Powder diffraction studies of synthetic calcium and lead apatites

2000 ◽  
Vol 53 (8) ◽  
pp. 679 ◽  
Author(s):  
Jean Y. Kim ◽  
Ronald R. Fenton ◽  
Brett A. Hunter ◽  
Brendan J. Kennedy
Keyword(s):  
Neutron Diffraction ◽  
Rietveld Refinement ◽  
Powder Diffraction ◽  
Diffraction Data ◽  
Lattice Parameters ◽  
Neutron Diffraction Data ◽  
X Ray ◽  
Lead Compounds ◽  
Calcium Compounds ◽  
Cation Sites

The crystal structures of M10(PO4)6X2, where M = Ca or Pb and X = OH¯, F¯, Cl¯ or Br¯, have been determined by Rietveld refinement of powder synchrotron X-ray and neutron diffraction data. All the compounds are hexagonal with space group P 63/m. For the calcium compounds, the lattice parameters are a = 9.4302(5), 9.3475(3), 9.5902(6), 9.6482(6) and c = 6.8911(2), 6.8646(1), 6.7666(2), 6.7788(2) Å, for X = OH¯, F¯, Cl¯, Br¯, respectively. For the lead compounds, the corresponding lattice parameters are a = 9.8612(4), 9.7547(5), 9.9767(4), 10.0618(3) and c = 7.4242(2), 7.2832(2), 7.3255(1), 7.3592(1) Å. In these compounds there are two cation sites, a channel of M(I) atoms and a triangle of M(II) atoms. The anion interacts most strongly with the M(II) atoms with the interaction dictating the position of the anion relative to the M(II) triangle. In Ca10(PO4)6X2, the F¯ ion sits within the triangle planes, while the larger OH¯ and Cl¯ anions are disordered above and below the M(II) triangles. The even larger Br¯ is midway between two triangles at (0, 0, ). Despite the larger size of the isostructural lead compounds, no anions are found in the triangles. The F¯, Cl¯ and Br¯ ions are at (0, 0, ) and the OH¯ ion is disordered at (0, 0, z). This difference in behaviour is possibly related to the lead 6s electrons. In this paper, the experimental results are presented and possible reasons for the observed differences are discussed.

Measurement of Atomic Elastic Constants by Pulsed Neutron Powder Diffraction

1992 ◽  
Vol 36 ◽  
pp. 577-583
Author(s):  
A. C. Lawson ◽  
G. H. Kwei ◽  
J. A. Goldstone ◽  
B. Cort ◽  
R. I. Sheldon ◽  
...  
Keyword(s):  
High Temperature ◽  
Neutron Diffraction ◽  
Rietveld Refinement ◽  
Powder Diffraction ◽  
Elastic Constants ◽  
Diffraction Data ◽  
High Temperature Superconductors ◽  
Neutron Powder Diffraction ◽  
Neutron Diffraction Data ◽  
Pulsed Neutron

AbstractWe have developed a technique for determining the atomic elastic constants from measurements of the Debye-Waller factors. The Debye-Waller factors are obtained by Rietveld refinement of time-of-flight neutron diffraction data and interpreted in terms of an atomic Debye-Waller temperature. The method is applicable to powders and to materials that must be encapsulated for safety or environmental reasons. We will illustrate our technique with applications to actinide metals, to metallic hydrides and to high-temperature superconductors.

X-ray powder diffraction data and Rietveld refinement for a new iodate: (LiFe1/3)(IO3)2

2002 ◽  
Vol 17 (2) ◽  
pp. 132-134
Author(s):  
Y. C. Lan ◽  
X. L. Chen ◽  
Z. Tao ◽  
A. Y. Xie ◽  
P. Z. Jiang ◽  
...  
Keyword(s):  
Rietveld Refinement ◽  
Powder Diffraction ◽  
Diffraction Data ◽  
Hexagonal Structure ◽  
Lattice Parameters ◽  
Powder Diffraction Data ◽  
Cation Site ◽  
Space Group ◽  
X Ray

The structure of a new iodate, (LiFe1/3)(IO3)2, has been determined. The new compound has a hexagonal structure with the lattice parameters a=5.4632(2) Å, c=5.0895(6) Å, Z=1. The density is 4.70 g cm−3. Rietveld refinement confirms that the compound has a space group of P63 (173). Fe and Li atoms randomly distribute on the 2a cation site.

