Structural systematics in the clathrate hydrates under pressure

2003 ◽  
Vol 81 (1-2) ◽  
pp. 539-544 ◽  
Author(s):  
J S Loveday ◽  
R J Nelmes ◽  
D D Klug ◽  
J S Tse ◽  
S Desgreniers
Keyword(s):  
Room Temperature ◽  
Structural Transition ◽  
Clathrate Hydrates ◽  
Type Ii ◽  
Cage Structure ◽  
X Ray ◽  
Common Features ◽  
Hexagonal Form ◽  
Low Pressures ◽  
Normal Compression

We report the results of synchrotron X-ray and neutron diffraction studies of methane, argon, nitrogen, and xenon clathrate hydrates at high pressure and room temperature. The results reveal common features in the structural transition sequences. All phases transform initially to the hexagonal clathrate structure and all except xenon hydrate eventually form an orthorhombic dihydrate. Argon and nitrogen hydrates adopt the type-II clathrate structure at low pressures and have a tetragonal cage structure between the hexagonal and orthorhombic phases. At normal compression rates, the hexagonal form of xenon hydrate decomposes into ice and xenon at ~2.5 GPa. PACS Nos.: 61.50Ks, 61.10-i, 61.12Ex

Surface analytical study of uranium exposed to low pressures of hydrogen at ∼ 80°C

2012 ◽  
Vol 1444 ◽  
Author(s):  
Robert M. Harker ◽  
Afiya H. Chohollo
Keyword(s):  
Room Temperature ◽  
Analytical Study ◽  
Treatment Cycle ◽  
X Ray Diffraction ◽  
Standard Samples ◽  
X Ray ◽  
Surface Precipitation ◽  
Pre Treatment ◽  
Low Pressures ◽  
Scanning Electron

ABSTRACTIdentical samples of uranium coupons were prepared and each exposed to hydrogen for different times (where this time is significantly less than a classically understood ‘induction time’). Samples were prepared from rolled depleted uranium stock: as-received oxide was removed on all surfaces and two faces (~12x12 mm) were polished to a sub-micron standard. Samples were individually taken through a Vacuum Thermal Pre-Treatment cycle from room temperature to 200°C to the reaction temperature (80°C) over 40 hours and subsequently exposed to 10 mbar O2 for 24 hours. After O2 was removed, the samples were exposed to hydrogen for pre-determined times of up to 48 minutes. Examination of the samples by Scanning Electron Microscopy (SEM) has, as expected, identified small features protruding from the surface believed to have been caused by sub-surface precipitation of UH3. In general these features are circular and isolated from each other, have a diameter of less than 3μm and appear as either ‘flat-topped’ or ‘domed’ morphology. In addition, longer time exposure samples show a predominance of ‘area attack’ where coalesced sub-surface precipitation appears to be confined to particular metal grains. X-Ray Diffraction (XRD) data show an increase in the quantity of UH3 with time.

The crystal structure and temperature dependence of the elpasolite Tl2LiYCl6

2021 ◽  
Vol 54 (2) ◽  
Author(s):  
Drew R. Onken ◽  
Didier Perrodin ◽  
Edith D. Bourret ◽  
Sven C. Vogel
Keyword(s):  
Crystal Structure ◽  
Gamma Rays ◽  
Room Temperature ◽  
Structural Transition ◽  
Radiation Detection ◽  
X Ray Diffraction ◽  
Space Group ◽  
X Ray ◽  
Industry Standard ◽  
The Impact

Tl2LiYCl6 (TLYC) is an analog to Cs2LiYCl6, which is currently an industry-standard inorganic scintillator for radiation detection with good gamma–neutron discrimination. The presence of thallium (Z = 81) instead of cesium (Z = 55) in the elpasolite structure increases the density of the compound and its stopping power for gamma rays. This work investigates the impact of the Tl atom on the elpasolite structure. Single-crystal X-ray diffraction at room temperature and powder neutron diffraction with temperature control were used to characterize the crystal structure of TLYC between 296 and 725 K. The presence of Tl leads to a distortion of the cubic elpasolite structure at room temperature: a tetragonal P42 crystal structure (space group 77, a = 10.223, c = 10.338 Å) is identified for TLYC at 296 K. A structural transition to the cubic elpasolite Fm 3 m phase (space group 225) is observed at 464 K. The thermal expansion of the material for each crystal direction is well described by a linear relationship, except for the region between 400 and 464 K where the lattice parameters converge.

scholarly journals Glow discharge effect on temperature and time of treatment for the synthesis of Mo-doped manganite

