Neutron Powder Diffraction on Ce11B2C2and Nd11B2C2: A New Model for the Tetragonal Crystal Structure

1999 ◽  
Vol 68 (7) ◽  
pp. 2287-2291 ◽  
Author(s):  
Takahiro Onimaru ◽  
Hideya Onodera ◽  
Kenji Ohoyama ◽  
Hiroki Yamauchi ◽  
Yasuo Yamaguchi
Keyword(s):  
Crystal Structure ◽  
Powder Diffraction ◽  
Neutron Powder Diffraction ◽  
New Model ◽  
Tetragonal Crystal ◽  
Tetragonal Crystal Structure

Use of Neutron Diffraction for Describing Texture of Isostatically-Pressed Molybdite Powders

2005 ◽  
Vol 105 ◽  
pp. 83-88 ◽  
Author(s):  
H. Sitepu ◽  
Heinz Günter Brokmeier
Keyword(s):  
Crystal Structure ◽  
Neutron Diffraction ◽  
Powder Diffraction ◽  
Quantitative Description ◽  
Neutron Powder Diffraction ◽  
Powder Diffraction Data ◽  
Neutron Powder Diffraction Data ◽  
Pole Figures ◽  
Diffraction Patterns ◽  
Excellent Tool

The modelling and/or describing of texture (i.e. preferred crystallographic orientation (PO)) is of critical importance in powder diffraction analysis - for structural study and phase composition. In the present study, the GSAS Rietveld refinement with generalized spherical harmonic (GSH) was used for describing isostatically-pressed molybdite powders neutron powder diffraction data collected in the ILL D1A instrument. The results showed that for texture in a single ND data of molybdite the reasonable crystal structure parameters may be obtained when applying corrections to intensities using the GSH description. Furthermore, the WIMV method was used to extract the texture description directly from a simultaneous refinement with 1368 whole neutron diffraction patterns taken from the sample held in a variety of orientations in the ILL D1B texture goniometer. The results provided a quantitative description of the texture refined simultaneously with the crystal structure. Finally, the (002) molybdite pole-figures were measured using the GKSS TEX2 texture goniometer. The results showed that neutron diffraction is an excellent tool to investigate the texture in molybdite.

scholarly journals Neutron diffraction investigation of the temperature dependence of crystal structure and thermal motions of red HgI2

2007 ◽  
Vol 63 (6) ◽  
pp. 828-835 ◽  
Author(s):  
Dieter Schwarzenbach ◽  
Henrik Birkedal ◽  
Marc Hostettler ◽  
Peter Fischer
Keyword(s):  
Crystal Structure ◽  
Neutron Diffraction ◽  
Powder Diffraction ◽  
Soft Mode ◽  
Layer Structure ◽  
Neutron Powder Diffraction ◽  
Force Constants ◽  
Quantum Oscillator ◽  
Thermal Displacement ◽  
Tetrahedral Layer

The structure of, and anisotropic thermal motions in, the red semiconductor tetrahedral layer structure of HgI2 have been studied with neutron powder diffraction as a function of temperature from 10 to 293 K. Average thermal displacement parameters U eq of the two atoms are comparable in size at 10 K, but U eq(Hg) increases considerably faster with temperature than U eq(I), the Hg—I bond being highly non-rigid. The anisotropic displacement tensor U (I) is strongly anisotropic with one term about twice as large as the others, while U (Hg) is nearly isotropic. All displacement tensor elements, except U 22(I), increase faster with temperature than harmonic quantum oscillator curves indicating a softening of the isolated-atom potentials at large amplitudes. A lattice dynamical model provides arguments that the anisotropic thermal motions of I are dominated by a soft mode with a wavevector at the [½ ½ 0] boundary of the Brillouin zone consisting essentially of coupled librations of the HgI4 tetrahedra, and by translations of the entire layer. The large vibration amplitudes of Hg suggest weak Hg–I force constants compared with the I–I force constants, allowing Hg to move quite freely inside the tetrahedra. The libration mode induces dynamic deformations of the Hg—I bond with twice its frequency. This provides a mechanism for the anharmonicity and may explain the lightening of the color from red to orange upon cooling at ca 80 K.

