Order-Disorder Phase Transition in NaBD4

2004 ◽  
Vol 443-444 ◽  
pp. 287-290 ◽  
Author(s):  
P. Fischer ◽  
Andreas Züttel
Keyword(s):  
Crystal Structure ◽  
Phase Transition ◽  
Low Temperature ◽  
Neutron Diffraction ◽  
Room Temperature ◽  
Structure Model ◽  
Space Group ◽  
Disorder Phase Transition ◽  
Low Temperature Crystal Structure ◽  
Disorder Type

By means of neutron diffraction the low-temperature crystal structure of NaBD4 has been determined. At 10 K the lattice parameters are a = 4.332(1) Å and c = 5.869(1) Å. Deuterium is found in a tetrahedral arrangement [sites (8g)] around B. The symmetry corresponds to space group P42/nmc. For room temperature the structure model for NaBD4 of Davis and Kennard with disordered deuterium distributed over two sites has been revised to space group Fm-3 m. Thus the 190 K phase transition known from specific heat measurements is of order-disorder type, caused by reorientations of BD4 tetrahedra.

Investigation of the Cs x Rb1−x TiOAsO4 Series. I. Crystal Structure Analysis and Pseudo-symmetry

1998 ◽  
Vol 54 (5) ◽  
pp. 635-644 ◽  
Author(s):  
M. N. Womersley ◽  
P. A. Thomas ◽  
D. L. Corker
Keyword(s):  
Crystal Structure ◽  
Phase Transition ◽  
Low Temperature ◽  
Room Temperature ◽  
Structural Changes ◽  
Crystal Structure Analysis ◽  
Orthorhombic Space Group ◽  
Acta Cryst ◽  
Space Group ◽  
Structural Framework

Refinements of five crystals in the Cs2x Rb2−2x Ti2O2As2O8 series, caesium rubidium titanyl arsenate, with x = 0.07, 0.31, 0.58, 0.71 and 0.86, which are compositional analogues of KTiOPO4 (KTP), have been completed at 293 K and two (x = 0.71, 0.86) at low temperature. All the structures are found to be orthorhombic (space group Pna21) and are isostructural with KTP, although there is evidence of some Cs disorder over additional sites in the framework, particularly at the Cs-rich end of the series, as discussed in Part II [Thomas & Womersley (1998). Acta Cryst. B54, 645–651]. Unusually large U 33 parameters for shared Cs/Rb sites are observed and are shown to be the result of the existence of separate sites for Cs and Rb within the structural framework, although the coordinates of these sites cannot be resolved convincingly. The structural changes in the TiO6/AsO4 framework required to accommodate an increasing fraction of the larger Cs cation across the series and under cooling to 120 K are elucidated. Finally, the deviations of the room-temperature and low-temperature structures from the high-temperature prototypic structure (space group Pnan) are examined and suggest that the phase-transition temperature should increase linearly from CsTiOAsO4 to RbTiOAsO4.

NQR and Crystal Structure of 4,5-Dichloroimidazole, C3H2N2Cl2

1992 ◽  
Vol 47 (1-2) ◽  
pp. 177-181 ◽  
Author(s):  
Shi-Qi Dou ◽  
Alarich Weiss
Keyword(s):  
Crystal Structure ◽  
Phase Transition ◽  
Temperature Dependence ◽  
Room Temperature ◽  
Unit Cell ◽  
Space Group ◽  
Temperature Range ◽  
Temperature Coefficients ◽  
Group D

AbstractThe two line 35Cl NQR spectrum of 4,5-dichloroimidazole was measured in the temperature range 77≦ T/K ≦ 389. The temperature dependence of the NQR frequencies conforms with the Bayer model and no phase transition is indicated in the curves v ( 35Cl)= f(T). Also the temperature coefficients of the 35Cl NQR frequencies are "normal". At 77 K the 35Cl NQR frequencies are 37.409 MHz and 36.172 MHz and at 389 K 35.758 MHz and 34.565 MHz. The compound crystallizes at room temperature with the tetragonal space group D44-P41212, Z = 8 molecules per unit cell; at 295 K : a = 684.2(5) pm, c = 2414.0(20) pm. The relations between the crystal structure and the NQR spectrum are discussed.

