scholarly journals Origin of forbidden reflections in multiferroic Ba2CoGe2O7 by neutron diffraction: symmetry lowering or Renninger effect?

2016 ◽  
Vol 49 (2) ◽  
pp. 556-560 ◽  
Author(s):  
Andrew Sazonov ◽  
Martin Meven ◽  
Georg Roth ◽  
Robert Georgii ◽  
István Kézsmárki ◽  
...  
Keyword(s):  
Neutron Diffraction ◽  
Room Temperature ◽  
Structural Model ◽  
Structural Parameters ◽  
Theoretical Description ◽  
Orthorhombic Symmetry ◽  
X Ray Diffraction ◽  
Multiple Diffraction ◽  
X Ray ◽  
Precise Knowledge

For a symmetry-consistent theoretical description of the multiferroic phase of Ba2CoGe2O7 a precise knowledge of its crystal structure is a prerequisite. In a previous synchrotron X-ray diffraction experiment on multiferroic Ba2CoGe2O7 at room temperature, forbidden reflections were found that favour the tetragonal-to-orthorhombic symmetry lowering of the compound [Hutanu, Sazonov, Murakawa, Tokura, Náfrádi & Chernyshov (2011), Phys. Rev. B, 84, 212101]. Here, the results are reported of room-temperature single-crystal diffraction studies with both hot and cold neutrons to differentiate between genuine symmetry lowering and multiple diffraction (the Renninger effect). A comparison of the experimental multiple diffraction patterns with simulated ones rules out symmetry lowering. Thus, the structural model based on the tetragonal space group P\overline{4}2_{1}m was selected to describe the Ba2CoGe2O7 symmetry at room temperature. The precise structural parameters from neutron diffraction at 300 K are presented and compared with the previous X-ray diffraction results.

scholarly journals X-ray diffraction study of structure of CaO-Al2O3-SiO2 ternary compounds in molten and crystalline states

2020 ◽  
Vol 56 (2) ◽  
pp. 269-277
Author(s):  
V.E. Sokol’skii ◽  
D.V. Pruttskov ◽  
O.M. Yakovenko ◽  
V.P. Kazimirov ◽  
O.S. Roik ◽  
...  
Keyword(s):  
Short Range ◽  
Room Temperature ◽  
Short Range Order ◽  
Structural Parameters ◽  
Range Order ◽  
Reverse Monte Carlo ◽  
X Ray Diffraction ◽  
Xrd Pattern ◽  
X Ray ◽  
Ternary Compounds

Anorthite and gehlenite crystalline structure and short-range order of anorthite melt have been studied by X-ray diffraction in the temperature range from room temperature up to ~ 1923 K. The corresponding anorthite and gehlenite phases were identified as well as amorphous component for anorthite samples having identical shape to XRD pattern of the anorthite melt. The structure factor and the radial distribution function of atoms of the anorthite melt were calculated from the X-ray high-temperature experimental data. The partial structural parameters of the short-range order of the melt were reconstructed using Reverse Monte Carlo simulations.

Structural Characterization of Co70-xNixGa30 Ferromagnetic Shape Memory Alloys

2008 ◽  
Vol 52 ◽  
pp. 103-108 ◽  
Author(s):  
Sidananda Sarma ◽  
A. Srinivasan
Keyword(s):  
Magnetic Susceptibility ◽  
Shape Memory ◽  
Room Temperature ◽  
Structural Parameters ◽  
Ac Magnetic Susceptibility ◽  
X Ray Diffraction ◽  
Ferromagnetic Shape Memory Alloys ◽  
Two Phase ◽  
X Ray ◽  
Ferromagnetic Shape Memory

Polycrystalline ingots of Co70–xNixGa30 (20 ≤ x ≤ 26) ferromagnetic shape memory alloy (FSMA) were prepared by arc melting elemental powders followed by homogenization at 1230 °C for 24 hrs and quenching in liquid nitrogen. Room temperature X-Ray diffraction (XRD) patterns of as-quenched samples exhibited single-phase tetragonal structure for alloy compositions with x = 21 to 26, and a two-phase structure (cubic A2-phase along with weak tetragonal phase) for the alloy with x = 20. Rietveld refinement was performed on the X-ray diffraction patterns to obtain the refined structural parameters. Differential Scanning Calorimeter (DSC) curves recorded from 30 °C to 250 °C revealed martensite-austenite and austenite-martensite transformations in all alloys except the alloy with composition x = 20. Low temperature ac magnetic susceptibility measurements confirmed the existence of martensitic transformations in the alloy with x = 20. The structural transformation temperatures show a linear variation with e/a ratio. All the alloys were ferromagnetic at room temperature. Curie temperature was determined using a high temperature ac magnetic susceptibility measurement set-up.

