Cu nuclear quadrupole resonance of YBa2Cu3O/sub x/ with varying oxygen content

/sup 63/Cu and /sup 65/Cu nuclear quadrupole resonance (NQR) results of eleven YBa2Cu3O/sub x/ samples with x ranging from 7.00 to 6.00 are reported. All measurements were done at room temperature. An attempt was made to quantify integrated signal intensities. The spin-lattice relaxation times (T1) were either shorter than 0.3 ms or longer than 60 ms. Because the short relaxation times are interpreted as arising from the interaction with conduction electrons, the T1's could be used to distinguish between metallic and nonconducting substructures. In the 7.0<x<6.9 range where T/sub c/ = 90 K, the shapes of the NQR spectra were independent of x, but their overall intensity decreased with decreasing oxygen content. In the intermediate range, 6.8<x<6.4 where T/sub c/ = 55 K, narrow peaks due to nonconducting substructures were observed together with a distinctive short-T1 line shape, indicating that the (super)conducting state with this oxygen stoichiometry is essentially different from that at x = 7. This short-T1 signal was more pronounced in low-temperature annealed samples for which a T/sub c/ of 55 K was observed over a larger x range. It is shown to be consistent with a superordered structure of oxygen vacancies in the conducting substructures. No metallic sites were found for x<6.3 where T/sub c/∼0. A total of six Cu resonance frequencies were identified between 20 and 32 MHz, some of which could be assigned to specific local crystal structures. In several instances, when the oxygen content was lowered, an NQR peak due to metallic Cu was replaced by a nonmetallic signal at the same frequency