scholarly journals Selected solid-state behaviour of three di-tert-butyl-substituted N-salicylideneaniline derivatives: temperature-induced phase transitions and chromic behaviour

2021 ◽  
Vol 77 (10) ◽  
pp. 659-667
Author(s):  
Helen E. Mason ◽  
Judith A. K. Howard ◽  
Hazel A. Sparkes
Keyword(s):  
Phase Transition ◽  
Hydrogen Bond ◽  
Phase Transitions ◽  
Solid State ◽  
Low Temperature ◽  
Schiff Bases ◽  
Photochromic Properties ◽  
Keto Form ◽  
Single Crystal Structures ◽  
State Behaviour

The synthesis, single-crystal structures and chromic behaviour of three related Schiff bases, namely, (E)-2,4-di-tert-butyl-6-{[(4-fluorophenyl)imino]methyl}phenol, C21H26FNO, 1, (E)-2,4-di-tert-butyl-6-{[(4-chlorophenyl)imino]methyl}phenol, C21H26ClNO, 2, and (E)-6-{[(4-bromophenyl)imino]methyl}-2,4-di-tert-butylphenol, C21H26BrNO, 3, are reported. Two polymorphs of 1 were obtained, which were found to have different photochromic properties. Schiff bases 2 and 3 were found to be isostructural and underwent a phase transition upon cooling which was attributed to the dynamic disorder in one of the tert-butyl groups resolving at low temperature. All of the structures were found to exist in the enol rather than the keto form based on the C—O(H) and imine C=N bond lengths, and contained an intramolecular O—H...N hydrogen bond alongside weaker intermolecular C—H...O contacts.

Mössbauer Studies of Fe2+ in Iron Langbeinites and other Crystals with Langbeinite Structure

1998 ◽  
Vol 53 (1-2) ◽  
pp. 27-37 ◽  
Author(s):  
M. Windhaus ◽  
B. D. Mosel ◽  
W. Müller-Warmuth
Keyword(s):  
Phase Transition ◽  
Phase Transitions ◽  
High Temperature ◽  
Low Temperature ◽  
High Spin State ◽  
Cubic Phases ◽  
Debye Temperatures ◽  
Phase Transition Temperatures ◽  
Abrupt Changes ◽  
Temperature Dependences

Abstract 57 Fe Mössbauer spectra have been measured at various temperatures between 4.2 K and 300 K for iron langbeinites A 2 Fe 2^04)3 with A = K, NH 4 , Rb, T1 and magnesium, manganese and cadmium lang-beinites doped with Fe" + . The spectra revealed several contributions whose isomer shifts and quadru-pole splittings have been obtained by fitting program routines. For the high-temperature cubic phases two crystallographically non-equivalent iron sites have been identified, characteristic of Fe2+ in the high-spin state. Abrupt changes of the quadrupole couplings indicated phase transitions; in some cases, the spectra have also revealed several sites for Fe2+ in low temperature phases. From the temperature dependences, phase transition temperatures, crystal field splittings and Debye temperatures have been derived.

scholarly journals Overview of Low-Temperature Heat Capacity Data for Zn2(C8H4O4)2.C6H12N2 and the Salam Hypothesis

Symmetry ◽  
2019 ◽  
Vol 11 (5) ◽  
pp. 657
Author(s):  
Svetlana Kozlova ◽  
Maxim Ryzhikov ◽  
Denis Pishchur ◽  
Irina Mirzaeva
Keyword(s):  
Phase Transition ◽  
Heat Capacity ◽  
Phase Transitions ◽  
Low Temperature ◽  
Metal Organic Framework ◽  
Model System ◽  
Temperature Heat ◽  
Metal Organic ◽  
Low Temperature Heat Capacity ◽  
Capacity Data

The review presents the progress in the analysis of low-temperature heat capacity of the metal-organic framework Zn2(C8H4O4)2.C6H12N2 (Zn-DMOF). In Zn-DMOF, left-twisted D3(S) and right-twisted D3(R) DABCO molecules (C6H12N2) can transform into each other by tunneling to form a racemate. Termination of tunneling leads to a phase transition in the subsystem of twisted molecules. It is suggested that Zn-DMOF may be considered a model system to study the mechanisms of phase transitions belonging to the same type as hypothetical Salam phase transitions.