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.

FINAX: a computer program for correcting diffraction angles, refining cell parameters and calculating powder patterns

1983 ◽  
Vol 16 (6) ◽  
pp. 651-653 ◽  
Author(s):  
E. R. Hovestreydt
Keyword(s):  
Neutron Diffraction ◽  
Computer Program ◽  
Powder Diffraction ◽  
Diffraction Data ◽  
Neutron Diffraction Data ◽  
X Ray ◽  
Cell Parameters ◽  
Theoretical Line ◽  
Diffraction Patterns ◽  
Line Positions

A computer program is described, whose purpose is the refinement of cell parameters from X-ray or neutron diffraction data. It is of particular use when working with powder diffraction patterns, as it has the possibility of (a) correcting the measured diffraction angles from reference reflections and of (b) calculating a theoretical powder diffractogram, including intensities. A minimum of crystallographic information has to be given and input is partially in free format. E.s.d.'s in cell parameters, as well as in the volume, are calculated. It handles α 1−α 2 splitting and calculates, apart from the theoretical line positions, also a more realistic position of where to expect a given reflection on the film.

Crystal and X-ray powder diffraction data for orthorhombic BaNd2Mn2O7 phase

1997 ◽  
Vol 12 (2) ◽  
pp. 103-105 ◽  
Author(s):  
Shunkichi Ueno ◽  
Naoki Kamegashira
Keyword(s):  
Rietveld Refinement ◽  
Powder Diffraction ◽  
Diffraction Data ◽  
Lattice Parameters ◽  
Powder Diffraction Data ◽  
Space Group ◽  
X Ray

A Rietveld refinement of X-ray powder diffraction data for orthorhombic BaNd2Mn2O7 is reported. The refined lattice parameters were a=0.5517(5), b=0.5482(3), and c=2.0585(7) nm with space group Fmmm (No. 69).

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).

Solution of heavy atom structures from powder diffraction data using direct methods. A review of structures solved at Aarhus University

2004 ◽  
Vol 19 (4) ◽  
pp. 362-366
Author(s):  
Axel Nørlund Christensen
Keyword(s):  
Neutron Diffraction ◽  
Powder Diffraction ◽  
Diffraction Data ◽  
Inorganic Compounds ◽  
Heavy Atom ◽  
Direct Methods ◽  
Neutron Diffraction Data ◽  
Powder Diffraction Data ◽  
X Ray Diffraction ◽  
X Ray

Heavy atoms dominate the X-ray scattering from many inorganic compounds like oxides and oxalates, and often only partial structures of these compounds can be obtained by X-ray powder diffraction data. Combining information from X-ray and neutron diffraction data is an advantage. Scattering contributions from the atoms are more evenly distributed in neutron diffraction data than in X-ray diffraction data. Neutron diffraction data can then be used to complete a structure partially solved with data from an X-ray diffraction pattern. Examples of heavy atom structures solved in the time period 1983–2004 using direct methods outlined above are presented.

Powder diffraction data for the three-layer Aurivillius ceramics Bi2Sr2−xAxNb2TiO12(A=Ca,Ba,x=0,0.5,1)

2005 ◽  
Vol 20 (1) ◽  
pp. 47-50
Author(s):  
M. S. Haluska ◽  
S. A. Speakman ◽  
S. T. Misture
Keyword(s):  
Neutron Diffraction ◽  
Powder Diffraction ◽  
Diffraction Data ◽  
Rietveld Analysis ◽  
Layered Structures ◽  
Lattice Parameters ◽  
Powder Diffraction Data ◽  
Space Group ◽  
X Ray

Powder diffraction data for five three-layer Aurivillius ceramics of the form Bi2Sr2−xAxNb2TiO12 (A=Ca,Ba,x=0,0.5,1) have been determined from specimens that were characterized using both X-ray and neutron diffraction. Full Rietveld analysis demonstrated that the crystals were all tetragonal (space group I4∕mmm, #139), with highly aniostropic layered structures with lattice parameters on the order of a=3.9 Å and c=33 Å, and densities on the order of 7 g∕cm3

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