Local Crystal Structure of Antiferroelectric Bi2Mn4/3Ni2/3O6 in Commensurate and Incommensurate Phases Described by Pair Distribution Function (PDF) and Rev

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• 作者：Robert J. Szczecinski ; Samantha Y. Chong ; Philip A. Chater ; Helen Hughes ; Matthew G. Tucker ; John B. Claridge ; Matthew J. Rosseinsky
• 刊名：Chemistry of Materials
• 出版年：2014
• 出版时间：April 8, 2014
• 年：2014
• 卷：26
• 期：7
• 页码：2218-2232
• 全文大小：966K
• 年卷期：v.26,no.7(April 8, 2014)
• ISSN：1520-5002

文摘

The functional properties of materials can arise from local structural features that are not well determined or described by crystallographic methods based on long-range average structural models. The room temperature (RT) structure of the Bi perovskite Bi₂Mn_4/3Ni_2/3O₆ has previously been modeled as a locally polar structure where polarization is suppressed by a long-range incommensurate antiferroelectric modulation. In this study we investigate the short-range local structure of Bi₂Mn_4/3Ni_2/3O₆, determined through reverse Monte Carlo (RMC) modeling of neutron total scattering data, and compare the results with the long-range incommensurate structure description. While the incommensurate structure has equivalent B site environments for Mn and Ni, the local structure displays a significantly Jahn鈥揟eller distorted environment for Mn³⁺. The local structure displays the rock-salt-type Mn/Ni ordering of the related Bi₂MnNiO₆ high pressure phase, as opposed to Mn/Ni clustering observed in the long-range average incommensurate model. RMC modeling reveals short-range ferroelectric correlations between Bi³⁺ cations, giving rise to polar regions that are quantified for the first time as existing within a distance of approximately 12 脜. These local correlations persist in the commensurate high temperature (HT) phase, where the long-range average structure is nonpolar. The local structure thus provides information about cation ordering and B site structural flexibility that may stabilize Bi³⁺ on the A site of the perovskite structure and reveals the extent of the local polar regions created by this cation.