaxation. By using simple models, these effects could be attributed to changes, in the local atomic environment, which were presumed to be caused by the motion of O atoms in the Cu(1) layer. These motions occurred over a time-scale which was of the order of 10μs at 500K. Their probability was enhanced, at lower temperatures, by the presence of structural defects.

S.P.Klein, R.P.Wang, A.W.Sleight, W.W.Warren: Physical Review B, 1997, 56[10], 6335-42