Investigation of the structure and phase transitions of the polymeric inorganic–organic hybrids: [M(Im)4V2O6]∞; M = Mn, Co, Ni, Im = imidazole

2010 ◽  
Vol 67 (1) ◽  
pp. 41-52 ◽  
Author(s):  
Kittipong Chainok ◽  
Kenneth J. Haller ◽  
A. David Rae ◽  
Anthony C. Willis ◽  
Ian D. Williams
Keyword(s):  
Phase Transition ◽  
Low Temperatures ◽  
Stacking Faults ◽  
Local Geometry ◽  
X Ray Diffraction ◽  
Space Group ◽  
X Ray ◽  
Disordered Phase ◽  
Large Hysteresis ◽  
Close Proximity

The polymeric isomorphous hybrid inorganic–organic vanadium oxide compounds [M(Im)4V2O6]∞, M = Mn, Co, Ni, Im = imidazole, were investigated at various temperatures between 100 and 295 K by single-crystal X-ray diffraction. The crystals all contain two-dimensional polymeric sheets packed perpendicular to c* and are 1:1 disordered in the space group P42/n (Z = 8) at 295 K. The disordered phase is reversibly transformed to an I41/a ordered phase (Z = 32) below 281 K for the Mn compound and below 175 K for the Co compound. Within a localized region of the I41/a phase eight imidazoles are in close proximity and seven of these are hydrogen bonded to framework O atoms. The hydrogen-bond connectivity of six of these ligands is unchanged by the phase transition that allows an inversion of the local geometry using an inversion operator that is a symmetry element of P42/n, but not I41/a. The Mn structure has a well defined phase transition but the Co structure shows a large hysteresis and it was necessary to include stacking faults in the modelling of the Co structure at low temperatures. The Ni structure was shown to be partially twinned, but ordered in the space group P2/n (Z = 8) at 100 K, with two different localized regions each containing four pairs of inversion-related imidazoles, hydrogen bonding to framework O atoms involving eight imidazoles in one region and six imidazoles in the other. Models for the phase transition mechanisms are considered.

Bildung von Arsensäure aus [As2Cl8]2Ionen und Ozon. Die Kristallstruktur von PPh4Cl · H3AsO4 / Formation of Arsenic Acid from [As2Cl8]2- Ions and Ozone. Crystal Structure of PPh4Cl · H3AsO4

1992 ◽  
Vol 47 (12) ◽  
pp. 1677-1680 ◽  
Author(s):  
Karin Ruhlandt-Senge ◽  
Alfred-Dirk Bacher ◽  
Ulrich Müller
Keyword(s):  
Crystal Structure ◽  
Low Temperatures ◽  
X Ray Diffraction ◽  
Arsenic Acid ◽  
Subsequent Reaction ◽  
Triclinic Space Group ◽  
Space Group ◽  
X Ray

Reaction of ozone with (PPh4)2[As2Cl8] in CH2C12 at low temperatures yields a red compound, possibly an ozonide. Upon evaporation of the solvent at –78 °C the ozone is released again. At -40 °C or above a subsequent reaction yields PPh4[AsCl6], PPh4Cl · H3AsO4, and other products. The crystal structure of PPh4Cl · H3AsO3 was determined by X-ray diffraction (4253 observed reflexions, R = 0.031). It is triclinic, space group P1̅, and consists of H3AsO4 molecules joined to dimer units via H bridges and associated via O–H · · · Cl- bridges to strands. The packing of the PPh4+ ions is discussed. Products of the reaction of (PPh4)2[Sb2Cl8] with ozone in CH2C12 are PPh4[SbCl6] and (PPh4)2[SbOCl4]2 · 2 CH2Cl2.

