Temperature Dependence of the Structure and Transport Properties of Liquid Thallium

Abstract

Using a theta—theta diffractometer and quartz‐crystal monochromatized MoKα radiation, x‐ray scattering from liquidthallium has been measured as a function of temperature ranging from 350° to 700°C. The radial distribution functions (RDF) which have been obtained by Fourier inversion of the normalized intensity do not show any unusual feature and indicate a close‐packed structure for the liquidthallium. The modulation‐free part of the RDF in the region of small r where r is the radial distance suggests a high degree of reliability in the calculated value of atomic scattering factors of thallium and a considerable accuracy in the measured intensity. The interatomic distancer 1=3.30 Å of thallium does not change with temperature, and the coordination numbers change very little from 11.5 atoms at 350°C to 10.9 at 700°C. This decrease may be explained with excess‐ or free‐volume theory. The resistivity and thermoelectric power have been determined using the x‐ray interference functions and theoretically calculated values of the pseudopotential elements. The predicted values of the resistivitiesR pred are little lower than the measured values R expt1 (e.g., R pred=63 μΩ·cm, R expt1=79 μΩ·cm at 500°C). Further, the temperature coefficient of the predicted resistivities is also smaller than that of the measuredresistivities. The observed discrepancy has been attributed to the inadequacy in pseudopotential elements.