The Science & Technology
of Glass
Cambridge - Monday 4th to
Wednesday 6th September 2017



Alex Hannon
<alex.hannon@outlook.com>

article posted 25 Apr 2017

Alex Hannon:

I am employed at the ISIS Facility of the Rutherford Appleton Laboratory, where I am responsible for the neutron diffractometer GEM (GEneral Materials). I am responsible for experiments on GEM to study the structure of glasses, liquids and disordered crystals.

My personal research is into the structure of oxide glasses, such as germanate glasses, and chalcogenide glasses, such as arsenic sulphide glasses. As well as developing general techniques for studying glasses by neutron diffraction, I have particular interests in studies of bonding in glasses, and the variation of coordination numbers with composition.

I am an editor of the Society's journal Physics and Chemistry of Glasses, and I am the chairman of the international organising committee of the International Conference on Borate Glasses, Crystals, and Melts.


Bond valence analysis of phosphate structures
Alex C. Hannon

ISIS Facility, Rutherford Appleton Laboratory, Chilton,
Didcot, Oxon OX11 0QX, UK.


The bond valence method is very powerful for structural analysis of both crystals(1) and glasses,(2) and it accounts for the correlation between bond length and coordination number. Phosphate materials, however, are more challenging than most oxides for bond valence analysis, due to the unusually large range in valence of the P O bonds. These range from true terminal double P=O bonds in pure P2O5, to bridging P-O bonds in phosphates with relatively high P2O5 content, where neighbouring modifier cations reduce the valence of the bonds to less than one. I report the modification of the standard bond valence expression to account better for the lengths of P-O bonds in phosphates, and apply the result to the consideration of oxygen environments and M O bonding (M=modifier cation) in phosphate glasses.

References:

1. Brese, N. E. & O'Keeffe, M. Acta Cryst. B, 1991, 47, 192.

2. Hannon, A. C. J. Non-Cryst. Solids, 2016, 451, 56.