DETECTION OF COPPER PRECIPITATES IN CU2O BY NMR

Weak **6**3Cu NMR signals characteristic of metallic copper have been found in three type-C Cu//2O crystals, but not in types A and B. This is in accordance with presently accepted models of these materials. The resonances are asymmetric in two of the three crystals. One shows skin-depth effects, implying particle size APP GRTH 23 mu m, the other shows some second-order quadrupole broadening, presumably associated with strains or surface effects. From the areas under the absorption curves, mass concentrations of copper precipitates ranging from 0. 023 to 0. 034% are deduced. However, the smallest value is found from an asymmetric resonance where significant loss of signal must have occurred. The data are not inconsistent with a concentration of about 0. 034% for all three crystals. For type-A and -B material, an upper limit of 3-7 ppm can be placed on the concentration, depending on the assumed contribution of the satellites to the resonance. **6**3Cu resonances associated with the transitions between Zeeman-split plus or minus one-half quadrupole states in Cu//2O were troublesome, since they overlapped the metal resonance at many sample orientations. Strong Cu//2O signals, observed at one orientation, indicated that part of the crystal must have grown with left brace 111 right brace faces.