Structural Phase Transition in Tetrafluoroaluminates

1982 ◽  
Vol 21 ◽  
Author(s):  
J.M. Launay ◽  
J.Y. Laval ◽  
A. Gibaud ◽  
A. Bulou ◽  
J. Nouet
Keyword(s):  
Electron Diffraction ◽  
Room Temperature ◽  
Structural Phase ◽  
The Other ◽  
Electron Diffraction Data ◽  
Temperature Phase ◽  
X Ray ◽  
Quadratic Phase ◽  
Low Temperature Phase ◽  
Good Agreement

ABSTRACTIt is shown that the detailed investigation of an irreversible SPT implies the combination of X-ray, neutron and electron diffraction data. This diffraction analysis is applied to K Al F4 and Rb Al F4. There is a good agreement between the three diffraction techniques in the case of Rb Al F4 where the SPT is reversible. On the other hand, for K Al F4 room temperature quadratic phase, electron diffraction exhibits exta spots which are not evidenced by X-ray and neutron diffraction. Finally the assumption of an orthorombic lattice from neutron scattering for the low temperature phase is consistant with electron diffraction results.

Single-Crystal X-Ray Scattering Study of Superstructures and Phase Transitions in Graphite-Hno3 and Graphite-Br2 Intercalation Compounds

1982 ◽  
Vol 20 ◽  
Author(s):  
R. Moret ◽  
R. Comes ◽  
G. Furdin ◽  
H. Fuzellier ◽  
F. Rousseaux
Keyword(s):  
Phase Transitions ◽  
Low Temperature ◽  
Room Temperature ◽  
Temperature Phase ◽  
Temperature Structure ◽  
X Ray ◽  
X Ray Scattering ◽  
Scattering Study ◽  
Temperature Liquid ◽  
Low Temperature Phase

ABSTRACTIn α-C5n-HNO3 the condensation of the room-temperature liquid-like diffuse ring associated with the disorder-order transition around 250 K is studied and the low-temperature. superstructure is examined.It is found that β-C8n-HNO3 exhibits an in-plane incommensurate order at room temperature.Two types of graphite-Br2 are found. Low-temperature phase transitions in C8Br are observed at T1 ≍ 277 K and T2 ≍ 297 K. The room-temperature structure of C14Br is reexamined. Special attention is given to diffuse scattering and incommensurability.

Structural phase transition to disorder low-temperature phase in [Fe(ptz)6](BF4)2 spin-crossover compounds

2012 ◽  
Vol 68 (1) ◽  
pp. 40-56 ◽  
Author(s):  
Joachim Kusz ◽  
Maciej Zubko ◽  
Reinhard B. Neder ◽  
Phillipp Gütlich
Keyword(s):  
Short Range ◽  
Short Range Order ◽  
Spin Crossover ◽  
Structural Phase ◽  
The Other ◽  
Special Technique ◽  
Temperature Phase ◽  
Disordered Phase ◽  
Novel Approach ◽  
Low Temperature Phase

In the spin-crossover compound [Fe(ptz)6](BF4)2 (where ptz=1-n-propyltetrazole) six different phases are observed. When a single crystal is slowly cooled from high temperatures to those below 125 K, the reflections broaden into diffuse maxima and split into two maxima along the c* direction [Kusz, Gütlich & Spiering (2004). Top. Curr. Chem. 234, 129–153]. As both maxima are broad along the c* direction, the short-range order exists only along the c direction and in the ab plane the structure remains long-range ordered. In this disordered phase additional satellite reflections appear. Upon heating above 135 K, the diffuse maxima return to their previous shape and this process is completely reversible. Rapidly cooled samples, on the other hand, do not show such splitting and the symmetry remains R\bar 3, despite a jump in lattice parameters. We use a special technique to analyse the disorder model of the slowly cooled samples, which consists of layered domains shifted in the hexagonal ab plane. The low-spin disordered phase was solved in a novel approach to accommodate the very unusual twinning and refined in the non-standard space group C\bar 1. In contrast to the ordered low-spin phase, the Fe ion is in a non-centrosymmetric coordination polyhedron and two of the six propyl groups change their conformation.

Differences and similarities among hypoxanthinium nitrate hydrate structures

2019 ◽  
Vol 75 (8) ◽  
pp. 1036-1044 ◽  
Author(s):  
Małgorzata Katarzyna Cabaj ◽  
Roman Gajda ◽  
Anna Hoser ◽  
Anna Makal ◽  
Paulina Maria Dominiak
Keyword(s):  
Room Temperature ◽  
Temperature Phase ◽  
X Ray Diffraction ◽  
Acta Cryst ◽  
X Ray ◽  
Nitrate Hydrate ◽  
Different Temperatures ◽  
Lower Temperature ◽  
Low Temperature Phase ◽  
Nitrate Anions

