Rare‐earth titanate melt structure and glass formation

Abstract The structure of rare‐earth titanate melts and glasses of composition 17RE ₂ O ₃ .83TiO ₂ 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 ( n _TiO ), 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 OTi ₃ triclusters in melts bearing smaller RE cations tends to inhibit glass formation. Both XANES and high‐energy X‐ray diffraction indicate increases in n _TiO as the liquids supercool and vitrify. Results are discussed in the context of alkali and alkaline‐earth titanate glasses, extending the observed dependence of n _TiO 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 (OTi ₂ ), or with equal numbers of OTi ₃ triclusters and OTi ₁ 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.