Lodesani Federica, Menziani Maria Cristina, Hijiya Hiroyuki, Takato Yoichi, Urata Shingo, Pedone Alfonso
Department of Chemical and Geological Sciences, University of Modena and Reggio Emilia, via G. Campi 103, 41125, Modena, Italia.
Materials Integration Laboratories, AGC Inc., Yokohama, Kanagawa, 221-8755, Japan.
Sci Rep. 2020 Feb 19;10(1):2906. doi: 10.1038/s41598-020-59875-7.
The comprehension of the nonlinear effects provided by mixed alkali effect (MAE) in oxide glasses is useful to optimize glass compositions to achieve specific properties that depend on the mobility of ions, such as the chemical durability, glass transition temperature, viscosity and ionic conductivity. Although molecular dynamics (MD) simulations have already been applied to investigate the MAE on silicates, less effort has been devoted to study such phenomenon in mixed alkali aluminosilicate glasses where alkali cations can act both as modifiers, forming non-bridging oxygens and percolation channels, and as charge compensator of the AlO units present in the network. Moreover, the ionic conductivity has not been computed yet; thus, the accuracy of the atomistic simulations in reproducing the MAE on the property is still open to question. In this work, we have validated five major interatomic potentials for the classical MD simulations by modelling the structure, density, glass transition temperature and ionic conductivity for three aluminosilicate glasses, (25 - x)NaO - x(KO) - 10(AlO) - 65(SiO) (x = 0, 12.5, 25). It was observed that only the core-shell (CS) polarizable force field well reproduces the experimentally measured MAE on T and the ionic conductivity as well as the higher conductivity of single sodium aluminosilicate glass at low temperature and the higher conductivity of single potassium aluminosilicate glass at high temperature. The MAE is related to the suppression of jump events of the alkaline ions between dissimilar sites in the percolation channels consisting of both sodium and potassium ions as in the case of alkaline silicates. The superior reproducibility of the CS potential is originated from the larger and the flexible ring structures due to the smaller Si-O-Si inter-tetrahedra angle, creating appropriate percolation channels for ion conductivity. We also report detailed assessments for using the potential models including the CS potential for investigating MAE on aluminosilicates.
理解氧化物玻璃中混合碱效应（MAE）所产生的非线性效应，有助于优化玻璃成分，以实现特定性能，这些性能取决于离子迁移率，如化学耐久性、玻璃化转变温度、粘度和离子电导率。尽管分子动力学（MD）模拟已被用于研究硅酸盐中的MAE，但在混合碱铝硅酸盐玻璃中研究这种现象的工作较少，在这种玻璃中，碱金属阳离子既可以作为改性剂，形成非桥氧和渗透通道，也可以作为网络中存在的AlO单元的电荷补偿剂。此外，尚未计算离子电导率；因此，原子模拟在再现该性能上的MAE的准确性仍有待质疑。在这项工作中，我们通过对三种铝硅酸盐玻璃(25 - x)NaO - x(KO) - 10(AlO) - 65(SiO)（x = 0、12.5、25）的结构、密度、玻璃化转变温度和离子电导率进行建模，验证了用于经典MD模拟的五种主要原子间势。结果表明，只有核壳（CS）极化力场能很好地再现实验测量的MAE对玻璃化转变温度和离子电导率的影响，以及单钠铝硅酸盐玻璃在低温下的较高电导率和单钾铝硅酸盐玻璃在高温下的较高电导率。MAE与碱性离子在由钠离子和钾离子组成的渗透通道中不同位点之间跳跃事件的抑制有关，就像碱性硅酸盐的情况一样。CS势的卓越再现性源于较小的Si - O - Si四面体间角所导致的更大且灵活的环结构，为离子传导创造了合适的渗透通道。我们还报告了使用包括CS势在内的势模型研究铝硅酸盐中MAE的详细评估。
