Rare‐earth titanate melt structure and glass formation

Abstract

AbstractThe structure of rare‐earth titanate melts and glasses of composition 17RE2O3.83TiO2 have been investigated in situ by aerodynamic levitation with laser heating. Ti K‐edge X‐ray absorption near‐edge structure (XANES) spectroscopy reveals an effect of RE cation size on mean Ti‐O coordination numbers (nTiO), which increase from ∼4.8(2) in glass‐forming La titanate to ∼5.1(2) in non‐glass‐forming Sc titanate liquids. We suggest that the associated increase in OTi3 triclusters in melts bearing smaller RE cations tends to inhibit glass formation. Both XANES and high‐energy X‐ray diffraction indicate increases in nTiO as the liquids supercool and vitrify. Results are discussed in the context of alkali and alkaline‐earth titanate glasses, extending the observed dependence of nTiO on structural basicity (modifier content divided by potential) to trivalent modifiers and the molten state. We suggest that the most stable titanate glasses form close to compositions where, on average, two oxygen anions bond to each titanium, allowing a continuous, disordered Ti‐O network of bridging oxygen (OTi2), or with equal numbers of OTi3 triclusters and OTi1 non‐bridging oxygen in charge‐balance. We report on new glasses formed from praseodymium, europium, and gadolinium titanate melts, the latter being the smallest rare‐earth for which binary titanate glasses have been obtained.