Local Oxygen-Vacancy Ordering and Twinned Octahedral Tilting Pattern in the Bi0.81Pb0.19FeO2.905 Cubic Perovskite

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• 作者：Walid Dachraoui ; Joke Hadermann ; Artem M. Abakumov ; Alexander A. Tsirlin ; Dmitry Batuk ; Konstantin Glazyrin ; Catherine McCammon ; Leonid Dubrovinsky ; Gustaaf Van Tendeloo
• 刊名：Chemistry of Materials
• 出版年：2012
• 出版时间：April 10, 2012
• 年：2012
• 卷：24
• 期：7
• 页码：1378-1385
• 全文大小：486K
• 年卷期：v.24,no.7(April 10, 2012)
• ISSN：1520-5002

文摘

The structure of Bi_0.81Pb_0.19FeO_2.905 was investigated on different length scales using a combination of electron diffraction, high-resolution scanning transmission electron microscopy, synchrotron X-ray powder diffraction, and M枚ssbauer spectroscopy. In the 80鈥?00 K temperature range, the average crystal structure of Bi_0.81Pb_0.19FeO_2.905 is a cubic Pm3̅m perovskite with a = 3.95368(3) 脜 at T = 300 K. The (Pb²⁺, Bi³⁺) cations and O2鈥?/sup> anions are randomly displaced along the 110 cubic directions, indicating the steric activity of the lone pair on the Pb²⁺ and Bi³⁺ cations and a tilting distortion of the perovskite framework. The charge imbalance induced by the heterovalent Bi^3+聽鈫?Pb²⁺ substitution is compensated by the formation of oxygen vacancies preserving the trivalent state of the Fe cations. On a short scale, oxygen vacancies are located in anion-deficient (FeO_1.25) layers that are approximately 6 perovskite unit cells apart and transform every sixth layer of the FeO₆ octahedra into a layer with a 1:1 mixture of corner-sharing FeO₄ tetrahedra and FeO₅ tetragonal pyramids. The anion-deficient layers act as twin planes for the octahedral tilting pattern of adjacent perovskite blocks. They effectively randomize the octahedral tilting and prevent the cooperative distortion of the perovskite framework. The disorder in the anion sublattice impedes cooperative interactions of the local dipoles induced by the off-center displacements of the Pb and Bi cations. Magnetic susceptibility measurements evidence the antiferromagnetic ordering in Bi_0.81Pb_0.19FeO_2.905 at low temperatures.

Keywords:

perovskite; multiferroic; BiFeO₃; Pb; doping; oxygen vacancy; octahedral tilting; ordering; transmission electron microscopy; HRTEM; ED; HAADF-STEM; ABF-STEM