Pseudocubic Crystal Structure and Phase Transition in Doped Ye鈥檈limite

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• 作者：Ana Cuesta ; 脕ngeles G. De la Torre ; Enrique R. Losilla ; Isabel Santacruz ; Miguel A. G. Aranda
• 刊名：Crystal Growth & Design
• 出版年：2014
• 出版时间：October 1, 2014
• 年：2014
• 卷：14
• 期：10
• 页码：5158-5163
• 全文大小：359K
• ISSN：1528-7505

文摘

Sodalites are tridimensional alumino-silicate materials containing cages where loosely bonded anions are located. Ye鈥檈limite, Ca₄[Al₆O₁₂]SO₄, is outstanding as an aluminate sodalite with a flexible framework accepting several type of dopants with important structural consequences. Moreover, ye鈥檈limite is also important from an applied perspective as it is the most relevant phase in calcium sulfoaluminate cements. The crystal structure of stoichiometric ye鈥檈limite has recently been unraveled, but the structure of dopant-containing ye鈥檈limite, which is present in cements, is not well studied. Here, we report the pseudocubic crystal structure of doped ye鈥檈limite, Ca_3.8Na_0.2Al_5.6Fe_0.2Si_0.2O₁₂SO₄, from high-resolution synchrotron powder diffraction data. The powder pattern is indexed with a cubic cell, and a structural model is reported based on the I4虆3m space group. However, this compound displays diffraction peak narrowing on heating. Furthermore, some high-angle split peaks become a single peak on heating, and a phase transition is measured at 525 掳C. Therefore, it is concluded that the crystal structure at room temperature has a lower symmetry, although it can be described as cubic. The structural study at 800 掳C suggests a truly cubic structure, and we speculate that this phase transition, on heating, is likely related to the dynamical disordering of the sulfate anions. Finally it is concluded that the high temperature cubic state was not quenchable to ambient, even when the tested chemical substituents are introduced into the structure.