27Al NMR study of the structure of lanthanum- and yttrium-based aluminosilicate glasses and melts.
27Al NMR study of the structure of lanthanum- and yttrium-based aluminosilicate glasses and melts.
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DOI：
10.1021/jp072061q
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发表时间：
2007-07
期刊：
影响因子：
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通讯作者：
P. Florian;N. Sadiki;D. Massiot;J. Coutures
中科院分区：
文献类型：
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作者：
P. Florian;N. Sadiki;D. Massiot;J. Coutures
用~（27）Al核磁共振谱研究了SiO_2含量大于60mol%的Ln（2）O（3）-Al（2）O（3）-SiO_2（Ln = Y或La）三元相图中的某些组分。一维和二维高场（17.6 T）高速（30 kHz）魔角旋转实验已经进行了沿着与模拟的光谱，以量化的五配位铝的量存在于这些玻璃作为组合物的函数。非常高的温度实验允许从2200摄氏度到1700摄氏度跟踪选定的样品，从而表征这些液体中的铝配位状态和动力学。本研究再次加强了目前的观点，即“次要”物种，如五配位铝实际上是存在于铝硅酸盐玻璃中的相当数量，和高温液体在和以上的电荷补偿连接。Y3+和La 3+的高场强揭示了玻璃中第一次由四配位和五配位铝环境感知到的不同平均电场梯度。负责的NMR弛豫铝在高温液体中的运动被证明是不相关的宏观剪切粘度的运动负责。在玻璃和原位高温下获得的结果表明，优先本地化的Ln 3+附近的四配位铝物种，可能形成的三簇和/或Ln 3+的配位变化。
We have investigated by (27)Al nuclear magnetic resonance spectroscopy some compositions in the Ln(2)O(3)-Al(2)O(3)-SiO2 (Ln = Y or La) ternary phase diagram containing more than 60 mol % of SiO2. One- and two-dimensional high-field (17.6 T) high-speed (30 kHz) magic angle spinning experiments have been performed along with simulations of the spectra to quantify the amount of penta-coordinated aluminum present in those glasses as a function of composition. Very high-temperature experiments have allowed to follow selected samples from 2200 degrees C down to 1700 degrees C and hence to characterize the aluminum coordination state and dynamics in those liquids. The present study re-enforces the current view that "minor" species such as penta-coordinated aluminum are actually present in a considerable amount in aluminosilicate glasses, and high-temperature liquids at and above the charge compensation join. The high-field strength of Y3+ and La3+ reveal, for the first time in glasses, a different mean electric field gradient perceived by the tetra- and penta-coordinated aluminum environments. The movements responsible for the NMR relaxation of aluminum in the high-temperature liquid are shown to be uncorrelated with the movements responsible for the macroscopic shear viscosity. Results obtained both on glasses and in situ at high-temperature suggest a preferential localization of Ln3+ nearby tetra-coordinated aluminum species, with possible formation of tricluster and/or Ln3+ coordination changes.