TEM Study of the Morphology Of GaN/SiC (0001) Grown at Various Temperatures by MBE

1999 ◽  
Vol 595 ◽  
Author(s):  
W.L. Sarney ◽  
L. Salamanca-Riba ◽  
V. Ramachandran ◽  
R.M Feenstra ◽  
D.W. Greve
Keyword(s):  
Low Temperatures ◽  
Stacking Faults ◽  
Full Width ◽  
X Ray Diffraction ◽  
High Quality ◽  
Double Crystal ◽  
Tem Analysis ◽  
Rocking Curve ◽  
X Ray ◽  
Substrate Temperatures

AbstractGaN films grown on SiC (0001) by MBE at various substrate temperatures (600° - 750° C) were characterized by RHEED, STM, x-ray diffraction, AFM and TEM. This work focuses on the TEM analysis of the films' features, such as stacking faults and dislocations, which are related to the substrate temperature. There are several basal plane stacking faults in the form of cubic inclusions for samples grown at low temperatures compared to those grown at high temperatures. The dislocation density is greatest for the film grown at 600°C, and it steadily decreases with increasing growth temperatures. Despite the presence of various defects, x-ray analysis shows that the GaN films are of high quality. The double crystal rocking curve full width at half maximum (FWHM) for the GaN (0002) peak is less than 2 arc-minutes for all of the films we measured and it decreases with increasing growth temperature.

scholarly journals Structure determination and phase transition behaviour of dimethyl sulfate

2006 ◽  
Vol 62 (2) ◽  
pp. 280-286 ◽  
Author(s):  
Richard M. Ibberson ◽  
Mark T. F. Telling ◽  
Simon Parsons
Keyword(s):  
Phase Transition ◽  
Dimethyl Sulfate ◽  
Monoclinic Structure ◽  
Orthorhombic Structure ◽  
X Ray Diffraction ◽  
Coordination Environment ◽  
Space Group ◽  
X Ray ◽  
First Order ◽  
Transition Behaviour

The crystal structures of phase I and phase II of dimethyl sulfate, (CH3O)2SO2, have been determined using complementary high-resolution neutron powder and single-crystal X-ray diffraction techniques. Below its melting point of 241 K dimethyl sulfate crystallizes in an orthorhombic structure (I) in the space group Fdd2. On cooling below ∼175 K the crystal transforms to a monoclinic structure (II) in the space group I2/a. The molecule is located on a twofold axis (Z′ = 1/2) in both structures. The phase transition is of first order with strong hysteresis. The phase transition results in changes to both the intra- and the intermolecular coordination environment.

scholarly journals Inorganic Anion Regulates the Phase Transition in Two Organic Cation Salts Containing [(4-Nitroanilinium)(18-crown-6)]+ Supramolecules

2017 ◽  
Author(s):  
Yuan Chen ◽  
Yang Liu ◽  
Binzu Gao ◽  
Chuli Zhu ◽  
Zunqi Liu
Keyword(s):  
Phase Transition ◽  
Phase Transitions ◽  
Variable Temperature ◽  
Structural Phase ◽  
High Temperature Phase ◽  
Temperature Phase ◽  
X Ray Diffraction ◽  
Scanning Calorimetry ◽  
Space Group ◽  
X Ray

Two novel inorganic–organic hybrid supramolecular assemblies, namely, (4-HNA)(18-crown-6)(HSO4) (1) and (4-HNA)2(18-crown-6)2(PF6)2(CH3OH) (2) (4-HNA = 4-nitroanilinium), were synthesized and characterized by infrared spectroscopy, single X-ray diffraction, differential scanning calorimetry (DSC), and temperature-dependent dielectric measurements. The two compounds underwent reversible phase transitions at about 255 K and 265 K, respectively. These phase transitions were revealed and confirmed by the thermal anomalies in DSC measurements and abrupt dielectric anomalies during heating. The phase transition may have originated from the [(4-HNA)(18-crown-6)]+ supramolecular cation. The inorganic anions tuned the crystal packings and thus influenced the phase-transition points and types. The variable-temperature X-ray diffraction data for crystal 1 revealed the occurrence of a phase transition in the high-temperature phase with the space group of P21/c and in the low-temperature phase with the space group of P21/n. Crystal 2 exhibited the same space group P21/c at different temperatures. The results indicated that crystals 1 and 2 both underwent an iso-structural phase transition.

