1. Department of Physics, University of Bath, Bath BA2 7AY, UK
2. HH Wills Physics Laboratory, Royal Fort, University of Bristol, Bristol, BS8 1TL, UK
3. Institut Laue-Langevin, BP 156, F-38042, Grenoble Cédex 9, France
4. *Present address: Department of Food Science, Stocking Hall, Cornell University, Ithaca, New York 14853, USA

Correspondence to: Philip S. Salmon¹ Correspondence and requests for materials should be addressed to P.S.S. (Email: p.s.salmon@bath.ac.uk).

Abstract

Atomic ordering in network glasses on length scales longer than nearest-neighbour length scales has long been a source of controversy^{1, 2, 3, 4, 5, 6}. Detailed experimental information is therefore necessary to understand both the network properties and the fundamentals of glass formation. Here we address the problem by investigating topological and chemical ordering in structurally disordered AX₂ systems by applying the method of isotopic substitution in neutron diffraction to glassy ZnCl₂. This system may be regarded as a prototypical ionic network forming glass, provided that ion polarization effects are taken into account⁷, and has thus been the focus of much attention^{8, 9, 10, 11, 12, 13, 14}. By experiment, we show that both the topological and chemical ordering are described by two length scales at distances greater than nearest-neighbour length scales. One of these is associated with the intermediate range, as manifested by the appearance in the measured diffraction patterns of a first sharp diffraction peak at 1.09(3) Å^-1; the other is associated with an extended range, which shows ordering in the glass out to 62(4) Å. We also find that these general features are characteristic of glassy GeSe₂, a prototypical covalently bonded network material^{15, 16}. The results therefore offer structural insight into those length scales that determine many important aspects of supercooled liquid and glass phenomenology¹¹.

1. Department of Physics, University of Bath, Bath BA2 7AY, UK
2. HH Wills Physics Laboratory, Royal Fort, University of Bristol, Bristol, BS8 1TL, UK
3. Institut Laue-Langevin, BP 156, F-38042, Grenoble Cédex 9, France
4. *Present address: Department of Food Science, Stocking Hall, Cornell University, Ithaca, New York 14853, USA

Correspondence to: Philip S. Salmon¹ Correspondence and requests for materials should be addressed to P.S.S. (Email: p.s.salmon@bath.ac.uk).

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