title: Unusual Strong Incommensurate Modulation in a Tungsten-Bronze-Type Relaxor PbBiNb5O15.
abstract: Pb- or Bi-based perovskite oxides have been widely studied and used because of their large ferroelectric polarization features induced by stereochemically active 6s(2) 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's 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 Pb(2+)-Bi(3+) ordering in the large pentagonal caves, which can suppress the local polarization in x-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.
authors.forename: Kun
authors.initials: K
authors.lastname: Lin
authors.affiliation: College of Chemistry and Molecular Engineering, Peking University , Beijing 100871, China.
authors.forename: Zhengyang
authors.initials: Z
authors.lastname: Zhou
authors.affiliation: State Key Laboratory Breeding Base of Nonferrous Metals and Specific Materials Processing, Guilin University of Technology , Guilin 541004, China.
authors.forename: Laijun
authors.initials: L
authors.lastname: Liu
authors.forename: Hongqiang
authors.initials: H
authors.lastname: Ma
authors.forename: Jun
authors.initials: J
authors.lastname: Chen
authors.forename: Jinxia
authors.initials: J
authors.lastname: Deng
authors.affiliation: College of Chemistry and Molecular Engineering, Peking University , Beijing 100871, China.
authors.forename: Junliang
authors.initials: J
authors.lastname: Sun
authors.forename: Li
authors.initials: L
authors.lastname: You
authors.affiliation: RIKEN SPring-8 Center , 1-1-1 Kouto, Sayo-cho, Sayo-gun, Hyogo 679-5148, Japan.
authors.forename: Hidetaka
authors.initials: H
authors.lastname: Kasai
authors.affiliation: RIKEN SPring-8 Center , 1-1-1 Kouto, Sayo-cho, Sayo-gun, Hyogo 679-5148, Japan.
authors.forename: Kenichi
authors.initials: K
authors.lastname: Kato
authors.affiliation: RIKEN SPring-8 Center , 1-1-1 Kouto, Sayo-cho, Sayo-gun, Hyogo 679-5148, Japan.|Institute of Multidisciplinary Research for Advanced Materials, Tohoku University , 2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan.
authors.forename: Masaki
authors.initials: M
authors.lastname: Takata
authors.forename: Xianran
authors.initials: X
authors.lastname: Xing