Anomalous temperature behavior of Sn impurities

Abstract

Sn impurities in Pb and Ag hosts have been investigated by Mossbauer effect and in Pb by x-rayabsorption fine-structure (XAFS) studies. The Sn atoms are dissolved up to at least 2 at. %%u o inP ban dup to at least 8 at. % in Ag for the temperature ranges investigated. The concentration limit for Sn-Sn interactions is 1 at. % for Pb and 2 at. % for Ag as determined experimentally by lowering the Sn concentration until no appreciable change occurs in the Mossbauer effect. XAFS measurements verify that the Sn impurities in Pb are dissolved and predominantly at substitutional sites. For both hosts the temperature dependence of the spectral intensities of isolated Sn impurities below a temperature To is as expected for vibrating about a lattice site. Above To the Mossbauer spectral intensity exhibits a greatly increased rate of drop-off with temperature without appreciable broadening. This drop-off is too steep to be explained by ordinary anharmonic effects and can be explained by a liquidlike rapid hopping of the Sn, localized about a lattice site. Higher-entropy-density regions of radii somewhat more than an atomic spacing surround such impurities, and can act as nucleation sites for three-dimensional melting.

Observation of rapid atomic motion in solid 3 He- 4 He mixtures using NMR

“…That of course is true if the vacancy is treated as a point-like static perturbation of the lattice. Now, ours and other studies [16], [17] indicate each vacancy is responsible for fluid-like behaviour in its vicinity. For the range of 3 He densities used in our work, we can estimate the linear dimension of the "sphere of influence" of a vacancy at 10-20 Å.…”

“…Finally, we address the broader scope of our observations. Recently, Haskel et al [16] detected the onset of rapid motion of Sn impurities in solid Pb at temperatures as low as 300 K below melting. A similar effect was observed by Rousseau et al in an NMR experiment on an organic solid [17].…”

Anomalous concentration dependence of the Mössbauer isomer shift of Ag-Sn alloys

“…In previous reports [17,18] we described some dynamical properties of Sn impurities in Pb and Ag hosts: in particular, in figure 5 of reference [17] we reported on the temperature dependence of the LS for 2.0, 4.0 and 8.0 at.% Sn in a Ag host; all of the concentrations were below the limit of Sn solubility in Ag (≈11.3 at.% at 724 • C and 9.35 at.% at 218 • C [19]). Anomalous behaviour in the LS can be seen in figure 5 (reference [17]) for samples with 4.0 and 8.0 at.% Sn in Ag.…”

“…In previous reports [17,18] we described some dynamical properties of Sn impurities in Pb and Ag hosts: in particular, in figure 5 of reference [17] we reported on the temperature dependence of the LS for 2.0, 4.0 and 8.0 at.% Sn in a Ag host; all of the concentrations were below the limit of Sn solubility in Ag (≈11.3 at.% at 724 • C and 9.35 at.% at 218 • C [19]). Anomalous behaviour in the LS can be seen in figure 5 (reference [17]) for samples with 4.0 and 8.0 at.% Sn in Ag. It is manifested, for virgin samples, in a deviation of the slope from the expected value given by equation ( 2), together with a rather sharp increase in IS at about T ≈ 520 K. The anomalous deviation in slope disappears after the first heating-cooling cycle while the change in IS at T ≈ 520 K, as detailed below, persists and is independent of the thermal history of the sample.…”

“…Attempts to fit more than one Lorentzian resulted in poorer fits. For evaluation of the effective absorber thickness we used a procedure described before [17]. Extrapolation to zero thickness gives an absorber linewidth of a = 0.44 mm s −1 .…”