13C solid-state MAS NMR studies of the low temperature phase transition in fullerene C60

2000 ◽  
Vol 2 (11) ◽  
pp. 2651-2654 ◽  
Author(s):  
Heyong He ◽  
Jose´ Teixeira Dias ◽  
John Foulkes ◽  
Jacek Klinowski
Keyword(s):  
Phase Transition ◽  
Solid State ◽  
Low Temperature ◽  
Fullerene C60 ◽  
Mas Nmr ◽  
Temperature Phase ◽  
Nmr Studies ◽  
Temperature Phase Transition ◽  
Low Temperature Phase

THORIUM-DOPING INDUCED HIGH-Tc SUPERCONDUCTIVITY IN Dy1-xThxFeAsO

2012 ◽  
Vol 26 (32) ◽  
pp. 1250207 ◽  
Author(s):  
YONGKANG LUO ◽  
XIAO LIN ◽  
YUKE LI ◽  
QIAN TAO ◽  
LINJUN LI ◽  
...  
Keyword(s):  
Phase Transition ◽  
Transition Temperature ◽  
Solid State ◽  
Low Temperature ◽  
Ambient Pressure ◽  
Magnetic Moments ◽  
Structural Phase ◽  
Parent Compound ◽  
Partial Substitution ◽  
High Tc

Parent compound of DyFeAsO was successfully synthesized by solid-state reaction under ambient pressure and superconductivity was induced by partial substitution of trivalent Dy 3+ ions with tetravalent Th 4+ in Dy 1-x Th x FeAsO . In the undoped parent compound, an anomaly in the resistivity appears around 140 K which corresponds to the structural phase transition and/or antiferromagnetic (AFM) order of the magnetic moments of Fe 2+ ions. At low temperature, another AFM order associated with the magnetic moments of Dy 3+ ions occurs at TN of 9.55 K. The AFM order around 140 K has significant influence on the transport properties, which can be interpreted by opening of partial gap on Fermi surface. Th doping suppresses the AFM order related to the Fe 2+ ions and the midpoint transition temperature [Formula: see text] of 49.3 K is observed for x = 0.3. Our results also indicate that the [ Ln 2 O 2]2+ layer has influence on the magnetism of [ Fe 2 As 2]2- layer.

In Search of the Molecular Triplet of C60 using Low Temperature Raman Spectroscopy.

2001 ◽  
Vol 675 ◽  
Author(s):  
G. Chambers ◽  
A.B. Dalton ◽  
H.J. Byrne
Keyword(s):  
Thin Films ◽  
Phase Transition ◽  
Raman Spectroscopy ◽  
Excited State ◽  
Solid State ◽  
Low Temperature ◽  
Excited States ◽  
Laser Intensity ◽  
Excitation Intensity ◽  
Raman Frequency

ABSTRACTThe excited state properties of C60 thin films have been probed in the temperature range 77–273K using Raman spectroscopy. The change in the Raman, 2Ag mode of C60 (whose position is largely independent of temperature) was monitored as a function of the excitation intensity at 514.5nm. This mode normally positioned at 1469cm-1, was seen to shift reversibly to a lower Raman frequency with increasing laser intensity. Two excited state species have been identified. The first, at 1466cm-1 has been associated with the molecular triplet of C60. The second species at 1463cm-1, has been speculated to be an excited state co-operative involving two or more excited states in the solid and is seen to be intrinsic to solid state C60 below the phase transition.

