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Advanced Structural Characterisation Techniques for Amorphous Materials: Case Study of Rare-earth Phosphate Glasses

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This seminar concerns the structural characterisation of rare-earth phosphate glasses, materials that exhibit exotic optical and magnetic properties. The high structural complexity of glasses and their highly disordered nature means that little structural information can be gained from employing just one structural characterisation technique. We have therefore used a wide range of structural probes, conventional and anomalous X-ray and neutron diffraction [1,2], rare-earth LIII and K-edge EXAFS [3,4], XANES [5], solid-state NMR [1,2], FTIR [6], each of which reveal particular key structural information about the glasses, which when pieced together and combined with theoretical modelling techniques (e.g. Reverse Monte Carlo routines), allow the realisation of an overall unified three-dimensional model of these glasses. To date, we have characterised the pair-wise structural correlations in these glasses out to a radial distribution of 4A, and this is described in the introduction of the presentation. However, one key atomic pair-wise correlation, the closest R…R separation, has proved particularly difficult to characterise, and yet is of key importance from a materials-centred perspective, given that this separation dictates the optical and magnetic properties in these glasses. Attempts to combat this have led us to undertake some complicated and novel experiments. We report herein the descriptions and results of three such experiments: the world’s first successful magnetic difference neutron diffraction experiment on an amorphous material, using the GEM powder neutron diffraction instrument at ISIS , RAL; the first example of a full anomalous neutron scattering experiment, accessing both real and imaginary component differences, where data was collected on D4 at the ILL , Grenoble, France; and an anomalous X-ray scattering experiment, undertaken on 1-ID, APS , USA. Results are presented and are shown to have important implications on their physical properties.

References

1. J. M. Cole, E. R. H. van Eck, G. Mountjoy, R. J. Newport, T. Brennan, G. A. Saunders (1999). J. Phys. Cond. Matt., 11, 9165-9178.

2. J. M. Cole, E. R. H. van Eck, G. Mountjoy, R. Anderson, T. Brennan, G. Bushnell-Wye, R. J. Newport, G. A. Saunders (2001). J. Phys. Cond. Matt., 13, 4105-4122.

3. R. Anderson, T. Brennan, J. M. Cole, G. Mountjoy, D. M. Pickup, R. J. Newport, G. A. Saunders, (1999). J. Mater. Res. 14, 4706-4714.

4. J. M. Cole, A. C. Hannon, R. A. Martin, R. J. Newport, “Direct observation of R…R distances in rare-earth® phosphate glasses by magnetic difference neutron diffraction”, Phys. Rev. B. 73 (2006) 104210-(1-5).

5. J. M. Cole, A. C. Wright, R. J. Newport, C.E. Fisher, S. J. Clarke, R. N. Sinclair, H. E. Fisher, G. J. Cuello, “The structure of the rare-earth phosphate glass, (Sm2O3)0.205(P2O5)0.795 studied by anomalous dispersion neutron diffraction”, J. Phys. Cond. Matt. 19 (2007) 056002(1-12).

6. J. M. Cole, R. J. Newport, “Direct observation of the R…R separation in rare-earth phosphate glasses”, J. Non-Cryst. Solids 353 (2007) 1773-1778.

This talk is part of the Mineral Sciences Seminars series.

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