DETERMINATION OF THE CRYSTAL STRUCTURE OF ERBIUM TITANATE, Er2Ti2O7, BY X-RAY AND NEUTRON DIFFRACTION

1965 ◽  
Vol 43 (10) ◽  
pp. 2812-2826 ◽  
Author(s):  
Osvald Knop ◽  
François Brisse ◽  
Lotte Castelliz
Keyword(s):  
Crystal Structure ◽  
Neutron Diffraction ◽  
Infrared Spectrum ◽  
Least Squares ◽  
Powder Diffraction ◽  
Neutron Powder Diffraction ◽  
X Ray ◽  
X Ray Scattering ◽  
Pyrochlore Type

The crystal structure of erbium titanate, Er2Ti2O7, has been shown by X-ray and neutron powder diffraction to be of the cubic pyrochlore type, with ao = 10.0762 ± 6 Å. Least-squares isotropic refinement based on resolved single reflections gave x(O2) = 0.4200 ± 10 and R = 2.25%. Ionic and neutral X-ray scattering factors gave practically identical results. The six equal Ti—O2 distances in the distorted coordination octahedron of the Ti atom are 1.955 ± 5 Å. The two short (apparent) Er—O distances are 2.1815 ± 5 Å (Er—O1) and 2.471 ± 8 Å (Er—O2). The infrared spectrum of the titanate in the region 1 600 to 250 cm−1 shows features similar to those encountered in the spectra of other simple oxygen compounds of titanium.

Neutron Diffraction from Novel Materials

MRS Bulletin ◽  
1999 ◽  
Vol 24 (12) ◽  
pp. 24-28
Author(s):  
Paolo G. Radaelli ◽  
James D. Jorgensen
Keyword(s):  
Crystal Structure ◽  
Neutron Diffraction ◽  
Rietveld Refinement ◽  
Powder Diffraction ◽  
Diffraction Data ◽  
Neutron Powder Diffraction ◽  
Inorganic Crystal Structure Database ◽  
Powder Diffraction Data ◽  
New Materials ◽  
X Ray

The discovery and development of new materials is the foundation of the science and technology “food chains.” Examples of new materials with novel properties that have stimulated new scientific questions and/or led to new technologies include liquid crystals, advanced batteries, structural ceramics, dielectrics, ferroelectrics, catalysts, high-temperature superconductors, har dmagnets, and magnetoresistive devices. Establishing the crystal structure of a newly discovered Compound is a mandatory first step, but the most important contribution of diffraction techniques is to provide an understanding of the relationships among chemical composition, crystal structure, and physical behavior. In this way, diffraction experiments provide critical Information for testing theories that explain novel behavior and guide the optimization of new materials to meet the demands of emerging technologies.The first samples of newly discovered materials are often polycrystalline. With state-of-the-art neutron powder diffraction data and Rietveld refinement techniques, for structures of modest complexity, the precision for atom positions rivals that obtained by single-crystal diffraction. Rietveld refinement is a method of obtaining accurate values for atom positions and other structural parameters from powder diffraction data by least-squares fitting of a calculated model to the full diffraction pattern. As evidence of thi s success, the Inorganic Crystal Structure Database contains 6044 entries from neutron powder diffraction, 7096 from laboratory x-ray powder diffraction, an d 228 from Synchrotron x-ray powder diffraction. Other reasons for the rapidly growing impact of neutron diffraction include the favorable neutron-scattering cross sections for light elements, the sensitivity to magnetic moments, and the ability to penetrate special sample environments for in situ studies. These strengths are widely accepted and have been exploited for many years. Previous reviews have focused on these topics.

Crystal Structure of the Compound Bi2Zn2/3Nb4/3O7

2002 ◽  
Vol 17 (6) ◽  
pp. 1406-1411 ◽  
Author(s):  
Igor Levin ◽  
Tammy G. Amos ◽  
Juan C. Nino ◽  
Terrell A. Vanderah ◽  
Ian M. Reaney ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Neutron Diffraction ◽  
Powder Diffraction ◽  
Diffraction Data ◽  
Neutron Powder Diffraction ◽  
Neutron Diffraction Data ◽  
Structural Refinement ◽  
Large Component ◽  
X Ray ◽  
Thermal Displacements

The crystal structure of Bi2Zn2/3Nb4/3O7 was determined using a combination of electron, x-ray, and neutron powder diffraction. The compound crystallizes with a monoclinic zirconolite-like structure [C2/c (No.15) space group, a = 13.1037(9) Å, b = 7.6735(3) Å, c = 12.1584(6) Å, β = 101.318(5)°]. According to structural refinement using neutron diffraction data, Nb preferentially occupies six-fold coordinated sites in octahedral sheets parallel to the (001) planes, while Zn is statistically distributed between two half-occupied (5 + 1)-fold coordinated sites near the centers of six-membered rings of [Nb(Zn)O6] octahedra. The Nb/Zn cation layers alternate along the c-axis with Bi-layers, in which Bi cations occupy both eight- and seven-fold coordinated sites. The eight-fold coordinated Bi atoms exhibited strongly anisotropic thermal displacements with an abnormally large component directed approximately along the c-axis (normal to the octahedral layers).

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