Letter | Published:

Ionic structure in aqueous electrolyte solution by the difference method of X-ray diffraction

Naturevolume 321pages5253 (1986) | Download Citation



Neutron diffraction difference methods based on isotopic substitutions offer a means of directly probing the detailed structure around a solute dissolved in a host solvent1, but there are two main drawbacks to their implementation. First, they rely on the use of separated isotopes which are expensive and sometimes of limited availability. Second, the experiments have to be performed at a sophisticated central facility to obtain sufficiently intense beams of thermal neutrons. We have therefore initiated a series of experiments aimed at introducing difference methods to X-ray diffraction studies of liquid and amorphous systems. Difference methods have been attempted before2, but the absence of definitive neutron data did not allow the method to be made fully quantiative. We now present the first results obtained from such a study in which the difference technique is applied to a concentrated aqueous electrolyte solution and the cation–cation distribution function gMM(r) is determined directly. The success of the method rests on the ability to identify nearly isomorphic pairs of elements, whose isomorphism can be quantified by reference to similar results obtained from the first-order difference method of neutron diffraction3.

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    • S. Cummings

    Present address: Shuster Laboratory, University of Manchester, M137PL, UK

    • J. E. Enderby

    Present address: Institute Laue Langevin, BP 156X, 38042, Grenoble Cedex, France


  1. H. H. Wills Physics Laboratory, University of Bristol, Bristol, BS8 1TL, UK

    • N. T. Skipper
    • , S. Cummings
    • , G. W. Neilson
    •  & J. E. Enderby


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