Electric field gradients and impurity distributions in doped noble metals: A systematic study

The electric field gradients created at ${}_{}{}^{111}{}_{}{}^{}\mathrm{Cd}$ nuclei by dilute transition-element impurities in noble metals are studied by the technique of time-differential perturbed angular correlation. The present results supplement previous ones with data for the alloys $\mathrm{Cu}\mathrm{Rh}$, $\mathrm{Cu}\mathrm{Pt}$, $\mathrm{Ag}\mathrm{Rh}$, $\mathrm{Ag}\mathrm{Ir}$, $\mathrm{Au}\mathrm{Rh}$, $\mathrm{Au}\mathrm{Pd}$, and $\mathrm{Au}\mathrm{Pt}$, including temperature and concentration dependence in some typical cases. The results show conclusively that, for most impurities situated to the left of the host noble metals in the Periodic Table, there is a strong attraction between the probe In and the impurity atoms. The binding energy $\Delta E_B$ for the probe-impurity system is measured for the $\mathrm{Cu}\mathrm{Rh}$ and $\mathrm{Cu}\mathrm{Pt}$ alloys. The temperature dependence of the high-frequency quadrupole interaction ${\nu }_h$ due to a single-impurity nearest neighbor to the probe is found to obey the usual empirical law $\nu \mathrm{}\left(T\right)=\nu \mathrm{}\left(0\right)(1-\alpha T^{\frac{3}{2}})$. The wealth of experimental data thus made available allows a systematic examination of the results from which the following facts emerge: (i) The observed high frequency ${\nu }_h$ is related to the nominal valence difference $\Delta Z$ between impurity and host and to a parameter $\lambda$, the difference in the period of impurity and host in the Periodic Table: (ii) a correlation of $\Delta E_B$ with both $\Delta Z$ and $\lambda$ is apparent: and (iii) an inverse correlation between the $\alpha$ parameter and $\Delta E_B$ is apparent.