Screening charge density around severalΔZ=−1impurities in copper: Nickel, palladium, platinum, and vacancy

Using the field-cycling technique, nuclear quadrupolar couplings are measured on the neighboring shells of nickel, palladium, platinum, and monovacancy in copper. All these defects have a charge difference $\Delta Z=-1\mathrm{}$ with the host. The analysis of the results obtained on the four nearest-neighboring shells shows similar behavior, with a much larger electric-field gradient (EFG) on the first neighbors than on the following shells, but the values of the EFG are much lower around Ni than around Pd, Pt, or a vacancy. An evaluation of the contribution of the size effect shows that it can account only for a small part of the electric-field gradients, the valence effect being the main contribution in the three alloys. Additionally, an accurate value of the quadrupolar moment ratio of the copper isotopes ${}_{}{}^{63}{}_{}{}^{}\mathrm{Cu}$ and ${}_{}{}^{65}{}_{}{}^{}\mathrm{Cu}$ has been measured: $\frac{{}_{}{}^{63}{}_{}{}^{}Q}{{}_{}{}^{65}{}_{}{}^{}Q}=1.0790\mathrm{}\pm 0.0015$, and some results for $\mathrm{Cu}\mathrm{Co}$ alloys are given. This NMR technique provides a direct characterization of the monovacancy which can be very useful in the radiation damage field.