scholarly journals Growth-induced incommensurability observed in the organic co-crystal hexamethylenetetramine resorcinol

2006 ◽  
Vol 62 (6) ◽  
pp. 1043-1050 ◽  
Author(s):  
Soraya Maria Belluga Rodriguez ◽  
Lukáš Palatinus ◽  
Václav Petříček ◽  
Gervais Chapuis
Keyword(s):  
Phase Transition ◽  
Poor Quality ◽  
Temperature Phase ◽  
X Ray Diffraction ◽  
Modulated Structure ◽  
Main Effect ◽  
Harmonic Modulation ◽  
Low Temperature Phase ◽  
Modulation Vector

Co-crystals of hexamethylenetetramine and resorcinol were investigated by X-ray diffraction. The structure was refined in the superspace group Xmcm(0\beta 0)s0s, X = (\,{{1}\over{2}} {{1}\over{2}} 0 {{1}\over{2}}\,). In the average structure the resorcinol molecules are disordered between two orientations. The main effect of the modulation in the structure is a harmonic modulation of the occupation probabilities of the two orientations of the resorcinol molecule. However, the modulated order is not perfect and the resorcinol molecules remain partially disordered. Below 270 K the crystal undergoes a phase transition to a commensurately modulated structure with modulation vector {\bf q} = (0 {{1}\over{2}} {{1}\over{4}}\,) and superspace group X2/m(0\beta \gamma)0s. The structure of the low-temperature phase could not be determined owing to the poor quality of the crystals affected by the reconstructive phase transition.

X-ray diffraction study of the phase transition of K2Mn2(BeF4)3: a new type of low-temperature structure for langbeinites

2001 ◽  
Vol 57 (3) ◽  
pp. 221-230 ◽  
Author(s):  
A. Guelylah ◽  
G. Madariaga ◽  
V. Petricek ◽  
T. Breczewski ◽  
M. I. Aroyo ◽  
...  
Keyword(s):  
Phase Transition ◽  
Low Temperature ◽  
Mode Analysis ◽  
Cubic Phase ◽  
Temperature Phase ◽  
Temperature Structure ◽  
X Ray Diffraction ◽  
X Ray ◽  
New Type ◽  
Low Temperature Phase

The potassium manganese tetrafluoroberyllate langbeinite compound has been studied in the temperature range 100–300 K. Using DSC measurements, a phase transition has been detected at 213 K. The space group of the low-temperature phase was determined to be P1121 using X-ray diffraction experiments and optical observations of the domain structure. The b axis is doubled with respect to the prototypic P213 cubic phase. Lattice parameters were determined by powder diffraction data [a = 10.0690 (8), b = 20.136 (2), c = 10.0329 (4) Å, γ = 90.01 (1)°]. A precise analysis of the BeF4 tetrahedra in the low-temperature phase shows that two independent tetrahedra rotate in opposite directions along the doubled crystallographic axis. A symmetry mode analysis of the monoclinic distortion is also reported. This is the first report of the existence of such a phase transition in K2Mn2(BeF4)3 and also of a new type of low-temperature structure for langbeinite compounds.

Crystal Structure and Phase Transition of 4-Aminopyridinium Tetrabromoantimonate(III) as Studied by Bromine and Antimony NQR, Proton NMR, and Single Crystal X-Ray Diffraction

2000 ◽  
Vol 55 (1-2) ◽  
pp. 167-172 ◽  
Author(s):  
Masao Hashimoto ◽  
Shinichi Hashimoto ◽  
Hiromitsu Terao ◽  
Masayuki Kuma ◽  
Haruo Niki ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Phase Transition ◽  
Monoclinic Space Group ◽  
Temperature Phase ◽  
X Ray Diffraction ◽  
Reorientational Motion ◽  
H Nmr ◽  
Crystal Dynamics ◽  
Motional Narrowing ◽  
Low Temperature Phase

The crystal structure of the room temperature phase (RTP) of the title compound was determined at 297 K (monoclinic, space group C2/c, a = 1384.2(2), b = 1377.8(3), c = 755.5(2) pm, β = 121.58(1)°). A complicated disorder was found for the cation. A phase transition from the low-temperature phase (LTP) to the RTP was found at (224 ±1) K (Tc). The 1H NMR spectra showed a sharp motional narrowing at ca. T=Tc , indicating the occurrence of a reorientational motion of the cation in the RTP in accord with the disorder. It was found that another reorientational motion is excited in the LTP. Four 81Br NQR lines (132.71, 115.38, 61.54 and 59.31 MHz at 77 K) and two Sb NQR lines (53.78 and 33.76 MHz at 77 K) were found in the LTP, while a single 81Br NQR line was observed at T> 276 K (ca. 121.80 MHz at 300 K). Crystal dynamics are discussed on the basis of the temperature dependence of the NQR, 1H NMR line width, and 1H NMR T1.

