Unusual Strong Incommensurate Modulation in a Tungsten-Bronze-Type Relaxor PbBiNb5O15

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• 作者：Kun Lin ; Zhengyang Zhou ; Laijun Liu ; Hongqiang Ma ; Jun Chen ; Jinxia Deng ; Junliang Sun ; Li You ; Hidetaka Kasai ; Kenichi Kato ; Masaki Takata ; Xianran Xing
• 刊名：Journal of the American Chemical Society
• 出版年：2015
• 出版时间：October 28, 2015
• 年：2015
• 卷：137
• 期：42
• 页码：13468-13471
• 全文大小：327K
• ISSN：1520-5126

文摘

Pb- or Bi-based perovskite oxides have been widely studied and used because of their large ferroelectric polarization features induced by stereochemically active 6s² lone pair electrons. It is intriguing whether this effect could exist in other related systems. Herein, we designed and synthesized a mixed Pb and Bi A site polar compound, PbBiNb₅O₁₅, with the TTB framework. The as-synthesized material turns out to be a relaxor with weak macroscopic ferroelectricity but adopts strong local polarizations. What鈥檚 more, unusual five orders of incommensurate satellite reflections with strong intensities were observed under the electron diffraction, suggesting that the modulation is highly developed with large amplitudes. The structural modulation was solved with a (3 + 1)D superspace group using high-resolution synchrotron radiation combined with anomalous dispersion X-ray diffraction technique to distinguish Pb from Bi. We show that the strong modulation mainly originates from lone-pair driven Pb²⁺鈥揃i³⁺ ordering in the large pentagonal caves, which can suppress the local polarization in x鈥?i>y plane in long ranges. Moreover, the as-synthesized ceramics display strong relaxor ferroelectric feature with transition temperature near room temperature and moderate dielectric properties, which could be functionalized to be electromechanical device materials.