The structure and properties of anhydrous, alkali ultra-phosphate glasses
Binary alkali phosphate glasses have been studied for some time. However, research has largely concentrated on glasses where the alkali oxide fraction is greater than 0.5. Such glasses are easy to prepare, strongly glass forming, and moderately stable against hydration. Glasses with less than 50 mole% alkali oxide, ultra-phosphates, have received almost no attention, presumably due to the moisture sensitivity and vapor pressure near melting of ultra-phosphate materials. With the development of novel glass preparation techniques, such problems have been overcome enabling a thorough investigation of the sodium and lithium ultra-phosphate glass systems. Specifically, this research describes the short range order and the compositional dependence of the properties of binary alkali ultra-phosphate glasses. In this way, one of the first complete structure-property correlation maps for alkali ultra-phosphate glasses was developed;The physical properties of both the sodium and lithium ultra-phosphate glass systems show a sharp break at 20 mole% alkali which cannot be described by a chemically simple model of the glass structure. Alternatively, changes in oxygen bonding are responsible for the anomalous property trends. Also, properties were found to be dependent on melt-processing at temperatures far above T g. Results suggest the formation of large, slowly relaxing structures are responsible for such melt-processing dependence. In addition to exploring structure-property relationships, the structural relaxation dynamics of the alkali ultra-phosphate glasses were explored. Vitreous P2O5 is found not to be the 'archetypal' strong liquid, but is an intermediate liquid having a distribution of relaxation times, T g and heat capacity commensurate with such a liquid.