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. K E Y W O R D Scharacterization, glass forming melts, glass forming systems, structure, X-ray absorption, X-ray diffraction Oliver L. G. Alderman is recognized as IJAGS Outstanding Young Researcher. |ALDERMAN Et AL. 65The ionic radii 54 are for trivalent cations in sixfold coordination to oxygen, for sake of comparison. "-" indicate lack of any glass formation for the 17RE 2 O 3 .83TiO 2 compositions tested herein. a In argon gas flow only. b Batched as CeO 2 . 2 How to cite this article: Alderman OLG, Benmore CJ, Tamalonis A, Weber R. Rare-earth titanate melt structure and glass formation. Int J Appl Glass Sci.

Inhibiting effect of heterogeneous cations aggregation enhanced by oxygen deficiency on glass formation of BaTi2O5 melts

“…The CN TiO increase from about 4.64 (~2050 K, superheated melt) to about 5.0 (~1520 K, undercooled melt), approximately in accord with variation tendency of the r TiO . However, the CN TiO are quite close under two different atmospheres, which is different from r TiO but is consistent with Alderman's measurement using Ti K‐edge X‐ray absorption spectroscopy 24 . It should be emphasized that the structural feature that shows close CN TiO but discrete r TiO , of Ti‐O pair under two atmosphere seems to go against the prediction from classical Bond‐Valence (BV) theory 64 .…”

“… and are positive constant, and the symbol ~ denotes a scaling relation not a true equality. They supposed that 5 ( 2) corresponds to a better GFA of BT2 melt 24,25 . These pioneering work have a potential assumption that the titanate glasses are 3D continuous disorder network constructed by [TiO m ] polyhedra.…”

“…Classical approaches developed from the structure of oxide glasses, such as Zachariasen's continuous random network model 15 and followed topological constraint theory, 16,17 have been shown useful to correlate atomic structure with glass‐forming properties in various systems, for example, silicates, borates, and multiple network‐forming systems 17–21 . However, challenges exist when applying these Classical approaches to these innovative glass systems (including titanate‐based glasses): (i) Highly‐coordinated structural units ([TiO m ] polyhedra, m ≥ 4) and multi‐types sharing modes (corner, edge, and face) between these structural units existing in the glasses (melts) 22–26 directly conflict with the hypothesis of the Zachariasen's model. (ii) The role of oxides (formers, intermediates, modifiers) for network formation may be not always stereotyped in these systems, as illustrated in lanthanum‐niobate (La 2 O 3 ‐Nb 2 O 5 ) glasses that the typical modifier oxides La 2 O 3 undertakes the construction of continuous network, 4 which extremely complicates the analysis of bound state based on topological constraint theory.…”

Octahedral oxide glass network in ambient pressure neodymium titanate

“…Lanthanum and neodymium titanates were the first to be successfully vitrified, using roller quenching 1 , with compositions near deep eutectics in the binary oxide phase diagrams. Application of containerless melting later led to discovery of a larger family of titanate glasses 2 – 4 . These materials are promising for optical technologies because of their high refractive indices (> 2.1 1 , 5 ), low dispersion 3 , wide transmission range over visible and infrared wavelengths 1 , 3 , and ferroelectric and dielectric properties as glass-ceramics 6 – 8 .…”

“…These materials are promising for optical technologies because of their high refractive indices (> 2.1 1 , 5 ), low dispersion 3 , wide transmission range over visible and infrared wavelengths 1 , 3 , and ferroelectric and dielectric properties as glass-ceramics 6 – 8 . Many titanate glasses also contain large fractions of rare-earth oxides (11–20 mol.% RE 2 O 3 ), making them technologically interesting because of the optical activity of ions such as Nd 3+ , Pr 3+ , and Er 3+ 4 . Optimization of these glasses’ attractive properties can benefit from detailed knowledge of their structure-processing-property relationships, which motivates studies of their atomic structure and glass formation.…”