Crystal Structures and in-Situ Formation Study of Mayenite Electrides
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- 作者：Luis Palacios ; Á ; ngeles G. De La Torre ; Sebastiá ; n Bruque ; Jose L. Garcí ; a-Muñ ; oz ; Santiago Garcí ; a-Granda ; Denis Sheptyakov ; Miguel A. G. Aranda
- 刊名：Inorganic Chemistry
- 出版年：2007
- 出版时间：May 14, 2007
- 年：2007
- 卷：46
- 期：10
- 页码：4167 - 4176
- 全文大小：403K
- 年卷期：v.46,no.10(May 14, 2007)
- ISSN：1520-510X
文摘
Mayenite inorganic electrides are antizeolite nanoporous materials with variable electron concentration[Ca12Al14O32]2+
ntities/square.gif">5-
O1-2-e2- (0 < ntities/le.gif"> 1), where ntities/square.gif"> stands for empty sites. The oxymayenite crystal structurecontains positively charged cages where loosely bounded oxide anions are located. These oxygens can be removedto yield electron-loaded materials in which the electrons behave like anions (electrides). Here, a new preparationmethod, which allows synthesizing powder mayenite electrides easily, is reported. Accurate structural data for thewhite ( = 0) and green electride ( ~ 0.5) are reported from joint Rietveld refinements of neutron and synchrotronX-ray powder diffraction data and also from single-crystal diffraction. The electride formation at high temperatureunder vacuum has been followed in-situ by neutron powder diffraction. The evolution of mayenite crystal structure,including the changes in the key occupation factor of the intracage oxide anions, is reported. Furthermore, thestability of mayenite framework in very low oxygen partial pressure conditions is also studied. It has been foundthat C12A7 decomposes, at 1373 K in reducing conditions, to give Ca5Al6O14 (C5A3) and Ca3Al2O6 (C3A). Thekinetics of this transformation has also been studied. The fit of the transformed fraction to the classic Avrami-Erofe'ev equation gave an "Avrami exponent", n = 2, which indicates that nucleation is fast and the two-dimensionallinear growth of the new phases is likely to be the limiting factor.
ntities/square.gif">5-O1-2-e2- (0 < ntities/le.gif"> 1), where ntities/square.gif"> stands for empty sites. The oxymayenite crystal structurecontains positively charged cages where loosely bounded oxide anions are located. These oxygens can be removedto yield electron-loaded materials in which the electrons behave like anions (electrides). Here, a new preparationmethod, which allows synthesizing powder mayenite electrides easily, is reported. Accurate structural data for thewhite ( = 0) and green electride ( ~ 0.5) are reported from joint Rietveld refinements of neutron and synchrotronX-ray powder diffraction data and also from single-crystal diffraction. The electride formation at high temperatureunder vacuum has been followed in-situ by neutron powder diffraction. The evolution of mayenite crystal structure,including the changes in the key occupation factor of the intracage oxide anions, is reported. Furthermore, thestability of mayenite framework in very low oxygen partial pressure conditions is also studied. It has been foundthat C12A7 decomposes, at 1373 K in reducing conditions, to give Ca5Al6O14 (C5A3) and Ca3Al2O6 (C3A). Thekinetics of this transformation has also been studied. The fit of the transformed fraction to the classic Avrami-Erofe'ev equation gave an "Avrami exponent", n = 2, which indicates that nucleation is fast and the two-dimensionallinear growth of the new phases is likely to be the limiting factor.