Temperature-Driven Structural Transitions in Molten Sodium Borates Na2O–B2O3: X-ray Diffraction, Thermodynamic Modeling, and Implications for Topological Constraint Theory

Alderman, Oliver L. G.; Liška, Marek; Macháček, Jan; Benmore, C. J.; Lin, Alex; Tamalonis, Anthony; Weber, Jacques

doi:10.1021/acs.jpcc.5b10277

Cited by 38 publications

(77 citation statements)

References 57 publications

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“…the glass, consistent with bulk thermal expansion, and is a manifestation of the first diffraction peak (Figure ), which shifts to smaller Q values in the liquid. On the other hand, the bonded metal‐oxygen peaks actually shift to shorter distances in the melts (Figure ), a phenomenon observed for other glass‐forming oxide liquids, including barium titanate, and suggestive of smaller coordination numbers in the melt.…”

Section: Resultsmentioning

confidence: 68%

Rare‐earth titanate melt structure and glass formation

Alderman

Benmore

Tamalonis

et al. 2019

Int J of Appl Glass Sci

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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.

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Section: Resultsmentioning

confidence: 68%

Rare‐earth titanate melt structure and glass formation

Alderman

Benmore

Tamalonis

et al. 2019

Int J of Appl Glass Sci

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“…It was calibrated using a polystyrene ball coated with a CeO 2 powder standard to give a Q range of 0.5-22.5 Å −1 . An aerodynamic levitation and laser heating system was employed to eliminate heterogeneous nucleation at the melt-container interface and thus increasing the propensity for supercooling (Alderman et al, 2016). A droplet was obtained by melting a levitated spherical alumina bead above a conical nozzle (Nordine et al, 2000;Hennet et al, 2006) in a high purity Ar or O 2 atmosphere using a 400W CO2 laser (Synrad Firestar).…”

Section: High-energy X-ray Diffractionmentioning

confidence: 99%

The Structure of Amorphous and Deeply Supercooled Liquid Alumina

et al. 2019

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Liquid Al 2 O 3 has been supercooled more than 500 K below its melting point (T m = 2,327 K) using aerodynamic levitation and laser heating techniques. High energy synchrotron x-ray measurements were performed over a temperature range of 1,817 ≤ T (K) ≤ 2,700 and stroboscopic neutron diffraction at 1,984 and 2,587 K. The diffraction patterns have been fitted with Empirical Potential Structure Refinement (EPSR) models and compared to classical Molecular Dynamics (MD) simulation results. Both sets of models show similar trends, indicating the presence of high populations of AlO 4 and AlO 5 polyhedral units predominantly linked by triply shared oxygen atoms. EPSR reveals that the mean Al-O coordination number changes linearly with temperature with n AlO = 4.41-[1.25 × 10 −4 ] (T-T m), with a 2.5 Å cutoff. Both EPSR and MD simulations reveal a direction of the temperature dependence of the aluminate network structure which moves further away from the glass forming ideal (n AlO = 3) during supercooling. Furthermore, we provide new experimental data and models for amorphous alumina grown by sequential infiltration synthesis of a polymer template. The amorphous solid form likely has a larger Al-O coordination number than the liquid, consistent with expectations for the hypothetical glass.

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“…Herein, we identify molten ionic oxides that exist in the liquid phase at temperatures above their melting points as a new class of liquid absorbents operating at medium to high temperatures. Among the many molten ionic oxides available, [37][38][39] we have focused on sodium and mixed alkali-metal borates. These new liquid absorbents show rapid CO 2 uptake kinetics over the temperature range 500 to 700 C with excellent cyclic regenerability.…”

Section: Introductionmentioning

confidence: 99%