EXAFS studies of molten ZnCl₂, RbCl and Rb₂ZnCl₄

Abstract

The local structures of molten ZnCl2, RbCl and Rb2ZnCl4 are measured with the EXAFS technique. Several models are used to analyse the data, and some structural parameters as well as the radial distribution functions of the nearest-neighbour atoms around Zn or Rb atoms are obtained. The tetrahedra consisting of four Cl atoms around Zn are found to be dominant and stable in molten ZnCl2. The skewed behaviour of the radial distribution function for Rb-Cl in molten RbCl is also found, while the local structures around Rb can be regarded as a persistence of the solid state but with strong short-range disorder. In molten Rb2ZnCl4, a network linked by Zn Cl4 groups is not found and the nearest-neighbour structures around Rb atoms are more disordered than in molten RbCl. This has also confirmed that the EXAFS method can provide reliable information about the nearest-neighbour atom-atom coordination for some molten salts, which is helpful in specifying the painwise interaction potential.

High temperature–high pressure apparatus for neutron diffraction on molten salts: Structure factors of molten zinc chloride

“…This confirms the assumption that the structure of the ZnCl 4 tetrahedra undergo no fundamental changes with increasing pressure. The positions of the first maxima (217 pm) are slightly smaller than the values determined in earlier investigations [6][7][8][9][10][11][12][13][14] (230 pm), which is not surprising with regard to our restricted k-range. The coordination numbers of the first maxima, calculated by fits with Gaussians, is about four in the whole investigated density range, and therefore in good agreement with the ZnCl 4 tetrahedra model.…”

“…This indicates that the structure building units are not changed fundamentally in molten zinc chloride even under high pressure. In the case of molten zinc chloride at normal pressure various investigations [6][7][8][9][10][11][12][13][14] identified these units as ZnCl 4 tetrahedra. Therefore it can be supposed that molten zinc chloride under pressures up to 4000 bar is still built up from ZnCl 4 tetrahedra of similar Fig.…”

“…The (5). The high temperatures are produced by three heaters (cylinder of brass wound around with wire) (6), while the Bridgman seals are protected by two efficient water cooling jackets (7). In the course of our tests it turned out that a small amount of helium with a pressure of 1-2 mbar inside the aluminium bell-jar (2) improves the temperature regulation without any influence on the scattering properties.…”

“…The transport properties show an anomalous behavior, which probably can be explained by structural changes. Various investigation methods like EXAFS, 6,7 X-ray 8,9 and neutron scattering [10][11][12][13][14] were applied to molten zinc chloride at normal pressure in order to explore its structure. In the case of neutron scattering, Biggin and Enderby 10 were able to determine the partial atom pair correlation functions of liquid zinc chloride at 600 K by 35 Cl/ 37 Cl isotopic substitution neutron experiment.…”

Radiation-Assisted Formation of Metal Nanoparticles in Molten Salts

“…Synchrotron-based X-ray radiation with tunable energy is an attractive choice as it can, on one hand, initiate the reduction of metal ions and, on the other hand, probe the local structure of metal nanoparticles that may form as a result. Extended X-ray absorption fine structure (EXAFS) and X-ray absorption near-edge structure (XANES) are element-specific techniques that can interrogate the local environment of metal species in molten salts under high-temperature conditions. − EXAFS probes short-range structural order and provides direct information on coordination number, interatomic distance and amount of disorder, while XANES gives the chemical structure and oxidation states in the local environment of the absorber. A recent work reported an XAFS study of [BMIM]­[AuCl 4 ] ionic liquid in which the formation of Au–Au bonds was facilitated by solvated electrons generated as a result of X-ray irradiation .…”