DYNA ◽  
2019 ◽  
Vol 86 (209) ◽  
pp. 225-229
Author(s):  
Iván Supelano Gracía ◽  
William Arnulfo Aperador Pacheco ◽  
Carlos Parra Vargas ◽  
Armando Sarmiento Santos
Keyword(s):  
Glow Discharge ◽  
Room Temperature ◽  
Structural Transition ◽  
Rietveld Analysis ◽  
X Ray Diffraction ◽  
X Ray ◽  
Air Atmosphere ◽  
Inflection Points ◽  
Xrd Patterns ◽  
Time And Energy

We report the synthesis of CaMn0.9Mo0.1O3 manganite by glow discharge (GD) plasma treatment under Argon-Air atmosphere. The morphological, structural and magnetic properties were evaluated by scanning electron microscopy (SEM), X-ray diffraction (XRD) and magnetization measures. The results from these measures reveal that the properties of GD synthesized manganite are similar to that exhibited by CaMn0.9Mo0.1O3 produced by conventional resistive furnace. The Rietveld analysis of XRD patterns performed at room temperature show that the samples crystallize in orthorhombic structure of Pnma (62) space group. The magnetization curves as a functionof temperature show two inflection points related to paramagnetic-antiferromagnetic and structural transition. The GD treatment produces a compound with similar properties, reducing the time and energy consumption in comparison with conventional synthesis route by using resistive furnace.

Rare Earth Distribution in NaRF4: Effect on Up-Conversion Intensity

2013 ◽  
Vol 28 (S2) ◽  
pp. S41-S50 ◽  
Author(s):  
H.F. Brito ◽  
J. Hölsä ◽  
T. Laamanen ◽  
T. Laihinen ◽  
M. Lastusaari ◽  
...  
Keyword(s):  
Rare Earth ◽  
Luminescence Intensity ◽  
Room Temperature ◽  
Precipitation Method ◽  
X Ray ◽  
Hexagonal Form ◽  
Prepared Material ◽  
Structural Details ◽  
Co Precipitation ◽  
Very High

The NaYF4:Yb3+,Tb3+ (xYb: 0.20, xTb: 0.04) materials were prepared by the co-precipitation method. The as-prepared material was washed with and without water and thereafter annealed at 500 °C. This resulted in materials with moderate (with water) and very high (without water) up-conversion luminescence intensity. The structural details causing the differences in luminescence intensity were investigated at room temperature with X-ray powder diffraction and Rietveld analyses. All materials crystallized in the hexagonal form (P63/m, No. 176, Z: 1.5) with a composition very close to stoichimetric. The local structural details revealed microstrains in the rare earth sublattice that were relaxed for the material with very high up-conversion luminescence intensity thus decreasing energy losses and enhancing up-conversion.

Electron Microscopy of Human Gallstones

1971 ◽  
Vol 29 ◽  
pp. 296-297
Author(s):  
C. Wolpers ◽  
R. Blaschke
Keyword(s):  
Electron Microscopy ◽  
Room Temperature ◽  
Bile Pigment ◽  
X Ray Diffraction ◽  
Triclinic Crystal System ◽  
X Ray ◽  
Follow Up Study ◽  
Infra Red ◽  
Main Components

Scanning microscopy was used to study the surface of human gallstones and the surface of fractures. The specimens were obtained by operation, washed with water, dried at room temperature and shadowcasted with carbon and aluminum. Most of the specimens belong to patients from a series of X-ray follow-up study, examined during the last twenty years. So it was possible to evaluate approximately the age of these gallstones and to get information on the intensity of growing and solving.Cholesterol, a group of bile pigment substances and different salts of calcium, are the main components of human gallstones. By X-ray diffraction technique, infra-red spectroscopy and by chemical analysis it was demonstrated that all three components can be found in any gallstone. In the presence of water cholesterol crystallizes in pane-like plates of the triclinic crystal system.

Opening images of synaptic vesicles and calcium localization by means of microwave fixation method

1990 ◽  
Vol 48 (2) ◽  
pp. 182-183
Author(s):  
Vinci Mizuhira ◽  
Hiroshi Hasegawa
Keyword(s):  
Synaptic Vesicles ◽  
Room Temperature ◽  
Osmium Tetroxide ◽  
Sampling Procedure ◽  
Fixation Method ◽  
Potassium Oxalate ◽  
X Ray ◽  
Cacodylate Buffer ◽  
Ultrathin Sections ◽  
Microwave Fixation

Microwave irradiation (MWI) was applied to 0.3 to 1 cm3 blocks of rat central nervous system at 2.45 GHz/500W for about 20 sec in a fixative, at room temperature. Fixative composed of 2% paraformaldehyde, 0.5% glutaraldehyde in 0.1 M cacodylate buffer at pH 7.4, also contained 2 mM of CaCl2 , 1 mM of MgCl2, and 0.1% of tannic acid for conventional observation; and fuether 30-90 mM of potassium oxalate containing fixative was applied for the detection of calcium ion localization in cells. Tissue blocks were left in the same fixative for 30 to 180 min after MWI at room temperature, then proceeded to the sampling procedure, after postfixed with osmium tetroxide, embedded in Epon. Ultrathin sections were double stained with an useal manner. Oxalate treated sections were devided in two, stained and unstained one. The later oxalate treated unstained sections were analyzed with electron probe X-ray microanalyzer, the EDAX-PU-9800, at 40 KV accelerating voltage for 100 to 200 sec with point or selected area analyzing methods.