Phase Transitions and Distortion of [BiCl6]3– Octahedra in (C3H5NH3)3[BiCl6] – DSC and Single-Crystal X-Ray Diffraction Studies

2004 ◽  
Vol 59 (9) ◽  
pp. 1029-1034 ◽  
Author(s):  
Bartosz Zarychta ◽  
Maciej Bujak ◽  
Jacek Zaleski
Keyword(s):  
Phase Transition ◽  
High Temperature Phase ◽  
Temperature Phase ◽  
X Ray Diffraction ◽  
X Ray ◽  
Unit Cells ◽  
Temperature Phase Transition ◽  
The Relationship ◽  
Low Temperature Phase ◽  
Disorder Type

The DSC diagram of tris(allylammonium) hexachlorobismuthate(III), (C3H5NH3)3[BiCl6], revealed three anomalies at 152, 191 and 299 K. The structure of the salt was determined at 200 and 315 K, below and above the high-temperature phase transition at 299 K. In both phases the crystals are monoclinic. At 200 K the space group is C2/c whereas at 315 K it is C2/m. The structures, at both temperatures, are composed of [BiCl6]3− octahedra and allylammonium cations. The organic and inorganic moieties are attracted to each other by a network of the N-H. . .Cl hydrogen bonds. The relationship between corresponding parameters of the unit cells has been found. The phase transition at 299 K, of the order-disorder type, is attributed to the ordering of one non-equivalent allylammonium cation in the low-temperature phase.

Preparation, Crystal Structure at 298 and 90 K and Phase Transition in (C2H5NH3)2[SbBr5] Studied by the Single Crystal X-Ray Diffraction Method

2004 ◽  
Vol 59 (3) ◽  
pp. 298-304 ◽  
Author(s):  
Maciej Bujak ◽  
Bartosz Zarychta ◽  
Aleksandra Kobel ◽  
Jacek Zaleski
Keyword(s):  
Phase Transition ◽  
Diffraction Method ◽  
Temperature Phase ◽  
X Ray Diffraction ◽  
Methyl Carbon ◽  
One Dimensional ◽  
Space Groups ◽  
Molar Ratios ◽  
Low Temperature Phase ◽  
Disorder Type

The reaction of antimony(III) oxide with ethylamine, in molar ratios from 1:1 to 1:10, in concentrated hydrobromic acid leads to the formation of one product - bis(ethylammonium) pentabromoantimonate( III). The structure of (C2H5NH3)2[SbBr5] was determined at 298 and 90 K, below and above the phase transition that occurs at about 158.5 K. The orthorhombic system was found in both phases, space groups Cmca and Pbca at 298 and 90 K, respectively. At both temperatures the structure consists of [SbBr6]3− octahedra connected via cis bromine atoms forming one-dimensional zig-zag [{SbBr5}2−]n chains. The ethylammonium cations fill the space between polyanionic chains. The organic and inorganic substructures are held together by a system of N(-H)···Br interactions. Their influence on the deformation of [SbBr6]3− octahedra is well reflected in differences in the corresponding Sb-Br bond lengths and Br-Sb-Br angles in both phases. The phase transition is of the first order and the order-disorder type. It is related to changes in the molecular dynamics of the ethylammonium cations. In the low-temperature phase the organic cations are ordered, while at 298 K both crystallographically independent cations are disordered. The type of disorder is realized by the presence of two positions of the methyl carbon atoms

NQR View of Solid Phases of NOCl

1998 ◽  
Vol 53 (6-7) ◽  
pp. 537-541 ◽  
Author(s):  
J. Pirnat ◽  
Z. Trontelj ◽  
H. Borrmann
Keyword(s):  
Phase Transition ◽  
Temperature Phase ◽  
Measured Temperature ◽  
X Ray Diffraction ◽  
X Ray ◽  
Disorder Phase Transition ◽  
Upper Limit ◽  
Temperature Phase Transition ◽  
Solid Phases ◽  
Low Temperature Phase

Abstract Chlorine NQR studies of solid nitrosyl chloride NOC1 between 110 and 212 K are reported. In the temperature dependence an order-disorder phase transition near 145 K, found by X-ray diffraction, is confirmed. Unusual hysteretic NQR signal behaviour indirectly proves also the low temperature phase transition below 100 K. In the measured temperature region fast relaxing mechanisms are present. The upper limit of the expected 14N NQR frequency is estimated using the Townes-Dailey approach.

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.

scholarly journals Direct observation of excitonic instability in Ta2NiSe5

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Kwangrae Kim ◽  
Hoon Kim ◽  
Jonghwan Kim ◽  
Changil Kwon ◽  
Jun Sung Kim ◽  
...  
Keyword(s):  
Phase Transition ◽  
Direct Observation ◽  
Structural Phase ◽  
Temperature Phase ◽  
Phonon Coupling ◽  
Strong Electron ◽  
Weiss Temperature ◽  
Excitonic Insulator ◽  
Electron Phonon Coupling ◽  
Low Temperature Phase

AbstractCoulomb attraction between electrons and holes in a narrow-gap semiconductor or a semimetal is predicted to lead to an elusive phase of matter dubbed excitonic insulator. However, direct observation of such electronic instability remains extremely rare. Here, we report the observation of incipient divergence in the static excitonic susceptibility of the candidate material Ta2NiSe5 using Raman spectroscopy. Critical fluctuations of the excitonic order parameter give rise to quasi-elastic scattering of B2g symmetry, whose intensity grows inversely with temperature toward the Weiss temperature of TW ≈ 237 K, which is arrested by a structural phase transition driven by an acoustic phonon of the same symmetry at TC = 325 K. Concurrently, a B2g optical phonon becomes heavily damped to the extent that its trace is almost invisible around TC, which manifests a strong electron-phonon coupling that has obscured the identification of the low-temperature phase as an excitonic insulator for more than a decade. Our results unambiguously reveal the electronic origin of the phase transition.

Sign in / Sign up

Export Citation Format

Share Document