scholarly journals X-Ray Investigations of the Low-Temperature Phases of the Organic Metals α- and β-(BEDT-TTF)2I3

1986 ◽  
Vol 41 (11) ◽  
pp. 1319-1324 ◽  
Author(s):  
H. Endres ◽  
H. J. Keller ◽  
R. Swietlik ◽  
D. Schweitzer ◽  
K. Angermund ◽  
...  
Keyword(s):  
Thermal Analysis ◽  
Differential Thermal Analysis ◽  
Room Temperature ◽  
Unit Cell Volume ◽  
Unit Cell ◽  
Slight Variation ◽  
X Ray ◽  
Organic Metals ◽  
Β Phase ◽  
Α Phase

The structure of single crystals of the organic metals α- and β-(BEDT-TTF)2I3* was determined at 100 K, well below the phase transitions indicated by resistivity and thermopower measurements as well as by differential thermal analysis. In the α-phase no unusual change of the room temperature unit cell but a slight variation in the triiodide network and especially a more pronounced dimerization in one of the two donor stacks have been found. The β-phase develops a superstructure with a unit cell volume three times as large as that at room temperature and with pronounced distortions of the I3--ions.

Mechanical Alloying Behavior in the Nb-Si, Ta-Si, and Nb-Ta-Si Systems

1988 ◽  
Vol 133 ◽  
Author(s):  
K. S. Kumar ◽  
S. K. Mannan
Keyword(s):  
High Temperature ◽  
Mechanical Alloying ◽  
Mechanical Milling ◽  
Room Temperature ◽  
Crystalline Compound ◽  
X Ray Diffraction ◽  
X Ray ◽  
Β Phase ◽  
Α Phase

ABSTRACTThe mechanical alloying behavior of elemental powders in the Nb-Si, Ta-Si, and Nb-Ta-Si systems was examined via X-ray diffraction. The line compounds NbSi2 and TaSi2 form as crystalline compounds rather than amorphous products, but Nb5Si3 and Ta5Si3, although chemically analogous, respond very differently to mechanical milling. The Ta5Si3 composition goes directly from elemental powders to an amorphous product, whereas Nb5Si3 forms as a crystalline compound. The Nb5Si3 compound consists of both the tetragonal room-temperature α phase (c/a = 1.8) and the tetragonal high-temperature β phase (c/a = 0.5). Substituting increasing amounts of Ta for Nb in Nb5Si3 initially stabilizes the α-Nb5Si3 structure preferentially, and subsequently inhibits the formation of a crystalline compound.

High-Temperature Modifications of Thorium Dicarbide

1964 ◽  
Vol 8 ◽  
pp. 78-85 ◽  
Author(s):  
P. K. Gantzel ◽  
S. Langer ◽  
N. L. Baldwin ◽  
F. L. Kester
Keyword(s):  
Thermal Analysis ◽  
Differential Thermal Analysis ◽  
High Temperature ◽  
Thermal Effects ◽  
Room Temperature ◽  
Thermal Analyses ◽  
Tetragonal Modification ◽  
X Ray ◽  
Space Groups ◽  
Heating And Cooling

AbstractThermal analyses of samples of thorium dicarbide in equilibrium with graphite show arrests which indicate phase transitions at 1427 ± 21°C arid 1481 ± 28°C. These thermal effects have been observed on heating and cooling both in standard thermal analysis and in differential thermal analysis using graphite as a reference material. The microstructure of thorium dicarbide samples shows the characteristic “herringbone” pattern of a material which has undergone a martensitic-type transition.A high-temperature X-ray investigation has revealed that the observed thermal arrests correspond to erystallographic transformations. The monodinic modification found at room temperature is stable to 1427°C, at which temperature a tetragonal modification with a0 = 4.235 ± 0.002Å and c0 = 5.408 ± 0.002Å is formed. At 1481°C, the tetragonal is transformed to cubic with a0 = 5.809 ± 0.002 Å. The best agreement between observed and calculated intensities has been obtained with C-C units of 1.5-Å assumed bond length in space groups P42/mmc and Pa3 for the tetragonal and cubic modifications, respectively.