Lyotropic Phase Behaviour and Structural Parameters of Monosaccharide and Disaccharide Guerbet Branched-Chain β-D-Glycosides

2014 ◽  
Vol 895 ◽  
pp. 111-115 ◽  
Author(s):  
Hairul A.A. Hamid ◽  
Rauzah Hashim ◽  
John M. Seddon ◽  
Nicholas J. Brooks
Keyword(s):  
Self Assembly ◽  
Room Temperature ◽  
Structural Parameters ◽  
Phase Behaviour ◽  
Hydroxyl Groups ◽  
X Ray Diffraction ◽  
X Ray ◽  
Branched Chain ◽  
Optical Polarizing Microscopy ◽  
Water Contents

The phase behaviour and self-assembly structural parameters of a pair of monosaccharide and disaccharide Guerbet branched-chain β-D-glycosides, namely 2-octyldodecyl β-D-glucoside (β-Glc-C12C8) and 2-octyldodecyl β-D-maltoside (β-Mal-C12C8), have been studied by means of optical polarizing microscopy (OPM) and small-angle X-ray diffraction at room temperature (25°C). These compounds are sugar-based glycolipid surfactants having a total chain length of C20, and differ based on the increasing number of hydroxyl groups of the sugar headgroup (glucose and maltose). The repeat spacings obtained by X-ray diffraction as a function of water content have been used to determine the limiting hydration for the two glycosides. At room temperature, β-Glc-C12C8 and β-Mal-C12C8 have limiting hydrations of 22 wt% and 25 wt%, corresponding to 8 10 and 10 12 water molecules per glycoside, respectively. At all water contents between 5 and 29 wt % water, these compounds adopt inverse hexagonal (HII) or fluid lamellar (Lα) phases. The structural parameters of these phases have been determined from the diffraction data, from the X-ray repeat spacings, densities and concentration of the glycosides.

A contribution to the structure of coals from x-ray diffraction studies

1960 ◽  
Vol 252 (1019) ◽  
pp. 557-602 ◽  
Keyword(s):  
Bond Length ◽  
Structural Model ◽  
Structural Parameters ◽  
Amorphous Material ◽  
Average Bond Length ◽  
Size Distributions ◽  
X Ray Diffraction ◽  
X Ray ◽  
Structural Differences ◽  
Average Bond

Detailed X-ray diffraction studies have been carried out on a series of vitrains, anthracites, lignites, durains, fusains and certain coal extracts, of varying rank. The results are interpreted in terms of a basic structural model in which the carbon atoms are arranged in small aromatic layers linked to each other by aliphatic or alicyclic material or by five-membered rings to form large buckled sheets. Data have been obtained on the layer size distributions, the average layer diameters, the average bond length, the proportion of amorphous material and on the nature of the packing. The significance of the various structural parameters deduced from X-ray data is discussed critically. All the results are considered together in an attempt to develop as detailed a structural model as possible. The nature of the coalification process and the structural differences between various macerals are discussed and the results are compared with those deduced from other studies.

Low-temperature X-ray diffraction studies on [Cu(4-Xpz)2]x linear chain polymers (where X = Cl, Br, CH3, H; pz = pyrazolate)

1993 ◽  
Vol 71 (3) ◽  
pp. 331-334 ◽  
Author(s):  
Martin K. Ehlert ◽  
Alan Storr ◽  
Robert C. Thompson ◽  
Frederick W. B. Einstein ◽  
Raymond J. Batchelor
Keyword(s):  
Low Temperature ◽  
Room Temperature ◽  
Copper Ions ◽  
Structural Parameters ◽  
Linear Chain ◽  
Crystallographic Axis ◽  
X Ray Diffraction ◽  
Orthorhombic Space Group ◽  
X Ray ◽  
Cell Parameters

Room temperature and low-temperature (110–140 K) powder diffractograms have been obtained for the polymeric compounds [Cu(4-Xpz)2]x (where X = H, CH3, Cl, and Br), and values of the unit cell parameters (orthorhombic, space group Ibam) a, b, and c have been obtained at both high and low temperatures. A single crystal X-ray diffraction study of the X = H compound at 116 K was completed and the results compared with a published study done at room temperature. The structures of these complexes involve extended chains of pyrazolate-bridged copper ions extending along the c crystallographic axis. The X-ray studies indicate little change in the c parameter with decreasing temperature and small but significant changes in the a or b parameters reflecting changes in interchain packing. This study permits some evaluation of how structural parameters are affected by these variations in interchain packing and how these variations may be affecting the magnitude of magnetic exchange in the compounds.