Mn-Mg disordering in cummingtonite: a high-temperature neutron powder diffraction study

2000 ◽  
Vol 64 (2) ◽  
pp. 255-266 ◽  
Author(s):  
J. J. Reece ◽  
S. A. T. Redfern ◽  
M. D. Welch ◽  
C. M. B. Henderson
Keyword(s):  
Crystal Structure ◽  
Phase Transition ◽  
New York ◽  
High Temperature ◽  
Powder Diffraction ◽  
Elevated Temperatures ◽  
Neutron Powder Diffraction ◽  
Site Preference ◽  
A Site

AbstractThe crystal structure of a manganoan cummingtonite, composition [M4](Na0.13Ca0.41Mg0.46Mn1.00) [M1,2,3](Mg4.87Mn0.13)(Si8O22)(OH)2, (Z = 2), a = 9.5539(2) Å, b = 18.0293(3) Å, c = 5.2999(1) Å, β = 102.614(2)° from Talcville, New York, has been refined at high temperature using in situ neutron powder diffraction. The P21/m to C2/m phase transition, observed as spontaneous strains +ε1 = −ε2, occurs at ˜107°C. Long-range disordering between Mg2+ and Mn2+ on the M(4) and M(2) sites occurs above 550°C. Mn2+ occupies the M(4) and M(2) sites preferring M(4) with a site-preference energy of 24.6±1.5 kJ mol−1. Disordering induces an increase in XMnM2 and decrease in XMnM4 at elevated temperatures. Upon cooling, the ordered states of cation occupancy are ‘frozen in’ and strains in lattice parameters are maintained, suggesting that re-equilibration during cooling has not taken place.

An investigation of the polytypical structure of Sr0.2Ba0.8CoO3–δ by neutron powder diffraction

2010 ◽  
Vol 225 (5) ◽  
Author(s):  
Cristina de la Calle ◽  
José Antonio Alonso ◽  
Ainara Aguadero ◽  
Maria Teresa Fernández-Díaz ◽  
Florence Porcher
Keyword(s):  
Crystal Structure ◽  
Thermal Treatment ◽  
Powder Diffraction ◽  
Oxygen Pressure ◽  
Room Temperature ◽  
Neutron Powder Diffraction ◽  
Slow Cooling ◽  
High Oxygen Pressure ◽  
Citrate Precursor

AbstractThe preparation and characterization of two polymorphs of the title composition are described. One hexagonal perovskite, labeled as “H”, was synthesized by thermal treatment of reactive citrate precursor at 900 °C in high oxygen pressure (20 MPa) followed by slow cooling (10 °C/min) to room temperature. This 1D-structure displays aThe evolution of the crystal structure of the 3C phase has been explored

A Neutron Powder Diffraction Study of the Ferromagnetic Superconductor RuSr2(Gd1.3Ce0.7)Cu2O10-σ

2000 ◽  
Vol 659 ◽  
Author(s):  
Christopher S. Knee ◽  
Mark T. Weller
Keyword(s):  
Crystal Structure ◽  
Powder Diffraction ◽  
Magnetic Order ◽  
Oxygen Deficiency ◽  
Structural Response ◽  
Rietveld Analysis ◽  
Neutron Powder Diffraction ◽  
Ferromagnetic Transition ◽  
Copper Site ◽  
Fluorite Type

ABSTRACTThe temperature dependence of the crystal structure of the ferromagnetic superconductor RuSr2(160Gd1.3Ce0.7)Cu2O10-σ, which orders magnetically at TC ∼ 180 K and exhibits a Tc ∼ 30 K, has been investigated by time-of-flight neutron powder diffraction. In this system superconductivity is believed to occur in the CuO2 layers while the magnetic order is associated with the Ru moments. The tetragonal structure evolves from that of YBa2Cu3O7-σ by inserting a fluorite-type Gd1.3Ce0.7O2 layer instead of the Y ion and replacing the chain copper site with RuO6 octahedra. Rietveld analysis reveals that the basal oxygens of the RuO6 octahedra are displaced within the xy-plane to accommodate physically reasonable Ru-O in-plane bonds. These displacements are consistent with rotations of the octahedra by ∼ 15° around the c-axis. Data were collected at 40 K, 70 K, 100 K, 130 K, 150 K, 170 K 190 K and 230 K but no large structural response associated with the ferromagnetic transition is observed. A small level of oxygen deficiency within the (Gd/Ce)2O2−x, fluorite layer (x = 0.1) is detected leading to a refined stoichiometry of RuSr2(Gd1.3Ce0.7)Cu2O9.9.

Crystal Structure of Metastable Tetragonal Zirconia by Neutron Powder Diffraction Study

1993 ◽  
Vol 76 (10) ◽  
pp. 2673-2676 ◽  
Author(s):  
Naoki Igawa ◽  
Yoshinobu Ishii ◽  
Takanori Nagasaki ◽  
Yukio Morii ◽  
Satora Funahashi ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Diffraction Study ◽  
Powder Diffraction ◽  
Tetragonal Zirconia ◽  
Neutron Powder Diffraction ◽  
Metastable Tetragonal Zirconia
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