scholarly journals Polar and non-polar structures of NH4TiOF3

2019 ◽  
Vol 52 (1) ◽  
pp. 23-26
Author(s):  
O. Boytsova ◽  
I. Dovgaliuk ◽  
D. Chernyshov ◽  
A. Eliseev ◽  
P. O'Brien ◽  
...  
Keyword(s):  
Room Temperature ◽  
Phase 1 ◽  
Structural Features ◽  
X Ray Diffraction ◽  
X Ray ◽  
Β Phase ◽  
Α Phase ◽  
Starting Compound ◽  
Different Temperatures ◽  
Fourfold Axis

Ammonium oxofluorotitanate, NH4TiOF3, is probably the best known precursor for the synthesis of anatase mesocrystals. Transformation of NH4TiOF3 into TiO2 through thermal decomposition, accompanied by hydrolysis, preserves some structural features of the precursor. Currently, any discussion of the mechanism of this transformation is difficult, as the exact crystal structure of the starting compound is not available and no intermediate structures are known. This article describes the outcome of single-crystal and powder X-ray diffraction studies, revealing the existence of two polymorphs of the parent NH4TiOF3 at different temperatures. A second-order phase transition from the polar Pca21 α phase (1), stable at room temperature, to the Pma2 β phase (2) above ∼433 K has been demonstrated. The direction of the pseudo-fourfold axis in NH4TiOF3 coincides with the orientation of the fourfold axis of anatase mesocrystals, consistent with a topotactical transformation.

scholarly journals Thermal Annealing and Phase Transformation of Serpentine-Like Garnierite

Minerals ◽  
2021 ◽  
Vol 11 (2) ◽  
pp. 188
Author(s):  
Arun Kumar ◽  
Michele Cassetta ◽  
Marco Giarola ◽  
Marco Zanatta ◽  
Monique Le Guen ◽  
...  
Keyword(s):  
Thermal Analysis ◽  
Raman Spectroscopy ◽  
Phase Transformation ◽  
Differential Thermal Analysis ◽  
Thermal Treatment ◽  
Room Temperature ◽  
X Ray Diffraction ◽  
Thermally Induced ◽  
X Ray ◽  
Micro Raman Spectroscopy

This study is focused on the vibrational and microstructural aspects of the thermally induced transformation of serpentine-like garnierite into quartz, forsterite, and enstatite occurring at about 620 °C. Powder specimens of garnierite were annealed in static air between room temperature and 1000 °C. The kinetic of the transformation was investigated by means of thermogravimetric and differential thermal analysis, and the final product was extensively characterized via micro-Raman spectroscopy and X-ray diffraction. Our study shows that serpentine-like garnierite consists of a mixture of different mineral species. Furthermore, these garnierites and their composition can provide details based on the mineralogy and the crystalline phases resulting from the thermal treatment.

scholarly journals Solidification transformations in liquid phase separated metastable monotectic Cu – 50 at.% Co alloy

2021 ◽  
Author(s):  
Oluwatoyin Enitan Jegede ◽  
Nafisul Haque ◽  
Andrew M. Mullis ◽  
Robert F. Cochrane
Keyword(s):  
Thermal Analysis ◽  
Differential Thermal Analysis ◽  
Liquid Phase ◽  
Cobalt Content ◽  
Drop Tube ◽  
Gravity Condition ◽  
Β Phase ◽  
Arc Melting ◽  
Α Phase ◽  
Micro Gravity

Metastable monotectic Cu – 50 at. % Co alloy produced by arc melting has been processed under micro gravity condition using a drop tube and subjected to differential thermal analysis (DTA). Microstructural evidence from the as solidified sample revealed that rapid cooling of the arc melt process was enough to incite liquid phase separation in the alloy. In the drop tube samples, the melting temperature of the β- phase (Cu – rich) was determined to be 1294.8 K while that of the α- phase (Co – rich) was found to vary with cobalt content.