Polymorphism of naphthazarin and its relation to solid-state proton transfer. Neutron and X-ray diffraction studies on naphthazarin C

1985 ◽  
Vol 399 (1817) ◽  
pp. 295-319 ◽  
Keyword(s):  
Crystal Structure ◽  
Hydrogen Bonding ◽  
Solid State ◽  
Neutron Diffraction ◽  
Room Temperature ◽  
Model Comparison ◽  
Molecular Model ◽  
Molecular Formula ◽  
X Ray Diffraction ◽  
X Ray

The crystal structure of naphthazarin C has been determined by neutron diffraction at 60 and 300 K (λ ═ 0.895 Å; 1 Å ═ 10 -10 m ═ 10 -1 nm) and X-ray diffraction at 300 K. The space group is Pc at 60 K, but P 2 1 /c at 300 K. There are small but significant differences in cell dimensions at the two temperatures: a ═ 7.664 (7.915), b ═ 7.304 (7.262), c ═ 15.16 (15.284) Å; β ═ 114.60 (114.20)°; Z ═ 4; U ═ 771.6 (801.3) Å 3 (values at 300 K in parentheses). Neutron diffraction shows that the Pc and P 2 1 /c structures are related by an order-disorder transition at 110±1 K. Structure analysis (1771 reflections; R F ═ 0.035; R W ═ 0.036) showed that the hydroxyl hydrogens are largely ordered at 60 K, the appropriate molecular formula being 5, 8-dihydroxy-1, 4-naphthadione. Neutron diffraction measurements at 300 K (1769 reflections; R F ═ 0.052) indicated a disordered molecular model with one-half of an hydrogen atom attached to each oxygen. X -ray diffraction measurements on naphthazarin C at 300 K (two independent sets of intensity measurements, one with CuKα and the other with MoKα) support this disordered model. The molecular dimensions for naphthazarin A and B also fit this model. Comparison of the crystal structure of naphthazarin C with those of the A and B polymorphs shows that only the former has intermolecular O─H • • • O hydrogen bonding. The diffraction results combined with the available solid-state n. m. r. data show that there is at room temperature a rapid intramolecular exchange of hydroxylic protons between each pair of oxygen atoms in all three naphthazarin polymorphs. Many 1, 3-diketones exist in an enol form in the solid. These enol forms have been reported to be disordered for about twenty molecules at room temperature (this total includes one molecule studied at 108 K, and four amino-imino systems) and ordered systems have been reported for about fifteen molecules. Intermolecular hydrogen bonding occurs only in a few of these crystals.

scholarly journals Detailed single crystal studies on silicates using neutron diffraction

2014 ◽  
Vol 70 (a1) ◽  
pp. C1110-C1110
Author(s):  
Martin Meven ◽  
G. Gatta
Keyword(s):  
Neutron Diffraction ◽  
Single Crystal ◽  
Room Temperature ◽  
Structural Features ◽  
X Rays ◽  
X Ray Diffraction ◽  
X Ray ◽  
Order And Disorder ◽  
Structural Details ◽  
Displacement Regime

Up to now minerals of the silicate family are an interesting and versatile topic of research. Different members of the epidote, lithium tourmaline and beryl groups with very different structural features were studied on the single crystal diffractometer HEIDI at the hot source of the Heinz Maier-Leibnitz Zentrum in Garching (MLZ) in the recent past. The combination of neutron and X-ray diffraction in combination with other methods revealed for each of the studied minerals valuable information about their structural details. Epidote, an important mineral for metamorphic or magmatic petrology was studied with neutrons at room temperature and at 1070 K. The results confirm the high structural stability with no dehydration and only slight thermal expansion [1]. A combined study with x-ray and neutron diffraction on the complex boro-cyclo-silicate elbaite give insight to the displacement regime and H and O order and disorder respectively [2]. Combined single crystal diffraction with x-rays at room temperature and with neutrons at 2.3 K on pezzottaite, an obverse/reverse twin of the beryl family reveals a complex displacement regime with possible partial H2O replacement [3].

