Temperature Dependence Discontinuity in the Stability of Manganese-Doped Ceria Nanocrystals

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• 作者：Longjia Wu ; Pratik P. Dholabhai ; Blas P. UberuagaRicardo H. R. Castro
• 刊名：Crystal Growth & Design
• 出版年：2017
• 出版时间：February 1, 2017
• 年：2017
• 卷：17
• 期：2
• 页码：446-453
• 全文大小：529K
• ISSN：1528-7505

文摘

CeO₂ has strong potential for chemical-looping water splitting. It has been shown that manganese doping decreases interface energies of CeO₂, allowing increased stability of high surface areas in this oxygen carrier oxide. The phenomenon is related to the segregation of Mn³⁺ at interfaces, which causes a measurable decrease in excess energy. In the present work, it is shown that, despite the stability of nanocrystals of manganese-doped CeO₂ with relation to undoped CeO₂, the effect is strongly dependent on the oxidation state of manganese, i.e., on the temperature. At temperatures below 800 °C, Mn is in the 3+ valence state, and coarsening is hindered by the reduced interface energetics, showing smaller crystal sizes with increasing Mn content. At temperatures above 800 °C, Mn is reduced to its 2+ valence state, and coarsening is enhanced with increasing Mn content. Atomistic simulations show the segregation of Mn to grain boundaries is relatively insensitive to the charge state of the dopant. However, point defect modeling finds that the reduced state causes a decrease in cation vacancy concentration and an increase in cation interstitials, reducing drag forces for grain boundary mobility and increasing growth rates.