X-ray powder diffraction data for nicotine 3,5-dihydroxybenzoate dihydrate, C10H15N2⋅C7H5O4⋅2H2O

2021 ◽  
pp. 1-4
Author(s):  
Ji Yang ◽  
Zhi Hua Liu ◽  
Rui Zhi Zhu ◽  
Neng Jun Xiang ◽  
Shi Yun Tang ◽  
...  
Keyword(s):  
Powder Diffraction ◽  
Diffraction Data ◽  
Room Temperature ◽  
Unit Cell Volume ◽  
Unit Cell ◽  
Powder Diffraction Data ◽  
Unit Cell Parameters ◽  
Space Group ◽  
X Ray ◽  
Cell Parameters

Nicotine 3,5-dihydroxybenzoate dihydrate is a nicotine salt and can be used as compositions in tobacco products. X-ray powder diffraction data, unit-cell parameters, and space group for nicotine 3,5-dihydroxybenzoate, C10H15N2⋅C7H5O4⋅2H2O, are reported [a = 8.424(1) Å, b = 13.179(8) Å, c = 8.591(1) Å, α = 90°, β = 102.073(8)°, γ = 90°, unit-cell volume V = 932.765(3) Å3, Z = 2, ρcal = 1.256 g⋅cm−3, and space group P21] at room temperature. All measured lines were indexed and are consistent with the P21 space group.

Structural analysis of lead magnesium niobate using synchrotron powder X-ray diffraction and the Rietveld method

2016 ◽  
Vol 72 (3) ◽  
pp. 404-409 ◽  
Author(s):  
Ashok Bhakar ◽  
Adityanarayan H. Pandey ◽  
M. N. Singh ◽  
Anuj Upadhyay ◽  
A. K. Sinha ◽  
...  
Keyword(s):  
Cell Volume ◽  
Room Temperature ◽  
Unit Cell Volume ◽  
Rietveld Method ◽  
Unit Cell ◽  
Lead Magnesium Niobate ◽  
Cubic Phase ◽  
X Ray Diffraction ◽  
X Ray ◽  
Lead Magnesium

The room-temperature synchrotron powder X-ray diffraction pattern of the single phase perovskite lead magnesium niobate (PMN) has shown significant broadening in theqrange ∼ 5–7 Å−1compared with standard LaB6synchrotron powder X-ray diffraction data, taken under similar conditions. This broadening/asymmetry lies mainly towards the lower 2θ side of the Bragg peaks. Attempts to fit this data with the paraelectric cubic phase (Pm\bar 3m) and the local rhombohedral phase (R3m) corresponding to polar nanoregions (PNRs) are made using the Rietveld method. Rietveld refinements show that neither cubic (Pm\bar 3m) nor rhombohedral (R3m) symmetry can fit this XRD pattern satisfactorily. The two-phase refinement fits the experimental data satisfactorily and suggests that the weight percentage of the PNRs is approximately 12–16% at room temperature. The unit-cell volume of these rhombohedral PNRs is approximately 0.15% larger than that of the unit cell volume of the paraelectric cubic phase.

Structural, kinetic and thermodynamic aspects of the conformational dimorphism of diethyl 3,6-dibromo-2,5-dihydroxyterephthalate

1996 ◽  
Vol 52 (4) ◽  
pp. 697-706 ◽  
Author(s):  
C. Näther ◽  
N. Nagel ◽  
H. Bock ◽  
W. Seitz ◽  
Z. Havlas
Keyword(s):  
Thermal Analysis ◽  
Differential Thermal Analysis ◽  
Room Temperature ◽  
Molecular Conformation ◽  
Local Energy ◽  
X Ray Diffraction ◽  
Ethanolic Solution ◽  
Crystal Forms ◽  
X Ray ◽  
Ethanol Solvate

