The crystal structure of ZrCr2D≈4 at 50 K ≤ T ≤ 200 K

2020 ◽  
Vol 75 (11) ◽  
pp. 969-973
Author(s):  
Holger Kohlmann
Keyword(s):  
Crystal Structure ◽  
Phase Transition ◽  
Neutron Powder Diffraction ◽  
Laves Phase ◽  
Formula Unit ◽  
Powder Diffraction Data ◽  
Hydrogen Atoms ◽  
Monoclinic Modification ◽  
Laves Phases ◽  
Neutron Powder Diffraction Data

AbstractMany Laves phases take up considerable amounts of hydrogen to form metallic Laves phase hydrides. They frequently undergo phase transitions driven by ordering phenomena for the hydrogen atom distribution. The cubic Laves phase ZrCr2 takes up hydrogen to form a hydride with almost four hydrogen atoms per formula unit, which undergoes a phase transition to a monoclinic modification at a critical temperature Tc = 250.2 K. Its crystal structure was refined based on neutron powder diffraction data on the deuteride (ZrCr2D3.8 type [T = 1.6 K, C2/c]) at four temperatures in the range 50 K ≤ T ≤ 200 K. The monoclinic low-temperature modification features a strongly distorted square anti-prism ZrD8 and three CrD4 polyhedra with almost fully occupied deuterium sites in saddle-like, distorted tetrahedral and planar configurations. Zr–D distances are in the range 201.4(7) pm ≤ d(Zr–D) ≤ 208.5(8) pm and Cr–D distances in the range 172.9(7) pm ≤ d(Cr–D) ≤ 182.4(8) pm.

Structure of the novel ternary hydrides Li4 Tt 2D (Tt = Si and Ge)

2007 ◽  
Vol 63 (1) ◽  
pp. 63-68 ◽  
Author(s):  
Hui Wu ◽  
Michael R. Hartman ◽  
Terrence J. Udovic ◽  
John J. Rush ◽  
Wei Zhou ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Powder Diffraction ◽  
Diffraction Data ◽  
Direct Methods ◽  
Neutron Powder Diffraction ◽  
The Novel ◽  
Powder Diffraction Data ◽  
Hydrogen Atoms ◽  
Neutron Powder Diffraction Data ◽  
Orthorhombic Cell

The crystal structures of newly discovered Li4Ge2D and Li4Si2D ternary phases were solved by direct methods using neutron powder diffraction data. Both structures can be described using a Cmmm orthorhombic cell with all hydrogen atoms occupying Li6-octahedral interstices. The overall crystal structure and the geometry of these interstices are compared with those of other related phases, and the stabilization of this novel class of ternary hydrides is discussed.

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.

The crystal structure of perdeuterated methanol monoammoniate (CD3OD·ND3) determined from neutron powder diffraction data at 4.2 and 180 K

2009 ◽  
Vol 42 (6) ◽  
pp. 1054-1061 ◽  
Author(s):  
A. D. Fortes ◽  
I. G. Wood ◽  
K. S. Knight
Keyword(s):  
Crystal Structure ◽  
Hydrogen Bonds ◽  
Powder Diffraction ◽  
Diffraction Data ◽  
Rietveld Method ◽  
Neutron Powder Diffraction ◽  
Relative Volume ◽  
Powder Diffraction Data ◽  
Orthorhombic Space Group ◽  
Neutron Powder Diffraction Data

The crystal structure of perdeuterated methanol monoammoniate, CD3OD·ND3, has been solved from neutron powder diffraction data collected at 4.2 and 180 K. The crystal structure is orthorhombic, space groupPbca(Z= 8), with unit-cell dimensionsa= 11.02320 (7),b= 7.66074 (6),c= 7.59129 (6) Å,V= 641.053 (5) Å3[ρcalc= 1162.782 (9) kg m−3] at 4.2 K, anda= 11.21169 (5),b= 7.74663 (4),c= 7.68077 (5) Å,V= 667.097 (4) Å3[ρcalc= 1117.386 (7) kg m−3] at 180 K. The crystal structure was determined byab initiomethods from the powder data; atomic coordinates and anisotropic displacement parameters were subsequently refined by the Rietveld method toRp< 3% at both temperatures. The crystal comprises a sheet-like structure in thebccrystallographic plane, consisting of strongly hydrogen bonded elements; these sheets are stacked along theaaxis, and adjacent sheets are linked by what may be comparatively weak C—D...O hydrogen bonds. Within the strongly bonded sheet structure, ND3molecules are tetrahedrally coordinated by the hydroxy moieties of the methanol molecule, accepting one hydrogen bond (O—D...N) of length ∼1.75 Å, and donating three hydrogen bonds (N—D...O) of length 2.15–2.25 Å. Two of the methyl deuterons appear to participate in weak interlayer hydrogen bonds (C—D...O) of length 2.7–2.8 Å. The hydrogen bonds are ordered at both 4.2 and 180 K. The relative volume change on warming from 4.2 to 180 K, ΔV/V, is +4.06%, which is comparable to, but more nearly isotropic (as determined from the relative change in axial lengths,e.g.Δa/a) than, that observed in deuterated methanol monohydrate.

Crystal Structure of La4Si2O7N2Analyzed by the Rietveld Method Using the Time-of-Flight Neutron Powder Diffraction Data

2003 ◽  
Vol 15 (5) ◽  
pp. 1099-1104 ◽  
Author(s):  
Junichi Takahashi ◽  
Hisanori Yamane ◽  
Naoto Hirosaki ◽  
Yoshinobu Yamamoto ◽  
Takayuki Suehiro ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Powder Diffraction ◽  
Diffraction Data ◽  
Rietveld Method ◽  
Time Of Flight ◽  
Neutron Powder Diffraction ◽  
Powder Diffraction Data ◽  
Neutron Powder Diffraction Data

The crystal structure of cubic C-type samarium sesquioxide, Sm2O3

2019 ◽  
Vol 74 (5) ◽  
pp. 433-435 ◽  
Author(s):  
Holger Kohlmann
Keyword(s):  
Crystal Structure ◽  
Cross Section ◽  
Weighted Average ◽  
High Accuracy ◽  
Neutron Powder Diffraction ◽  
Powder Diffraction Data ◽  
Interatomic Distances ◽  
Data Space ◽  
Neutron Powder Diffraction Data ◽  
Yield Structure

AbstractCubic C-type samarium sesquioxide, Sm2O3, was prepared by thermal decomposition of samarium carbonate. Its crystal structure was refined based on neutron powder diffraction data [space group Ia3̅, a = 1092.77(6) pm] in order to accurately determine the oxygen atom positions. Isotopically enriched 154Sm2O3 was used for the neutron diffraction work because of the enormous absorption cross section of the natural isotopic mixtures for thermal neutrons. Crystal structure refinements by the Rietveld technique confirm the cubic bixbyite type and yield structure data of high accuracy. Interatomic distances between Sm1 (Wyckoff site 8a) and oxygen are 6 × 235.0(2) pm, and between Sm2 (Wyckoff site 24d) and oxygen 2 × 231.6(2) pm, 2 × 233.7(2) pm, 2 × 240.2(2) pm with a weighted average of d̅(Sm–O) = 235.1(2) pm.

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