In a new paper, recently published in the prestigious journal Proceedings of the National Academy of Science USA (PNAS), scientists from the University analysed work carried out at leading neutron and x-ray diffraction centres, like the Institut Laue-Langevin and ISIS.
This work shows how under ambient conditions oxide glasses have an open structure, however under high pressure conditions the collapse of their atomic arrangement brings the oxygen atoms closer together. In time, the packing of oxygen creates important changes in the network structure – something which in turn affects the material’s compressibility and viscosity.
Their analysis confirmed that the overall network structures and associated physical properties of a wide variety of disordered oxides can be categorised and therefore predicated by the material's oxygen-packing fraction (the volume in a liquid or glass structure that is occupied by oxygen atoms) which increases under pressure. This challenges previous suggestions that the oxygen number density (the number of atoms in a given volume) on its own could provide the best indication of structural change.
By understanding more about the properties of high-density liquids to aid in the design of glass, this work has the potential to develop new techniques using pressure to make glasses with novel properties.
Professor Phil Salmon explained: “Up to now there has been no reliable guide for predicting the conditions under which transformations occur. However, if you have got a material and you know that the packing density is approaching the random close-packing upper limit, where 64 per cent of the volume is taken up with oxygen, it is a strong indication that you are going to get a change in structure and therefore a change in the physical properties.”
John Mauro, Manager of Glass Research at Corning Incorporated, the world’s leading manufacturer of speciality glass and ceramics added: “Most importantly, Professor Salmon and his co-workers have made the link to the topology of the glass network, which is what governs many of the macroscopic properties of the glass. These insights will be very helpful if we wish to design new glasses under high pressure conditions.”
There is also interest in this work from the geoscience community, including colleagues at Bristol University. As a result of the sensitivity of oxygen atoms to their surrounding environments, and the impact that structural changes have on a material’s bulk properties, the researchers believe this packing analysis could be used to gauge the conditions materials experienced during their formation.
To find out more and access a copy of the paper ‘Packing and the structural transformations in liquid and amorphous oxides from ambient to extreme conditions’ published in PNAS see http://www.pnas.org/content/111/28/10045 .
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