Unusual Structures, Phase Behavior, and Fluorescent Properties of 3-phenyl-1-(pyridin-2-yl)-1H-pyrazol-5-amine and Its’ ZnCl2 Complex

2019 ◽  
Author(s):  
Lana K. Hiscock ◽  
Delara Joekar ◽  
Zachary W. Schroeder ◽  
Victoria Jarvis ◽  
Kenneth E. Maly ◽  
...  
Keyword(s):  
Phase Transition ◽  
Solid State ◽  
Single Crystal ◽  
Fluorescence Enhancement ◽  
Fluid Phase ◽  
Fluorescent Properties ◽  
Single Crystal Structures ◽  
Crystal Phase Transition ◽  
Crystalline Domains ◽  
Melting And Solidification

The synthesis and single crystal structures of 3-phenyl-1-(pyridin-2-yl)-1<i>H</i>-pyrazol-5-amine (<b>L1</b>) and its complex with ZnCl<sub>2 </sub>are reported. <b>L1</b> exhibits supercooling, with a difference in melting and solidification points of over 100 <sup>o</sup>C. The complex [<b>L1</b>ZnCl<sub>2</sub>] has a room-to-low temperature single crystal-to-crystal phase transition in the solid state, while a birefringent fluid phase mixed with crystalline domains is observed at high temperatures. Significant fluorescence enhancement is observed upon formation of the ZnCl<sub>2</sub> complex.

A low temperature reversible phase transition for 1,1'-bis-(ferrocenyldimethylsilyl)ferrocenylene, (η5-FcSiMe2C5H4)2Fe, an oligomeric model for silyleneferrocenylene polymers

2000 ◽  
Vol 78 (11) ◽  
pp. 1511-1518 ◽  
Author(s):  
Mikhail Yu Antipin ◽  
Ivan I Vorontsov ◽  
Irene I Dubovik ◽  
Vladimir Papkov ◽  
Francisco Cervantes-Lee ◽  
...  
Keyword(s):  
Phase Transition ◽  
Solid State ◽  
Phase Space ◽  
Low Temperature ◽  
High Temperature Phase ◽  
Temperature Phase ◽  
X Ray Diffraction ◽  
Space Group ◽  
Reversible Phase Transition ◽  
Reversible Phase

We have reinvestigated the solid state structure of 1,1'-bis-(ferrocenyldimethylsilyl)ferrocenylene, (η5-FcSiMe2C5H4)2Fe, Fc = (η5-C5H5)Fe(η5-C5H4). Using a DSC technique we observed a reversible phase transition for this compound at 169(3)K with ΔH = 1.1 kJ/mol, and ΔS = 6.54 J/mol K. A single crystal X-ray diffraction study has demonstrated that this phase change involves a transformation from a high temperature phase, space group P21/c, Z = 2, to a triclinic low temperature phase, space group P[Formula: see text], Z = 4. The phase transition involves the loss of the molecular crystallographic center of symmetry and rotations about the terminal and central cyclopentadienyl ring pairs. The results are compared to those reported for ferrocene.Key words: solid state, phase transition, silyleneferrocenylene.

TEM of Phase Transitions in Tridymite and Cristobalite Based Materials.

2000 ◽  
Vol 6 (S2) ◽  
pp. 358-359
Author(s):  
Gustaaf Van Tendeloo
Keyword(s):  
Phase Transition ◽  
Phase Transitions ◽  
High Temperature ◽  
Solid State ◽  
Wide Temperature Range ◽  
Room Temperature ◽  
Paraelectric Phase ◽  
High Temperature Phase ◽  
Temperature Phase ◽  
Extended Defects

We have determined the structure of the paraelectric phase of BaAl2O4, which is a stuffed tridymite, by different TEM techniques and we will describe the phase transition between the ferroelectric room temperature phase and the paraelectric high temperature phase. We have also obtained HREM images of the higly radiation sensitive acristobalite phase of (Si0,9 Ge0,1)O2 and analysed the extended defects in this material.The stuffed tridymite BaAl2O4 is ferroelectric at room temperature and undergoes a paraelectric-ferroelectric (PEFE) phase transition. The transition is reversible, takes place over a wide temperature range (400K-670K) and has a dynamical character. BaAl2O4 is easily obtained by solid state reaction of BaCO3, and A12O4,. The stoichiometric amounts of the initial reagents were mixed, grinded in an agate mortar under acetone and pressed into a pellet. The pellet was annealed in alumina crucibles at 1000 °C and 1300 °C for 40 h in air and furnace cooled.

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