scholarly journals Twinning in MAPbI3 at room temperature uncovered through Laue neutron diffraction

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
Joachim Breternitz ◽  
Michael Tovar ◽  
Susan Schorr
Keyword(s):  
Crystal Structure ◽  
Phase Transition ◽  
Neutron Diffraction ◽  
Room Temperature ◽  
Point Of View ◽  
Temperature Structure ◽  
Theoretical Point ◽  
Laue Diffraction ◽  
The Past ◽  
Halide Perovskites

Abstract The crystal structure of MAPbI3, the signature compound of the hybrid halide perovskites, at room temperature has been a reason for debate and confusion in the past. Part of this confusion may be due to twinning as the material bears a phase transition just above room temperature, which follows a direct group–subgroup relationship and is prone to twinning. Using neutron Laue diffraction, we illustrate the nature of twinning in the room temperature structure of MAPbI3 and explain its origins from a group-theoretical point-of-view.

Structural Study on Ammonia Borane for Hydrogen Storage

2009 ◽  
Vol 610-613 ◽  
pp. 425-430 ◽  
Author(s):  
W.J. James ◽  
L. Jagat ◽  
Q. Cai ◽  
W.B. Yelon ◽  
J.B. Yang
Keyword(s):  
Phase Transition ◽  
Neutron Diffraction ◽  
Hydrogen Storage ◽  
Scattering Length ◽  
Ammonia Borane ◽  
Scanning Calorimetry ◽  
Space Group ◽  
Disorder Phase Transition ◽  
Group I ◽  
Significant Difference

Ammonia borane(BH3NH3) is a promising hydrogen storage material because of its high gravimetric (19.6 wt% H2) and volumetric hydrogen density with an accompanying moderate decomposition temperature. Previously reported structures determined by using x-ray and neutron diffraction on hydrides show differences in bond lengths and atomic coordination. Here, the crystal structures of fully and half deuterated ammonia borane were investigated as a function of temperature using powder neutron diffraction. The neutron diffraction patterns show a significant difference due to large difference in the scattering length of D and H. It is evident that an order-disorder phase transition occurs around 225 K for all compounds. At low temperature, the compound crystallizes in the orthorhombic structure with space group Pnm21 and gradually transforms to a high temperature disordered tetragonal structure with space group I/4mm at about 225K. The differential scanning calorimetry studies confirm this phase transformation and also indicate that all compounds melt and decompose at above 370 K. The c cell parameter remains unchanged in the orthorhombic phase from 16 K to 200K and increases liaa nearly above 225K. As the temperature is increased, the BH3-NH3 groups start to reorient along the c axis, and the D/H atoms become disordered, leading to the tetragonal phase transition around 225K.

Low-temperature crystal structure of RS-thiocamphor

2004 ◽  
Vol 219 (9) ◽  
Author(s):  
E. Louise R. Robins ◽  
Michela Brunelli ◽  
Asiloé J. Mora ◽  
Andrew N. Fitch
Keyword(s):  
Crystal Structure ◽  
Phase Transitions ◽  
Low Temperature ◽  
Room Temperature ◽  
Cubic Phase ◽  
X Ray Diffraction ◽  
Orthorhombic Space Group ◽  
Two Phase ◽  
X Ray ◽  
Low Temperature Crystal Structure

AbstractDSC and high-resolution powder X-ray diffraction measurements in the range 295 K–100 K show that RS-thiocamphor undergoes two phase transitions. The first, at around 260 K on cooling, is from the room-temperature body-centred-cubic phase to a short-lived intermediate. At 258 K the low-temperature form starts to appear. The crystal structure of the latter is orthorhombic, space group

scholarly journals The low-temperature triclinic crystal structure of silver 3-sulfobenzoic acid