Evidence for ordered Fe3Ni

1987 ◽  
Vol 45 ◽  
pp. 216-217
Author(s):  
K.B. Reuter ◽  
D.B. Williams ◽  
J.I. Goldstein
Keyword(s):  
Experimental Data ◽  
Martensitic Transformation ◽  
Electron Diffraction ◽  
Room Temperature ◽  
Direct Evidence ◽  
Transformation Product ◽  
Iron Meteorites ◽  
X Ray ◽  
Ni Content ◽  
Temperature Transformation

In the Fe-Ni system, although ordered FeNi and ordered Ni3Fe are experimentally well established, direct evidence for ordered Fe3Ni is unconvincing. Little experimental data for Fe3Ni exists because diffusion is sluggish at temperatures below 400°C and because alloys containing less than 29 wt% Ni undergo a martensitic transformation at room temperature. Fe-Ni phases in iron meteorites were examined in this study because iron meteorites have cooled at slow rates of about 10°C/106 years, allowing phase transformations below 400°C to occur. One low temperature transformation product, called clear taenite 2 (CT2), was of particular interest because it contains less than 30 wtZ Ni and is not martensitic. Because CT2 is only a few microns in size, the structure and Ni content were determined through electron diffraction and x-ray microanalysis. A Philips EM400T operated at 120 kV, equipped with a Tracor Northern 2000 multichannel analyzer, was used.

Electron Microscope study of commensurate-incommensurate phase transition in BaZnGeO4

1990 ◽  
Vol 48 (4) ◽  
pp. 172-173
Author(s):  
Naoki Yamamoto ◽  
Makoto Kikuchi ◽  
Tooru Atake ◽  
Akihiro Hamano ◽  
Yasutoshi Saito
Keyword(s):  
Phase Transition ◽  
Electron Microscope Study ◽  
Room Temperature ◽  
Hexagonal Lattice ◽  
Ferroelectric Materials ◽  
Temperature Phase ◽  
X Ray Diffraction ◽  
X Ray ◽  
Periodic Arrays ◽  
Modulation Wave Vector

BaZnGeO4 undergoes many phase transitions from I to V phase. The highest temperature phase I has a BaAl2O4 type structure with a hexagonal lattice. Recent X-ray diffraction study showed that the incommensurate (IC) lattice modulation appears along the c axis in the III and IV phases with a period of about 4c, and a commensurate (C) phase with a modulated period of 4c exists between the III and IV phases in the narrow temperature region (—58°C to —47°C on cooling), called the III' phase. The modulations in the IC phases are considered displacive type, but the detailed structures have not been studied. It is also not clear whether the modulation changes into periodic arrays of discommensurations (DC’s) near the III-III' and IV-V phase transition temperature as found in the ferroelectric materials such as Rb2ZnCl4.At room temperature (III phase) satellite reflections were seen around the fundamental reflections in a diffraction pattern (Fig.1) and they aligned along a certain direction deviated from the c* direction, which indicates that the modulation wave vector q tilts from the c* axis. The tilt angle is about 2 degree at room temperature and depends on temperature.

Investigation of the V4+-Centre in 6H- and 4H-SIC by the Method of Spectral-Hole Burning

1998 ◽  
Vol 512 ◽  
Author(s):  
C. Hecht ◽  
R. Kummer ◽  
A. Winnacker
Keyword(s):  
Electronic Properties ◽  
Room Temperature ◽  
Hole Burning ◽  
Band Offset ◽  
Spectral Hole Burning ◽  
Type Ii ◽  
Thermally Stable ◽  
Spectral Hole

ABSTRACTIn the context of spectral-hole burning experiments in 4H- and 6H-SiC doped with vanadium the energy positions of the V4+/5+ level in both polytypes were determined in order to resolve discrepancies in literature. From these numbers the band offset of 6H/4H-SiC is calculated by using the Langer-Heinrich rule, and found to be of staggered type II. Furthermore the experiments show that thermally stable electronic traps exist in both polytypes at room temperature and considerably above, which may result in longtime transient shifts of electronic properties.

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