Hydrothermal Synthesis and Structure Solution of Na2Ca(CO3)2: “Synthetic Analogue‿of Mineral Nyerereite

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• 作者：Pavel N. Gavryushkin ; Victor G. Thomas ; Nadezhda B. Bolotina ; Vladimir V. Bakakin ; Alexander V. Golovin ; Yurii V. Seryotkin ; Dmitry A. Fursenko ; Konstantin D. Litasov
• 刊名：Crystal Growth & Design
• 出版年：2016
• 出版时间：April 6, 2016
• 年：2016
• 卷：16
• 期：4
• 页码：1893-1902
• 全文大小：693K
• ISSN：1528-7505

文摘

Crystals of Na₂Ca(CO₃)₂, the structural analogues of mineral nyerereite, were synthesized using hydrothermal technique at 1 kbar and 450 °C. The crystals are transformational twins formed at the transition from the high-temperature hexagonal modification to the low-temperature orthorhombic modification. The structure was solved and refined to R = 0.059 in P2₁ca (No. 29) space group with a = 10.0713(5) Å, b = 8.7220(2) Å, and c = 12.2460(4) Å. The only structural analogue of the synthesized crystal is the high-temperature modification of K₂Ca(CO₃)₂, which can be considered as a disordered analogue of Na₂Ca(CO₃)₂. Structural analogues among borates and other classes of compounds have not been found. Based on group–subgroup analysis, we propose the structures of high- and intermediate-temperature modifications of Na₂Ca(CO₃)₂. The relations of the determined structure with other polymorphs of Na₂Ca(CO₃)₂ have also been considered.