Crystals of hypoxanthinium (6-oxo-1H,7H-purin-9-ium) nitrate hydrates were investigated by means of X-ray diffraction at different temperatures. The data for hypoxanthinium nitrate monohydrate (C5H5N4O+·NO3 −·H2O, Hx1) were collected at 20, 105 and 285 K. The room-temperature phase was reported previously [Schmalle et al. (1990). Acta Cryst. C46, 340–342] and the low-temperature phase has not been investigated yet. The structure underwent a phase transition, which resulted in a change of space group from Pmnb to P21/n at lower temperature and subsequently in nonmerohedral twinning. The structure of hypoxanthinium dinitrate trihydrate (H3O+·C5H5N4O+·2NO3 −·2H2O, Hx2) was determined at 20 and 100 K, and also has not been reported previously. The Hx2 structure consists of two types of layers: the `hypoxanthinium nitrate monohydrate' layers (HX) observed in Hx1 and layers of Zundel complex H3O+·H2O interacting with nitrate anions (OX). The crystal can be considered as a solid solution of two salts, i.e. hypoxanthinium nitrate monohydrate, C5H5N4O+·NO3 −·H2O, and oxonium nitrate monohydrate, H3O+(H2O)·NO3 −.

A thermal and X-ray investigation of scarbroite

1960 ◽  
Vol 32 (248) ◽  
pp. 353-362 ◽  
Author(s):  
W. J. Duffin ◽  
J. Goodyear
Keyword(s):  
Electron Diffraction ◽  
Chemical Analysis ◽  
Diffraction Data ◽  
Room Temperature ◽  
Layer Structure ◽  
Electron Diffraction Data ◽  
X Ray ◽  
Fine Grained ◽  
The North

SummaryScarbroite, a fine-grained but compact deposit obtained from fissures in the sandstone on the north Yorkshire coast, is shown by chemical analysis to have an idealized formula Al2(CO3)3·12Al(OH)3. X-ray and electron diffraction data indicate a triclinic cell with a 9·94 Å., b 14·88 Å., c 26·47 Å., α 98·7°, β 96·5°, and γ 89·0°. A layer structure consisting of gibbsite-type sheets of Al(OH)3 and sheets of Al2(CO3)3 is proposed. The structure is stable from room temperature to about 125° C.

Substitution Effect in the Ion Conductor Li3InBr6, Studied by Nuclear Magnetic Resonance

2002 ◽  
Vol 57 (6-7) ◽  
pp. 447-450 ◽  
Author(s):  
Yasumasa Tomita ◽  
Hiroshi Yonekura ◽  
Yasuo Yamauchi ◽  
Koji Yamada ◽  
Kenkichiro Kobayashi
Keyword(s):  
Nmr Spectra ◽  
Substitution Effect ◽  
The Other ◽  
Temperature Phase ◽  
Cation Substitution ◽  
Ion Conductor ◽  
X Ray ◽  
Lattice Constants ◽  
Low Temperature Phase ◽  
Cation Substitution Effect

Li3-2x Mg InBr6 (x= 0.02 - 0.4) was synthesized, and the cation substitution effect on the conductivity was investigated by means of 7Li and 115In NMR, and X-ray diffraction.With increasing x the lattice constants a and c increased, but b and β did not show significant changes. The conductivity of the low temperature phase increased with x, associated with a narrowing of the 7Li NMR spectra. In the high temperature superionic phase, on the other hand, the conductivity decreased with x accompanied by a broadening of the 115In NMR spectra

Structure at 200 and 298 K and X-ray investigations of the phase transition at 242 K of [NH2(CH3)2]3Sb2Cl9 (DMACA)

1996 ◽  
Vol 52 (2) ◽  
pp. 287-295 ◽  
Author(s):  
J. Zaleski ◽  
A. Pietraszko
Keyword(s):  
Crystal Structure ◽  
Phase Transition ◽  
Hydrogen Bonds ◽  
Room Temperature ◽  
Lone Electron Pair ◽  
Electron Pair ◽  
Temperature Phase ◽  
Space Group ◽  
X Ray ◽  
Low Temperature Phase

[NH2(CH3)2]3Sb2Cl9 (dimethylammonium nonachlorodiantimonate, DMACA) has, at 200 K, a monoclinic Pc space group, with a = 9.470 (3), b = 9.034 (3), c = 14.080 (4) Å, β = 95.81 (3)°, V = 1198.4 (4) Å3, Z = 2 [R = 0.024, wR = 0.025 for 4613 independent reflections with F > 4σ(F)]. At 298 K DMACA has P21/c space group with a = 9.686 (3), b = 9.037 (3), c = 14.066 (4) Å, β = 95.57 (3)°, V = 1225.3 (5) Å3, Z = 2 [R = 0.034, wR = 0.035 for 2736 reflections with F > 4σ(F)]. The anionic sublattice of DMACA consists of polyanionic (Sb2Cl9 3−), layers. In the low-temperature phase there are three crystallographically non-equivalent dimethylammonium cations in the crystal structure. One of the cations is located inside the polyanionic layers, two others – one ordered and one disordered – between the polyanionic layers. In the room-temperature phase there are two non-equivalent cations – both disordered – in the crystal structure. Temperature dependencies of lattice parameters between 200 and 300 K were determined. The occurrence of a second-order phase transition at T = 242 K was confirmed. The dependence of lengths of Sb—Cl contacts on the presence and strength of N—H...CI hydrogen bonds was discussed. It was found that lengths of Sb—Cl bonds may differ from each other by as much as 0.3 Å, because of the presence of N—H...Cl hydrogen bonds. These differences were attributed to distortion of the lone-electron pair on antimony(Ill).

