Misfit Stresses Caused by Atomic Size Mismatch: The Origin of Doping-Induced Destabilization of Dicalcium Silicate

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• 作者：Peng Guo ; Bu Wang ; Mathieu Bauchy ; Gaurav Sant
• 刊名：Crystal Growth & Design
• 出版年：2016
• 出版时间：June 1, 2016
• 年：2016
• 卷：16
• 期：6
• 页码：3124-3132
• 全文大小：477K
• 年卷期：0
• ISSN：1528-7505

文摘

Density functional theory (DFT) simulations are carried out to systemically investigate doping in dicalcium silicate (Ca₂SiO₄: C₂S), a major phase in calcium silicate cements. By evaluating the energetics of defect formation mechanisms for species involving Na⁺, K⁺, Mg²⁺, Sr²⁺, Al³⁺, Fe³⁺, B³⁺, and Ge⁴⁺, we find a strong site preference for all cationic substitutions. As a result, distinct defects form at low dopant concentrations (i.e., ≤ 0.52 atom %), in which, expectedly, larger dopants prefer (larger) Ca²⁺ sites, while smaller dopants favor (smaller) Si⁴⁺ sites, with charge balance being ensured by the formation of vacancies. Such site preferences arise due to local atomic distortions, which are induced when doping occurs at unfavorable substitution sites. Interestingly, we note that the formation enthalpy of each substitutional defect is proportional to the size mismatch between the dopant and the native cations. This indicates that the destabilization of the C₂S structure has its origins in an “atomic size misfit” which develops while accommodating defects in the C₂S lattice. The outcomes resulting from this work provide insights that are needed to select dopants to optimize cement performance by compositional design.