X-Ray Diffraction Study of the Phase Transition of the ${\rm Si}(111)(\sqrt{3} \times \sqrt{3})\mbox{-Ag}$ Surface

2003 ◽  
Vol 10 (02n03) ◽  
pp. 519-524 ◽  
Author(s):  
Toshio Takahashi ◽  
Hiroo Tajiri ◽  
Kazushi Sumitani ◽  
Koichi Akimoto ◽  
Hiroshi Sugiyama ◽  
...  
Keyword(s):  
Phase Transition ◽  
Transition Temperature ◽  
Low Temperatures ◽  
Diffuse Scattering ◽  
Room Temperature ◽  
Bragg Reflection ◽  
Grazing Incidence ◽  
X Ray Diffraction ◽  
X Ray ◽  
Displacive Phase Transition

The structure of the [Formula: see text] surface was studied at both room temperature and a low temperature of 50 K using grazing incidence X-ray diffraction. At low temperatures diffuse scattering was observed in addition to Bragg reflection. Least squares analyses for Bragg reflections using anisotropic Debye–Waller factors show that the structure at 50 K is consistent with an inequivalent triangle (IET) model, while the structure at room temperature is explained by a honeycomb-chained triangle (HCT) model with strong anisotropic Debye–Waller factors. From the temperature dependence of diffuse scattering, the phase transition temperature Tc and critical exponent β were determined to be about 150 K and 0.27. Some Bragg intensities showed discontinuous changes in their first derivatives at Tc. The results favor a displacive phase transition rather than an order–disorder one.

Commensurate-Glass Phase Transitions in Staged Sbcl5-GIC

1982 ◽  
Vol 20 ◽  
Author(s):  
L. Salamanca-Riba ◽  
G. Timp ◽  
L.W. Hobbs ◽  
M.S. Dresselhaus
Keyword(s):  
Phase Transition ◽  
Experimental Study ◽  
Glass Transition ◽  
Phase Transitions ◽  
Electron Diffraction ◽  
Low Temperatures ◽  
Glass Phase ◽  
Driving Mechanism ◽  
X Ray Diffraction ◽  
X Ray

ABSTRACTAn experimental study is reported of the commensurate (√7 × √7)R19.1° to glass phase transition in stages I < n > 4 graphite-SbCl5 using electron and x-ray diffraction. The electron diffraction studies show an in-plane phase transition to a glass at low temperatures. The (00l) x-ray diffraction scans show that the c-axis layered structure of the intercalate is unchanged by the phase transition. A driving mechanism for the commensurate to glass transition is suggested.

Low- and high-temperature structures of YbCuBi

2006 ◽  
Vol 221 (5-7) ◽  
Author(s):  
Andriy V. Tkachuk ◽  
Yurij Mozharivskyj ◽  
Arthur Mar
Keyword(s):  
Phase Transition ◽  
High Temperature ◽  
Intermetallic Compound ◽  
Single Crystal ◽  
Diffraction Study ◽  
Low Temperatures ◽  
Variable Temperature ◽  
X Ray Diffraction ◽  
X Ray

AbstractA variable temperature single-crystal X-ray diffraction study was undertaken on the intermetallic compound YbCuBi, which undergoes a phase transition at ∼375 K. At low temperatures (

Crystal structure and structural phase transition in bismuth-containing HoFe3(BO3)4 in the temperature range 11–500 K

2019 ◽  
Vol 75 (6) ◽  
pp. 954-968 ◽  
Author(s):  
Ekaterina S. Smirnova ◽  
Olga A. Alekseeva ◽  
Alexander P. Dudka ◽  
Dmitry N. Khmelenin ◽  
Kirill V. Frolov ◽  
...  
Keyword(s):  
Phase Transition ◽  
Structural Phase Transition ◽  
Structural Phase ◽  
Local Environment ◽  
Atomic Displacement ◽  
X Ray Diffraction ◽  
Space Group ◽  
X Ray ◽  
Atomic Displacement Parameters ◽  
Thermal Vibrations