2020 ◽  
Vol 76 (8) ◽  
pp. 1275-1278
Author(s):  
Reuben T. Bettinger ◽  
Philip J. Squattrito ◽  
Darpandeep Aulakh
Keyword(s):  
Crystal Structure ◽  
Phase Transition ◽  
Low Temperature ◽  
Room Temperature ◽  
Monoclinic Structure ◽  
Structure Space ◽  
Reversible Phase Transition ◽  
Triclinic Structure ◽  
Reversible Phase ◽  
Acidic Hydrogen

Poly[(μ4-3-carboxybenzenesulfonato)silver(I)], Ag(O3SC6H4CO2H) or [Ag(C7H5O5S)] n , has been found to undergo a reversible phase transition from monoclinic to triclinic between 160 and 150 K. The low-temperature triclinic structure (space group P\overline{1}) has been determined at 100 K. In contrast to the reported room temperature monoclinic structure, in which the nearly equivalent carboxylate C—O distances indicate that the acidic hydrogen is randomly distributed between the O atoms, at 100 K the C—O (protonated) and C=O (unprotonated) bonds are clearly resolved, resulting in the reduction in symmetry from C2/c to P\overline{1}.

scholarly journals Phase transition and structures of the twinned low-temperature phases of (Et4N)[ReS4]

2020 ◽  
Vol 76 (3) ◽  
pp. 231-235
Author(s):  
Eduard Bernhardt ◽  
Regine Herbst-Irmer
Keyword(s):  
Phase Transition ◽  
Low Temperature ◽  
Title Compound ◽  
Room Temperature ◽  
Monoclinic Space Group ◽  
Rapid Cooling ◽  
Space Group ◽  
Disordered Structure ◽  
Β Phase ◽  
Α Phase

The title compound, tetraethylammonium tetrathiorhenate, [(C2H5)4N][ReS4], has, at room temperature, a disordered structure in the space group P63 mc (Z = 2, α-phase). A phase transition to the monoclinic space group P21 (Z = 2, γ-phase) at 285 K leads to a pseudo-merohedral twin. The high deviation from the hexagonal metric causes split reflections. However, the different orientations could not be separated, but were integrated using a large integration box. Rapid cooling to 110–170 K produces a metastable β-phase (P63, Z = 18) in addition to the γ-phase. All crystals of the β-phase are contaminated with the γ-phase. Additionally, the crystals of the β-phase are merohedrally twinned. In contrast to the α-phase, the β- and γ-phases do not show disorder.

scholarly journals TheZ′ = 12 superstructure of Λ-cobalt(III) sepulchrate trinitrate governed by C—H...O hydrogen bonds

2016 ◽  
Vol 72 (3) ◽  
pp. 372-380 ◽  
Author(s):  
Somnath Dey ◽  
Andreas Schönleber ◽  
Swastik Mondal ◽  
Siriyara Jagannatha Prathapa ◽  
Sander van Smaalen ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Low Temperature ◽  
Hydrogen Bonds ◽  
Room Temperature ◽  
Structural Parameters ◽  
Molecular Packing ◽  
Nitrate Group ◽  
Structural Variations ◽  
Monoclinic Symmetry ◽  
Low Temperature Crystal Structure

