Unusual Relaxor Ferroelectric Behavior in Stairlike Aurivillius Phases

Abstract

New ferroelectric layered materials were found in the pseudobinary system Bi5Nb3O15-ABi2Nb2O9 (A= Ba, Sr and Pb). Preliminary observations made by transmission electron microscopy indicate that these compounds exhibit a complex incommensurately modulated structure. A (3 + 1)D structural model is obtained using ab initio phasing by charge flipping based on the analysis of precession electron diffraction tomography data. The (3 + 1)D structure is further validated by a refinement against neutron powder diffraction. These materials possess a layered structure with discontinuous [Bi2O2] slabs and perovskite blocks. While these structural units are characteristics of Aurivillius phases, the existence of periodic crystallographic shear planes offers strong similarities with collapsed or stairlike structures known in high-Tc superconductors and related compounds. Using dielectric spectroscopy, we study the phase transitions of these new layered materials. For A = Ba and Sr, a Vögel-Fulcher-like behavior characteristic of the so-called relaxor ferroelectrics is observed and compared to "canonical" relaxors. For A = Sr, the absence of a Burns temperature separated from the freezing temperature appears as a rather unusual behavior.

3D Electron Diffraction: The Nanocrystallography Revolution

“…Sketch showing some representative structures solved by 3D ED method for different classes of materials. Starting from the upper left and going anticlockwise: the mineral karibibite, 133 a tunnel (Na,Mn)-oxide for electrolytic applications, 124 the aperiodic structure of SrBi 7 NbO 24 , 122 the extra-large-pore silicoaluminophosphate ITQ-51, 25 the cobat tetraphosphonate MOF Co-CAU-36, 66 the pharma compound carbamazepine-III, 29 the amyloid core of the Sup35 prion protein, 47 and a new monoclinic polymorph of lysozyme. 45 …”

Exotic Compositional Ordering in Manganese–Nickel–Arsenic (Mn‐Ni‐As) Intermetallics

“…The PEDT data set was analyzed using the computer programs PETS2.0 12 , SUPERFLIP 13 , and JANA2006. 14 Details about the methodology to solve incommensurately modulated structures using PEDT can be found elsewhere [15][16][17][18] . For each data set, the result is a list of hklm indices with associated intensities and estimated standard deviations based on counting statistics (Table 1).…”

NEXAFS–Spectra and Magnetic Susceptibility of Nickel and Chromium Doped of Bismuth Niobate

“…The Aurivillius phases are a large family of bismuth-containing layered perovskite-like compounds whose composition is described by the general formula (Bi 2 O 2 )(A n-1 B n O 3n+1 ), where Bi 2 O 2 are bismuth oxygen layers and A n-1 B n O 3n+1 are perovskite-like fragments consisting of bounded tops of octahedrons ВO 6 with placement of large cations A in cuboctahedral voids between them [1][2][3][4][5][6][7]. The value of the coefficient n in this formula corresponds to the number of octahedrons BO 6 by the thickness of a perovskite-like fragment and can vary from 1 to 5 and more.…”