Mechanistic Interpretation of the Aurivillius to Perovskite Topochemical Microcrystal Conversion Process

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• 作者：Stephen F. Poterala ; Yunfei Chang ; Trevor Clark ; Richard J. Meyer ; Jr ; Gary L. Messing
• 刊名：Chemistry of Materials
• 出版年：2010
• 出版时间：March 23, 2010
• 年：2010
• 卷：22
• 期：6
• 页码：2061-2068
• 全文大小：1147K
• 年卷期：v.22,no.6(March 23, 2010)
• ISSN：1520-5002

文摘

The kinetics of topochemical and morphological conversion of platelet-shaped Na_3.5Bi_2.5Nb₅O₁₈, PbBi₄Ti₄O₁₅, and BaBi₄Ti₄O₁₅ Aurivillius phases to NaNbO₃, PbTiO₃, and BaTiO₃ perovskites were studied. Reaction of the 001 oriented Aurivillius phases with excess Na₂CO₃, Pb₃(CO₃)₂(OH)₂, and BaCO₃, respectively, yielded high-aspect-ratio perovskite microcrystals with 001 orientation. Only the Na_3.5Bi_2.5Nb₅O₁₈ to NaNbO₃ conversion occurred directly, whereas TEM analysis of reacted BaBi₄Ti₄O₁₅ and PbBi₄Ti₄O₁₅ revealed previously unknown Aurivillius-type intermediate phases with Bi₂O₂²⁺ layers 86 and 78 Å apart, respectively. Observations from TEM and field emission SEM show that perovskite crystallites grow from multiple nucleation sites, but become slightly misaligned during growth. This misalignment is caused by a loss of epitaxy with the parent Aurivillius phase and subsequent exfoliation of the particles, likely caused by the expulsion of byproduct Bi₂O₃ liquid on phase boundaries. This conversion process results in substantial microstructure damage, which is healed with an annealing step between 950 and 1050 °C. The pathway for formation of 001 oriented, polycrystalline or single-crystal perovskite platelets is illustrated in a general model for topochemical conversion of Aurivillius phases.