Λ-Cobalt(III) sepulchrate trinitrate crystallizes inP6322 withZ= 2 (Z′ = 1/6) at room temperature. Slabs perpendicular to the hexagonal axis comprise molecules Co(sepulchrate) alternating with nitrate groupsAandB. Coordinated by six sepulchrate molecules, highly disordered nitrate groupsCare accommodated between the slabs. Here we report the fully ordered, low-temperature crystal structure of Co(sep)(NO3)3. It is found to be a high-Z′ structure withZ′ = 12 of the 12-fold 6a_{h}\times\sqrt{3}b_{h}\times c_{h} superstructure with monoclinic symmetryP21(cunique). Correlations between structural parameters are effectively removed by refinements within the superspace approach. Superstructure formation is governed by a densification of the packing in conjunction with ordering of nitrate groupC, the latter assuming different orientations for each of theZ′ = 12 independent copies in the superstructure. The Co(sep) moiety exhibits small structural variations over its 12 independent copies, while orientations of nitrate groupsAandBvary less than the orientations of the nitrate groupCdo. Molecular packing in the superstructure is found to be determined by short C—H...H—C contacts, with H...H distances of 2.2–2.3 Å, and by short C—H...O contacts, with H...O distances down to 2.2 Å. These contacts presumably represent weak C—H...O hydrogen bonds, but in any case they prevent further densification of the structure and strengthening of weak N—H...O hydrogen bonds with observed H...O distances of 2.4–2.6 Å.

Synthese und Kristallstrukturen von N-[ω-(Dimethylammonio)alkyl]- N´,N´,N´´,N´´-tetramethylguanidinium-chlorid-tetraphenylboraten / Synthesis and Crystal Structures of N-[ω-(Dimethylammonio)alkyl]-N´,N´,N´´,N´´- tetramethylguanidinium Chloride Tetraphenylborates

2010 ◽  
Vol 65 (7) ◽  
pp. 907-916 ◽  
Author(s):  
Ioannis Tiritiris ◽  
Falk Lissner ◽  
Thomas Schleid ◽  
Willi Kantlehner
Keyword(s):  
Crystal Structure ◽  
Low Temperature ◽  
Hydrogen Bonds ◽  
Crystal Structures ◽  
Room Temperature ◽  
Chloride Ions ◽  
Monoclinic Space Group ◽  
Temperature Structure ◽  
Space Group ◽  
Temperature Modification

Dicationic N,N´,N´,N´´,N´´-pentasubstituted guanidinium dichlorides 4a, b are obtained from the chloroformamidinium salt 2 and diamines 3a, b. N-[2-(Dimethylammonio)ethyl]-N´,N´,N´´,N´´-tetramethylguanidinium chloride tetraphenylborate (5a) and N-[3-(dimethylammonio)propyl]-N´,N´,N´´,N´´-tetramethylguanidinium chloride tetraphenylborate (5b) were synthesized from 4a, b by anion metathesis with one equivalent of sodium tetraphenylborate. The thermal properties of the salts 5a, b were studied by means of DSC methods, and their crystal structures were determined by single-crystal X-ray diffraction analysis. For 5a a solid-solid phase transition is observed at −156 ◦C to a low-temperature structure. The room-temperature modification (α-5a) crystallizes in the centrosymmetric orthorhombic space group Pbca (a = 13.1844(4), b = 13.8007(4), c = 34.7537(11) A° ).The guanidinium ions are interconnected via chloride ions through bridging N-H· · ·Cl hydrogen bonds, providing isolated units. The tetraphenylborate ions show some dynamic disordering in the crystal structure. The low-temperature modification (β -5a) also crystallizes orthorhombically, but in the non-centrosymmetric space group Pna21 (a = 13.1099(4), b = 69.1810(11), c = 13.5847(5) A° ) and consists of four crystallographically independent cations and anions in the unit cell. Compared with the room-temperature structure, a similar N-H· · ·Cl hydrogen bond pattern is observed in the β -phase, but the tetraphenylborate ions are now completely ordered. 5b crystallizes in the monoclinic space group P21/c (a = 10.8010(3), b = 14.1502(5), c = 20.9867(9) A° , β = 94.322(1)◦). In the crystal structure the guanidinium ions are linked via chloride ions through N-H· · ·Cl hydrogen bonds, but in contrast to 5a two infinite strands are formed along the a axis with the tetraphenylborate ions interspersed between them for charge compensation.

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