CaFerrite_DofR.dat from The structure of molten calcium ferrite under various redox conditions

D(r) experimental data from figure 2 of Shi et al. for CaO-Fe2O-x as a function of Fe+

CaFerrite_SofQ.dat from The structure of molten calcium ferrite under various redox conditions

S(Q) experimental data from figure 2 of Shi et al. for CaO-Fe2O-x as a function of Fe+

Continuous Structural Transition in Glass-Forming Molten Titanate BaTi₂O₅

The structure of the model titanate glass former BaTi₂O₅ 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>_TiO = 5.4(1) – [3.5(7) × 10^–4]<i>T</i> [K] (1300 ≤ <i>T</i> ≤ 1830 K, <i>T</i>_g = 960 K, <i>T</i>_m = 1660 K). Comparison to the melt-quenched glass implies an increase in ∂<i>n</i>_TiO/∂<i>T</i> at lower <i>T</i>, as <i>T</i>_g 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>_TiO below its value in pure molten TiO₂, which is related to the presence of density maxima in molten BaO-TiO₂. 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^–3. While BaTi₂O₅ glass likely consists of a fully connected Ti–O network, free of nonbridging oxygen (NBO) [OTi₁] and with at least 13(4)% [OTi₃] triclusters, the 1835(40) K equilibrium melt contains at least 10(4)% NBO along with 90(4)% bridging oxygen [OTi₂]. The results highlight the fact that glasses can be considered as structural analogues of melts <i>only</i> 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. The temperature-dependent structure further implies a super-Arrhenian melt viscosity with consequences for glass manufacture, titanate-rich slags produced in iron smelting, TiO₂-bearing magmas, and by analogy silicate melts at high pressures, as found in planetary interiors