The influence of various dopants on the properties and local structure of glass samples was explored and a quantitative determination of the structural changes in the network as the dopant concentration was varied was achieved using 27Al, 29Si, 33S MAS NMR.\ud \ud Findings showed that silver- and copper-doping of phosphate based glass gave rise to unexpected connectivity between the phosphate units most likely due to some phase separation creating a different composition to that intended in the majority glass. This emphasises the importance of a careful and systematic approach to sample manufacture in achieving high sample stabilities, leading to a good degree of predictability in both structure and properties.\ud \ud Lanthanum and yttrium ions, despite their huge difference in ionic size, showed very little difference in their effect upon the phosphate coordination in the glass samples as they remain outside the phosphate network, cross-linking between the terminal oxygen atoms. The aluminium ions however, showed evidence of behaving in both a cross-linking manner and in a network forming, tetrahedral role and it appears energetically favourable for them to avoid any Al-O-Al linkage, hence resulting in the formation of AlO4 rather than exceeding the AlO5 or AlO6 quantities that would lead to this. The sulphur NMR looks to be a very promising method for future use in understanding sulphur speciation in glasses
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