Systematical trends of nuclear quadrupolar relaxation in metallic liquid alloys of indium

Applying the method of perturbed angular distributions following the nuclear reaction ${}_{}{}^{115}{}_{}{}^{}\mathrm{In}(\alpha ,2n){}_{}{}^{117}{}_{}{}^{}\mathrm{Sb}_{}^m{}_{}{}^{}$, systematic measurements have been made of the nuclear-quadrupolar relaxation rate $R_Q$ for ${}_{}{}^{117}{}_{}{}^{}\mathrm{Sb}_{}^m{}_{}{}^{}$ probe nuclei in liquid alloys of In, as a function of various parameters: the dependence of the rate enhancement on the partner element is established in 14 equicomposition alloys with $\mathrm{I}b$, $\mathrm{II}b$, $\mathrm{II}a$, $\mathrm{IV}a$, and $\mathrm{V}a$ group elements. The composition dependence of the rate in the In-rich domain has been recorded for ${\mathrm{In}}_C{X}_{1-C}$, $X=\mathrm{A}\mathrm{u},\mathrm{H}\mathrm{g},\mathrm{A}\mathrm{s},\mathrm{a}\mathrm{n}\mathrm{d}\mathrm{B}\mathrm{i}$, and the temperature dependence of the rate is presented for ${\mathrm{In}}_{0.5}$ ${\mathrm{Bi}}_{0.5}$ and ${\mathrm{In}}_{0.5}$ ${\mathrm{Hg}}_{0.5}$. On the average we find a correlation of the rate enhancement to the valence difference between In and the partner element. The composition dependence confirms the characteristic deviation from a simple substitutional behavior described by a $C(1-C)\mathrm{}$ rule which has been found in earlier NMR work. The temperature dependence of the rate in ${\mathrm{In}}_{0.5}{X}_{0.5}$ alloys with enhancement, can be parametrized by an Arrhenius law where the activation energy is roughly a linear function of the alloy melting temperature; the proportionality factor, however, is about one half the factor occuring in diffusion. These results are examined in the frame of the Sholl and Warren theory for quadrupolar relaxation which we extend to alloys in its general form in terms of partial-dynamical structure factors taking advantage of analogies in the formulation of electrical resistivity. It is concluded from an evaluation of the formulas based upon a hard-sphere model that quadrupolar relaxation must be governed by the long-wavelength part of the structure factors. More specifically quadrupolar relaxation seems to be sensitive to the wave-number interval between the thermodynamical limit and the main peak of the static-pair correlation function of the liquid, a region which is poorly explored by other experimental techniques.