Structure, Atomistic Simulations, and Phase Transition of Stoichiometric Yeelimite

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• 作者：Ana Cuesta ; Angeles G. De la Torre ; Enrique R. Losilla ; Vanessa K. Peterson ; Pawel Rejmak ; Andr茅s Ayuela ; Carlos Frontera ; Miguel A. G. Aranda
• 刊名：Chemistry of Materials
• 出版年：2013
• 出版时间：May 14, 2013
• 年：2013
• 卷：25
• 期：9
• 页码：1680-1687
• 全文大小：448K
• 年卷期：v.25,no.9(May 14, 2013)
• ISSN：1520-5002

文摘

Yeelimite, Ca₄[Al₆O₁₂]SO₄, is outstanding as an aluminate sodalite, being the framework of these type of materials flexible and dependent on ion sizes and anion ordering/disordering. On the other hand, yeelimite is also important from an applied perspective as it is the most important phase in calcium sulfoaluminate cements. However, its crystal structure is not well studied. Here, we characterize the room temperature crystal structure of stoichiometric yeelimite through joint Rietveld refinement using neutron and X-ray powder diffraction data coupled with chemical soft-constraints. Our structural study shows that yeelimite has a lower symmetry than that of the previously reported tetragonal system, which we establish to likely be the acentric orthorhombic space group Pcc2, with a 鈭?a 脳 鈭?a 脳 a superstructure based on the cubic sodalite structure. Final unit cell values were a = 13.0356(7) 脜, b = 13.0350(7) 脜, and c = 9.1677(2) 脜. We determine several structures using density functional theory calculations, with the lowest energy structure being Pcc2 in agreement with our experimental result. Yeelimite undergoes a reversible phase transition to a higher-symmetry phase which has been characterized to occur at 470 掳C by thermodiffractometry. The higher-symmetry phase is likely cubic or pseudocubic possessing an incommensurate superstructure, as suggested by our theoretical calculations which show a phase transition from an orthorhombic to a tetragonal structure. Our theoretical study also predicts a pressure-induced phase transition to a cubic structure of space group I43m. Finally, we show that our reported crystal structure of yeelimite enables better mineralogical phase analysis of commercial calcium sulfoaluminate cements, as shown by R_F values for this phase, 6.9% and 4.8% for the previously published orthorhombic structure and for the one reported in this study, respectively.

Keywords:

sodalite; Rietveld refinement; DFT calculations; phase transition; sulfoaluminate cements