Atomic Distribution and Electrical Properties of Liquid Mercury—Thallium Alloys

Abstract

The x-ray-diffraction patterns of liquid binary Hg–Tl alloys have been measured using a theta—theta diffractometer and quartz crystal monochromatized Mo Kα radiation. Pure mercury and five alloys of 5, 8.5, 16, 28.6, and 40 at. % thallium were studied at room temperature (25°C), whereas pure thallium was studied at 350°C. Since mercury and thallium are next to each other in the periodic table, the contribution of the Laue monotonic scattering to the scattered intensity should be negligible. The radial distribution functions were refined by an error-analysis program and then the refined interference functions were computed and used to calculate the electron transport properties of the alloys. The general equation for the scattering cross section of the electrons in liquid metals has been used and expressed in terms of the matrix elements of the pseudopotentials and the interference functions of the respective elements. Assuming that the atomic distribution is random, the resistivity and thermoelectric power of the alloys and the pure elements were calculated. There is some disagreement between the calculated or predicted and measured values of the resistivity. The predicted value of resistivity of mercury and thallium are 30 and 60 μΩ·cm, respectively. The interatomic distances were found to vary linearly from 3.05 for pure Hg to 3.28 Å for Hg−40 Tl alloy. The value for pure Tl is 3.30 Å. This linear variation is not in agreement with previous results. The positive deviation from Vegard's law has been attributed to the electrochemical and valence difference of the two elements. The behavior of the coordination number with concentration, the change being from 10.0 to 11.5 for pure Hg to pure Tl, is similar to that of the interatomic distance with the concentration.