Continuous Structural Transition in Glass-Forming Molten Titanate BaTi<sub>2</sub>O<sub>5</sub> [electronic resource].
- Washington, D.C. : United States. Dept. of Energy. Office of Basic Energy Sciences, 2016. and Oak Ridge, Tenn. : Distributed by the Office of Scientific and Technical Information, U.S. Dept. of Energy
- Physical Description:
- pages 26,974-26,985 : digital, PDF file
- Additional Creators:
- Argonne National Laboratory, United States. Department of Energy. Office of Basic Energy Sciences, and United States. Department of Energy. Office of Scientific and Technical Information
- The structure of the model titanate glass former BaTi<sub>2</sub>O<sub>5</sub> has been studied over a wide temperature (<i>T</i>) range in the molten, supercooled, and glassy states under conditions of aerodynamic levitation. Both high-energy X-ray diffraction and Ti K-edge X-ray absorption spectroscopy reveal a continuous structural transition involving reduction of the cation–oxygen (and oxygen–cation) average coordination numbers and bond lengths with increasing <i>T</i>. Ti–O coordination in the moderately supercooled and equilibrium melt follows a linear trend <i>n</i><sub>TiO</sub> = 5.4(1) – [3.5(7) × 10<sup>–4</sup>]T [K] (1300 ≤ <i>T</i> ≤ 1830 K, <i>T</i><sub>g</sub> = 960 K, <i>T</i><sub>m</sub> = 1660 K). Comparison to the melt-quenched glass implies an increase in ∂n<sub>TiO</sub>/∂T at lower <i>T</i>, as <i>T</i><sub>g</sub> is approached from above. Both Ba–O coordination and bond length also decrease at higher <i>T</i>, and the role of Ba addition is to reduce <i>n</i><sub>TiO</sub> below its value in pure molten TiO<sub>2</sub>, which is related to the presence of density maxima in molten BaO-TiO<sub>2</sub>. Density measurements made by imaging of the levitated melt yielded ρ(<i>T</i>) = 4.82(55) – 0.0004(3)<i>T</i> in units of K and g cm<sup>–3</sup>. While BaTi<sub>2</sub>O<sub>5</sub> glass likely consists of a fully connected Ti–O network, free of nonbridging oxygen (NBO) [OTi<sub>1</sub>] and with at least 13(4)% [OTi<sub>3</sub>] triclusters, the 1835(40) K equilibrium melt contains at least 10(4)% NBO along with 90(4)% bridging oxygen [OTi<sub>2</sub>]. The results highlight the fact that glasses can be considered as structural analogues of melts only for those melts deeply supercooled into the glass transition region. The results imply possible fictive <i>T</i> dependence of titanate glass structure, suggesting applications as, e.g., laser written waveguides with large refractive indices and refractive index contrasts. Furthermore, the temperature-dependent structure further implies a super-Arrhenian melt viscosity with consequences for glass manufacture, titanate-rich slags produced in iron smelting, TiO<sub>2</sub>-bearing magmas, and by analogy silicate melts at high pressures, as found in planetary interiors.
- Published through SciTech Connect., 11/01/2016., "129839", Journal of Physical Chemistry. C 120 47 ISSN 1932-7447 AM, and O. L. G. Alderman; C. J. Benmore; A. Tamalonis; S. Sendelbach; S. Heald; R. Weber.
- Funding Information:
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