Structural studies of metal doped phosphate glasses and computational developments in diffraction analysis

The thesis focuses on the analysis and determination of the structure of various metal

doped phosphate glasses, which are of interest for their potential biomedical properties.

The structures have been determined principally by X-ray and neutron diffraction but

are also supported by complimentary X-ray absorption spectroscopy measurements

and computational modelling. Such studies contribute to about half of the work

presented in this thesis.

Among the glasses of interest are silver-doped calcium sodium phosphates, which

exhibit antimicrobial properties when the Ag+ ions are released over time in an

aqueous environment. The advanced probe technique of neutron diffraction with

isotropic substitution (NDIS) has been applied to elucidate the structural role of silver

in these glasses. The results revealed that silver occupies a highly distorted octahedral

environment analogous to that in crystalline Ag2SO4.

Another glass study herein is associated with zinc titanium calcium sodium phosphate,

which is biomedically interesting since the release of Zn2+ ions is shown to enhance

cell attachment and proliferation. Structural analysis of multi-component glasses such

as these tends to be difficult, but diffraction techniques and X-ray absorption

spectroscopy have been used together to reveal the cation first neighbour coordination

environments.

The other significant element of the work presented here has been the development of

data analysis techniques, with the emphasis on the creation of a program, which allows

co-fitting of X-ray and neutron diffraction data of amorphous (and potentially

crystalline) data. The code is written in MATLAB and makes use of the Nelder-Mead

simplex method to minimise a set of “best guess” structural parameters supplied by the

user. Extrema bound constraints are implemented by means of a sinusoidal parameter

transform. Ultimately, the code is to be compiled and made available to users via the

ISIS Pulsed Neutron Facility, UK.