scholarly journals Structure and pseudosymmetry of cholesterol at 310 K

2002 ◽  
Vol 58 (2) ◽  
pp. 260-264 ◽  
Author(s):  
Leh-Yeh Hsu ◽  
Jeff W. Kampf ◽  
Christer E. Nordman
Keyword(s):  
Phase Transition ◽  
Room Temperature ◽  
Unit Cell ◽  
The Other ◽  
Temperature Phase ◽  
Triclinic Space Group ◽  
Space Group ◽  
X Ray ◽  
Cell Parameters

The structure of cholesterol above the (304.8 K) phase transition, previously published in preliminary form [Hsu & Nordman (1983). Science, 220, 604–606], has been fully refined using augmented X-ray data. The crystals are triclinic, space group P1, with (reassigned) cell parameters a = 27.565 (10), b = 38.624 (16), c = 10.748 (4) Å, α = 93.49 (3), β = 90.90 (3), γ = 117.15 (3)°, and V = 10151 (7) Å3. The unit cell contains Z = 16 molecules, of which eight are related to the other eight by unusual twofold rotational pseudosymmetry. The structure is related to the room-temperature phase, with Z = 8, by a rearrangement of some of the molecules, and by a doubling of the a axis.

Electron diffraction study of the space group of Bi5Ti3FeO15 multiferroic ceramic

2020 ◽  
Vol 76 (5) ◽  
pp. 454-457
Author(s):  
Ying Zheng ◽  
Xinyan Wu ◽  
Yongcheng Zhang ◽  
Weiquan Shao ◽  
Wanneng Ye
Keyword(s):  
Electron Diffraction ◽  
Room Temperature ◽  
Electron Diffraction Study ◽  
Temperature Phase ◽  
X Ray Diffraction ◽  
Space Group ◽  
X Ray ◽  
Space Groups ◽  
Phase Compound ◽  
First Time

Bi5Ti3FeO15 (pentabismuth trititanium iron pentadecaoxide), which is a multiferroic four-layer Aurivillius phase compound, has received much attention in recent years. However, three mutually inconsistent orthorhombic space groups, i.e. A21 am, Fmm2 and Pnn2, have been reported for the room-temperature phase of Bi5Ti3FeO15 by X-ray and neutron diffraction investigations. Here, electron diffraction results are presented and discussed for the first time to unambiguously clarify the room-temperature space group of ceramic Bi5Ti3FeO15. It has been found that all the observed reflections from the ceramic agree with those expected in A21 am, while the observed reflections 011, 013 and 015 should be forbidden in the case of Fmm2, and no 107 and 109 reflections were observed although allowed for Pnn2. The present study has demonstrated that the space group of Bi5Ti3FeO15 ceramic is A21 am rather than Fmm2 or Pnn2, an identification that proved to be a challenge for X-ray diffraction. On the basis of the space group A21 am, the lattice parameters of the Bi5Ti3FeO15 ceramic were calculated from its X-ray diffraction data.

scholarly journals A63,65Cu and 127I Nuclear Quadrupole Resonance and X-Ray Crystallographic Study of a Low-Temperature Phase of the (2-picoline) Copper (I) Iodide Dimer

1992 ◽  
Vol 47 (1-2) ◽  
pp. 106-116
Author(s):  
Augustin Habiyakare ◽  
Edwin A. C. Lücken ◽  
Gerald Bernardinelli
Keyword(s):  
Low Temperature ◽  
Temperature Dependence ◽  
Room Temperature ◽  
Membered Ring ◽  
Temperature Phase ◽  
X Ray ◽  
Crystallographic Study ◽  
Quadrupole Resonance ◽  
Nuclear Quadrupole ◽  
Low Temperature Phase

AbstractThe temperature-dependence of the 63Cu and 127I NQR spectra of bis(2-picoline) Copper(I) Iodide reveals the existence of a phase change at 250 K. An X-ray crystallographic study of the low-temperature phase reveals that the iodine-bridged dimeric structure, which was observed at room-temperature, is retained in the low temperature phase but that the bond-lengths and, particularly, the bond-angles of the central four-membered ring are considerably modified.

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