An Examination of the Influence of Divalent Cationic Dopants on the Bulk and Surface Properties of Ba(NO3)2 Associated with Crystallization
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- 作者：Robert B. Hammond ; Michael J. Orley ; Kevin J. Roberts ; Robert A. Jackson ; Michael J. Quayle
- 刊名：Crystal Growth & Design
- 出版年：2009
- 出版时间：June 3, 2009
- 年：2009
- 卷：9
- 期：6
- 页码：2588-2594
- 全文大小：293K
- 年卷期：v.9,no.6(June 3, 2009)
- ISSN：1528-7505
文摘
The incorporation of divalent cationic species associated with the crystallization of Ba(NO3)2 related to nuclear waste storage issues is studied via the development and exploitation of a versatile and transferable empirical atom−atom forcefield for both mono- and divalent nitrates. Studies of binary and tertiary systems using Mott−Littleton and bulk supercell defect calculations reveals Cap>2+ p> ions to be the most energetically favored species for incorporation into the Ba(NO3)2 lattice over Srp>2+ p> and Pbp>2+ p> ions. Incorporation modeling also confirms solid−solution behavior with an excellent Vegard’s Law fit. Tertiary systems involving Bap>2+ p>, Cap>2+ p>, and Srp>2+ p> ions are found to become less stable with increasing concentrations, notably of Srp>2+ p>. Morphological predictions using attachment and surface energy methods reveal a well-defined cube-octahedron habit, with negligible differences between Ba(NO3)2 and Sr(NO3)2. Surface relaxation effects are found to be very small, with no apparent impact on the predicted crystal morphology, consistent with a very stable surface structure, reflecting both the close packing nature of the {100} and {111} habit faces and the strong in-plane Coulombic interactions between the cations and the anions. Examination of Srp>2+ p> incorporation onto Ba(NO3)2 crystal habit surfaces is in good agreement with experimental observations of the crystal morphology revealing preferential incorporation onto the {111}surfaces, with respect to the {100} surfaces, where the former case displays a layerlike packing of cations and anions that more easily effects the impurity incorporation process and hence prevents further growth, resulting in a more octahedral morphology.