The local structural environment and oxidation state of multivalent elements in oxide glass can strongly affect their physical properties and hence, it is important to gain a detailed understanding of the factors governing their behaviour. Here, the behaviour of Fe in oxide glass matrices has been considered since iron is almost ubiquitous in practical glasses, yet its behaviour is far from fully understood. The effects of bulk glass compositions and iron concentration, and the presence of iron in multiple valences and multiple coordinations can be barriers to obtaining a detailed and quantitative understanding of its behaviour in glasses as functions of glass composition and preparation conditions. Here these barriers have been partially removed by studying Fe2+ and Fe3+, termed collectively and selective behaviour, respectively. Results from a combination of spectroscopic methods, chiefly Fe K-edge XAS, of measurements on silicate glasses doped with 0.2%mol Fe2O3 (broadly indicative of technical silicate glasses) are discussed. Whilst Fe2+ exhibits collective behaviour and can be a useful probe ion for investigating average or bulk glass structure, Fe3+ exerts strong local ordering effects, exhibiting selective behaviour, and may be less useful for probing bulk compositional effects. This local ordering of Fe3+ takes the form of a transition from [4]Fe3+ to [6]Fe3+ as functions of alkali and alkaline earth cation type. For the first time, this transition has been measured and quantified by XAS in terms of average coordination and Fe-O bond lengths and the results are consistent with the model for selective behaviour of Fe3+ ions.
