玻璃形成熔融钛酸盐BaTi 2 O 5中的连续结构转变,The Journal of Physical Chemistry C

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玻璃形成熔融钛酸盐BaTi ₂ O _5中的连续结构转变
The Journal of Physical Chemistry C ( IF 3.3 ) Pub Date : 2016-11-16 00:00:00 , DOI: 10.1021/acs.jpcc.6b08248
O. L. G. Alderman _{1,

2} , C. J. Benmore ₂ , A. Tamalonis ₁ , S. Sendelbach ₁ , S. Heald ₂ , R. Weber _{1,

2}

Affiliation

在空气悬浮条件下，在熔融，过冷和玻璃态的宽温度（T）范围内研究了模型钛酸盐玻璃形成剂BaTi ₂ O ₅的结构。高能X射线衍射和Ti K边缘X射线吸收光谱都显示出连续的结构转变，随着T的增加，阳离子-氧（和氧-阳离子）平均配位数和键长的减少。在适度过冷和平衡熔融的TiO协调遵循线性趋势Ñ_的TiO = 5.4（1） - [3.5（7）×10 ^-4 ] Ť [K]（1300≤ Ť ≤1830 K，Ť_克= 960 K，T _m = 1660 K）。相比于熔融玻璃骤冷意味着∂增加Ñ_的TiO /∂ Ť在较低Ť，如Ť_克从上方接近。在较高的T下，Ba-O的配位和键长也会降低，而且添加Ba的作用是将n _TiO降低到其在纯熔融TiO ₂中的值以下，这与熔融BaO-TiO _2中存在的最大密度有关。通过对悬浮熔体成像的密度测量得出ρ（T）= 4.82（55）– 0.0004（3）T，单位为K和g cm ^–3。尽管BaTi ₂ O ₅玻璃可能由完全连接的Ti-O网络组成，没有无桥氧（NBO）[OTi ₁ ]且至少具有13（4）％[OTi ₃ ]三角胶，但1835（40）K平衡熔体包含至少10（4）％的NBO以及90（4）％的桥接氧[OTi ₂ ]。结果突出了这样一个事实，即仅对于那些过冷至玻璃化转变区域的熔体，才可以将玻璃视为熔体的结构类似物。结果暗示可能会有虚构的T钛酸盐玻璃结构的依赖性，提示其应用，例如，具有大折射率和折射率对比的激光写入波导。与温度有关的结构进一步暗示了超阿里尼耶熔体粘度，这对玻璃制造，铁熔炼中产生的富含钛酸盐的熔渣，含TiO _2的岩浆以及类比于高温的硅酸盐熔体产生了影响，如行星内部所见。

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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 (T) 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 T. Ti–O coordination in the moderately supercooled and equilibrium melt follows a linear trend n_TiO = 5.4(1) – [3.5(7) × 10^–4]T [K] (1300 ≤ T ≤ 1830 K, T_g = 960 K, T_m = 1660 K). Comparison to the melt-quenched glass implies an increase in ∂n_TiO/∂T at lower T, as T_g is approached from above. Both Ba–O coordination and bond length also decrease at higher T, and the role of Ba addition is to reduce n_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(T) = 4.82(55) – 0.0004(3)T 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 only for those melts deeply supercooled into the glass transition region. The results imply possible fictive T 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.

更新日期：2016-11-16

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