An accurate single-crystal X-ray diffraction study of bismuth-containing HoFe3(BO3)4 between 11 and 500 K has revealed structural phase transition at T str = 365 K. The Bi atoms enter the composition from Bi2Mo3O12-based flux during crystal growth and significantly affect T str. The content of Bi was estimated by two independent methods, establishing the composition as (Ho0.96Bi0.04)Fe3(BO3)4. In the low-temperature (LT) phase below T str the (Ho0.96Bi0.04)Fe3(BO3)4 crystal symmetry is trigonal, of space group P3121, whereas at high temperature (HT) above 365 K the symmetry increases to space group R32. There is a sharp jump of oxygen O1 (LT) and O2 (LT) atomic displacement parameters (ADP) at T str. O1 and O2 ADP ellipsoids are the most elongated over 90–500 K. In space group R32 specific distances decrease steadily or do not change with decreasing temperature. In space group P3121 the distortion of the polyhedra Ho(Bi)O6, Fe1O6 and Fe2O6, B2O3 and B3O3 increases with decreasing temperature, whereas the triangles B1O3 remain almost equilateral. All BO3 triangles deviate from the ab plane with decreasing temperature. Fe–Fe distances in Fe1 chains decrease, while distances in Fe2 chains increase with decreasing temperature. The Mössbauer study confirms that the FeO6 octahedra undergo complex dynamic distortions. However, all observed distortions are rather small, and the general change in symmetry during the structural phase transition has very little influence on the local environment of iron in oxygen octahedra. The Mössbauer spectra do not distinguish two structurally different Fe1 and Fe2 positions in the LT phase. The characteristic temperatures of cation thermal vibrations were calculated using X-ray diffraction and Mössbauer data.

Magnetic Phase Transition in the Csci Fesi Spacer in Fe/FeSi Multilayers

1995 ◽  
Vol 382 ◽  
Author(s):  
J. Dekoster ◽  
A. Vantomme ◽  
S. Degroote ◽  
R. Moons ◽  
G. Langouche
Keyword(s):  
Phase Transition ◽  
Magnetic Properties ◽  
Magnetic Phase Transition ◽  
Low Temperatures ◽  
Magnetic Phase ◽  
Ferromagnetic Coupling ◽  
X Ray Diffraction ◽  
X Ray ◽  
Ion Channeling ◽  
Spacer Layer

ABSTRACTWe report the formation of the CsCI FeSi phase in Fe/FeSi multilayers with constant Fe thickness and varying FeSi layer thickness. The crystallographic and magnetic properties of this metastable FeSi phase are determined in thick (62 nm) epitaxial silicide layers with ion channeling, X-ray diffraction and Mossbauer spectroscopy measurements which clearly show that the CsCl phase becomes increasingly magnetic upon cooling down to 4.2 K. These results indicate that the transition from antiferromagnetic to ferromagnetic coupling observed at low temperatures in such multilayers is controlled by a magnetic phase transition in the FeSi spacer layer.

ANOMALIES OF CELL PARAMETERS BEFORE SUPERCONDUCTING TRANSITION FOR BISMUTH BASED OXIDE SUPERCONDUCTOR

1989 ◽  
Vol 03 (09) ◽  
pp. 685-693 ◽  
Author(s):  
S.L. YUAN ◽  
W.Y. GUAN ◽  
Z.J. CHEN ◽  
Y.L. HUANG ◽  
Y.B. JIA ◽  
...  
Keyword(s):  
Phase Transition ◽  
Diffraction Analysis ◽  
Low Temperatures ◽  
Structural Phase ◽  
Oxide Superconductors ◽  
Superconducting Transition ◽  
Oxide Superconductor ◽  
X Ray Diffraction ◽  
X Ray ◽  
Cell Parameters

The results of X-ray diffraction analysis at low temperatures for bismuth-based high-Tc oxide superconductors are reported in this letter. There is no significant structural phase transition during superconducting transition. However, it appears that the cell parameters change anomalously before superconducting transition. This anomalous change in cell parameters is repeated for different bismuth-based high-Tc oxide superconductors.

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