Abstract Knowledge of the detailed structure of iron-bearing aluminosilicate glasses is essential to unraveling the effects of iron on the macroscopic properties of natural silicate glasses and melts. However, the local structures around the framework cations (such as Al and Si) and the extent of network polymerization in iron-bearing aluminosilicate glasses are not well understood. This is mainly because the high-resolution solid-state NMR - one of the effective probes of the structures of aluminosilicate glasses - has limited utility in delving into the local configurations of oxide glasses with paramagnetic elements (i.e., iron). Here, we use multi-nuclear (29Si, 27Al, and 17O) high-resolution solid-state NMR to investigate the effect of iron content on the local structure around framework cations and oxygen species in Na(Al1-XFeX)Si3O8 glasses with varying X [=Fe/(Al + Fe)] (Fe3+/ΣFe = ~0.8), NaAlSi3O8 glasses with varying Fe2O3 (NaAlSi3O8 + Fe2O3, Fe3+/ΣFe = ~0.5), and CaAl2Si2O8 glasses with varying Fe2O3 (CaAl2Si2O8 + Fe2O3, Fe3+/ΣFe = ~0.3). The NMR results for Na(Al1-XFeX)Si3O8 glasses reveal preferential interaction between Fe3+ and Si-rich framework and thus an extensive mixing between [4]Si and [4]Fe3+. The presence of a small amount of [5]Al in Na(Al0.5Fe0.5)Si3O8 glass suggests that the extent of disorder around Al increases by Al-Fe3+ substitution. The NMR results for NaAlSi3O8 + Fe2O3 glasses suggest that Fe2+ interacts more strongly with Al-rich framework and reveal the presence of a non-negligible fraction of Na-NBO, confirming Fe2+-induced structural disorder. The absence of [5]Al in NaAlSi3O8 + Fe2O3 glasses indicates that Fe3+ is more likely to form a highly-coordinated framework (i.e., [5]Fe3+) when excess Fe3+ is added to charge-balanced glasses. The NMR spectra for CaAlSi2O8 + Fe2O3 glasses showed an iron-induced increase in the [5]Al fraction and confirmed that the overall degree of disorder increases with increasing Fe2O3 content. The noble NMR results for iron-bearing aluminosilicate glasses revealed the nature of diverse aspect of iron-induced structural disorder, mainly characterized by the intermixing between Si and Fe3+, preferential interaction between Al and Fe2+, and formation of highly coordinated [5]Fe3+. The detailed iron-induced structural evolution is largely dependent on the composition of melts as well as the valence state of iron. The observed increase in the extent of structural disorder in charge-balanced Na- and Ca-aluminosilicate glasses with increasing Fe2+ and Fe3+ can account for the iron-induced decrease in viscosity of the corresponding iron-bearing aluminosilicate melts.

中文翻译：

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含铁钠长石和钙长石熔体的无序程度：含铁 NaAlSi3O8 和 CaAl2Si2O8 玻璃的多核（29Si、27Al 和 17O）固态 NMR 研究的见解

摘要 了解含铁铝硅酸盐玻璃的详细结构对于阐明铁对天然硅酸盐玻璃和熔体宏观性质的影响至关重要。然而，骨架阳离子（如Al和Si）周围的局部结构以及含铁铝硅酸盐玻璃中网络聚合的程度尚不清楚。这主要是因为高分辨率固态 NMR - 铝硅酸盐玻璃结构的有效探针之一 - 在深入研究具有顺磁性元素（即铁）的氧化物玻璃的局部结构方面的效用有限。在这里，我们使用多核（29Si、27Al、和 17O) 高分辨率固态 NMR，以研究铁含量对具有不同 X [=Fe/(Al + Fe)] 的 Na(Al1-XFeX)Si3O8 玻璃中骨架阳离子和氧物种周围局部结构的影响（ Fe3+/ΣFe = ~0.8)，具有不同 Fe2O3 的 NaAlSi3O8 玻璃（NaAlSi3O8 + Fe2O3，Fe3+/ΣFe = ~0.5），以及具有不同 Fe2O3 的 CaAl2Si2O8 玻璃（CaAl2Si2O8 + Fe2O3，Fe3+/ΣFe = ~0.3）。Na(Al1-XFeX)Si3O8 玻璃的 NMR 结果揭示了 Fe3+ 和富硅骨架之间的优先相互作用，因此 [4]Si 和 [4]Fe3+ 之间存在广泛的混合。Na(Al0.5Fe0.5)Si3O8 玻璃中存在少量 [5]Al 表明 Al 周围的无序程度因 Al-Fe3+ 取代而增加。NaAlSi3O8 + Fe2O3 玻璃的 NMR 结果表明 Fe2+ 与富铝骨架的相互作用更强，并揭示了不可忽略的 Na-NBO 部分的存在，证实了 Fe2+ 诱导的结构无序。NaAlSi3O8 + Fe2O3 玻璃中不存在[5]Al 表明当向电荷平衡玻璃中加入过量的Fe3+ 时，Fe3+ 更有可能形成高度配位的骨架（即[5]Fe3+）。CaAlSi2O8 + Fe2O3 玻璃的 NMR 谱表明，[5]Al 分数由铁诱导增加，并证实总体无序程度随着 Fe2O3 含量的增加而增加。含铁铝硅酸盐玻璃的高贵核磁共振结果揭示了铁诱导结构无序的各个方面的性质，主要特征是 Si 和 Fe3+ 之间的混合，Al 和 Fe2+ 之间的优先相互作用，并形成高度配位的 [5]Fe3+。详细的铁诱导结构演变在很大程度上取决于熔体的组成以及铁的价态。在电荷平衡的 Na- 和 Ca-铝硅酸盐玻璃中观察到的结构无序程度随着 Fe2+ 和 Fe3+ 的增加而增加，可以解释相应含铁铝硅酸盐熔体的铁诱导粘度降低。