The crystal structures of the title compound and of its ethanol solvate have been determined by X-ray diffraction. The compound crystallizes in two different crystal forms (I: P21/n, high-temperature stable modification, II: P21/c, room-temperature stable modification), which differ in molecular conformation and hydrogen bonding. Ab initio calculations show that both observed conformations correspond to local energy minima and predict the conformation in polymorph (II) to be energetically more favourable. Packing energy calculations confirm that form (II) should be more stable than form (I). Crystals of both modifications and a solvate, containing 2 equiv, of ethanol, can be obtained by slow crystallization from ethanolic solution. Modification (II) transforms to (I) at 391 K, as shown by optical microscopy, powder diffraction and differential thermal analysis (DTA), whereas (I) melts at 429 K without previous transformation.

scholarly journals Определение термодинамических параметров в областях фазовых переходов в Cu-=SUB=-1.95-=/SUB=-Ni-=SUB=-0.05-=/SUB=-S

2018 ◽  
Vol 52 (1) ◽  
pp. 76
Author(s):  
Ф.Ф. Алиев ◽  
Г.А. Гасанов ◽  
А.Г. Рзаева ◽  
М.Б. Джафаров ◽  
Г.М. Дамиров
Keyword(s):  
Thermal Analysis ◽  
Differential Thermal Analysis ◽  
Analysis Data ◽  
Differential Thermal Analysis Data ◽  
Heat Absorption ◽  
Thermal Analysis Data ◽  
Β Phase ◽  
Α Phase ◽  
Phase Transition Region ◽  
Alpha Beta

AbstractX-ray diffraction and differential thermal analysis data obtained in the Cu_1.95Ni_0.05S phase-transition region are analyzed. It is established that the low-temperature rhombic α phase in Cu_1.95Ni_0.05S transforms to the hexagonal β phase at temperatures of 370–390 K and to the cubic γ phase at temperatures of 740–765 K according to the scheme $$\alpha \to \mathop {\alpha + \beta }\limits_{370 - 390K} \to \mathop {\alpha + \gamma }\limits_{740 - 765K} \to \gamma $$ α → α + β 370 − 390 K → α + γ 740 − 765 K → γ . It is determined (using the temperature dependence of differential thermal analysis) that the transition α → β is accompanied by heat absorption while the transition β → γ is accompanied by heat release. It is found that both transitions are allowed and belong to the reconstructive type. Both transitions are found to occur in a fluctuation volume of ~10^–20 cm^3 at temperature rates of 0.11 and 0.08 K^–1. It is demonstrated that the transition α → γ is accompanied by alternation of the structures passing through the intermediate β phase, which is incommensurate with respect to the α and γ phases.

A tetranuclear copper (II) complex with pyrazole-3,5-dicarboxylate ligands: synthesis, characterization and electrochemical properties

2016 ◽  
Vol 71 (4) ◽  
pp. 305-310 ◽  
Author(s):  
Selçuk Demir ◽  
Hamide Merve Çepni ◽  
Małgorzata Hołyńska ◽  
Muammer Kavanoz
Keyword(s):  
Crystal Structure ◽  
Thermal Analysis ◽  
Differential Thermal Analysis ◽  
Hydrogen Bonds ◽  
Room Temperature ◽  
Magnetic Measurements ◽  
Metal Oxidation ◽  
X Ray Diffraction ◽  
X Ray ◽  
Complex Anions

AbstractA tetranuclear copper (II) complex with pyrazole-3,5-dicarboxylate ligands (pdc3−), [Me2NH2]4[Cu4(pdc)4], was synthesized using solvothermal and metal oxidation routes and characterized by elemental analysis, infrared, thermogravimetry/differential thermal analysis, and room-temperature magnetic measurements. The structure of the complex was determined by single-crystal X-ray diffraction. It comprises dimethylammonium cations and complex anions containing four Cu2+ cations. The crystal structure is stabilized by N–H···O hydrogen bonds. In addition, the electrochemical behavior was studied.

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