Room-temperature ferroelasticity and unusual sequence of phase transitions in the crystal of (N2H5)3[CdCl5]

2021 ◽  
Vol 77 (4) ◽  
Author(s):  
Monika K. Krawczyk ◽  
Zbigniew Czapla ◽  
Adam Ingram ◽  
Andrzej Kozdraś ◽  
Tadeusz Lis ◽  
...  
Keyword(s):  
Phase Transitions ◽  
Room Temperature ◽  
Structural Changes ◽  
Structural Phase ◽  
Orthorhombic Phase ◽  
Orthorhombic Symmetry ◽  
Structural Phase Transitions ◽  
X Ray Diffraction ◽  
X Ray ◽  
Cl Atoms

On the basis of thermal analysis (DSC, DTA, DTG), single crystal X-ray diffraction experiments, dielectric studies and optical observation, it is found that the (N2H5)3[CdCl5] crystal exhibits several structural phase transitions. At room temperature, the studied crystal exhibits ferroelastic properties and undergoes phase transition from the monoclinic to the orthorhombic phase on heating above 327 K. Upon subsequent cooling, two structural phase transitions at about 323 and 319 K are observed, where the crystal adopts orthorhombic symmetry. The presented phase transitions are unique due to the fact the first heating run results in different structural changes compared to those observed during cooling and subsequent heating/cooling runs. In the studied crystal, N2H5 + ions and 1D chains built up from {CdCl5}3− units bridged by Cl atoms occur. The phase transitions observed can be associated with reorientation of cations and partial disorder of cations as well as Cl atoms.

scholarly journals Room-temperature ultrahigh-resolution time-of-flight neutron and X-ray diffraction studies of H/D-exchanged crambin

2012 ◽  
Vol 68 (2) ◽  
pp. 119-123 ◽  
Author(s):  
Julian C.-H. Chen ◽  
Zoë Fisher ◽  
Andrey Y. Kovalevsky ◽  
Marat Mustyakimov ◽  
B. Leif Hanson ◽  
...  
Keyword(s):  
Neutron Diffraction ◽  
Room Temperature ◽  
Protein Structures ◽  
Atomic Displacement ◽  
Protein Crystal ◽  
X Ray Diffraction ◽  
Resolution Time ◽  
X Ray ◽  
Two Temperatures ◽  
Atomic Displacement Parameters

The room-temperature (RT) X-ray structure of H/D-exchanged crambin is reported at 0.85 Å resolution. As one of the very few proteins refined with anisotropic atomic displacement parameters at two temperatures, the dynamics of atoms in the RT and 100 K structures are compared. Neutron diffraction data from an H/D-exchanged crambin crystal collected at the Protein Crystallography Station (PCS) showed diffraction beyond 1.1 Å resolution. This is the highest resolution neutron diffraction reported to date for a protein crystal and will reveal important details of the anisotropic motions of H and D atoms in protein structures.

Neutron and X-ray single-crystal diffraction from protein microcrystalsviamagnetically oriented microcrystal arrays in gels

2016 ◽  
Vol 72 (7) ◽  
pp. 823-829 ◽  
Author(s):  
Shu Tsukui ◽  
Fumiko Kimura ◽  
Katsuhiro Kusaka ◽  
Seiki Baba ◽  
Nobuhiro Mizuno ◽  
...  
Keyword(s):  
Neutron Diffraction ◽  
Single Crystal ◽  
Structure Determination ◽  
Room Temperature ◽  
X Ray Diffraction ◽  
Single Crystal Diffraction ◽  
X Ray ◽  
Diffraction Structure ◽  
First Time ◽  
Magnetically Aligned

Protein microcrystals magnetically aligned in D2O hydrogels were subjected to neutron diffraction measurements, and reflections were observed for the first time to a resolution of 3.4 Å from lysozyme microcrystals (∼10 × 10 × 50 µm). This result demonstrated the possibility that magnetically oriented microcrystals consolidated in D2O gels may provide a promising means to obtain single-crystal neutron diffraction from proteins that do not crystallize at the sizes required for neutron diffraction structure determination. In addition, lysozyme microcrystals aligned in H2O hydrogels allowed structure determination at a resolution of 1.76 Å at room temperature by X-ray diffraction. The use of gels has advantages since the microcrystals are measured under hydrated conditions.

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