Chlorine-35 NQR Study of a Structural Phase Transition in (ND4)2PdCl6

1998 ◽  
Vol 53 (6-7) ◽  
pp. 514-517 ◽  
Author(s):  
Yoshio Kume ◽  
Tetsuo Asaji
Keyword(s):  
Phase Transition ◽  
Structural Phase ◽  
Relaxation Times ◽  
Lattice Relaxation ◽  
Spin Lattice Relaxation ◽  
Temperature Phase ◽  
Spin Lattice ◽  
First Order Phase Transition ◽  
Temperature Dependences ◽  
First Order Phase

Abstract Temperature dependences of 35Cl NQR frequencies and spin-lattice relaxation times were measured at 4.2 to 400 K for natural and deuterated ammonium hexachloropalladate. It was confirmed that only the deuterated salt undergoes a first order phase transition at 30 K. The crystal structure of the low-temperature phase is predicted to be the same as that of the deuterated ammonium hexachloroplatinate and hexachloroplumbate. The mechanism of the deuteration-induced phase transition is discussed.

Temperature Dependences of NQR Frequencies and Nuclear Quadrupole Relaxation Times of Chlorine in 2,6-Lutidinium Hexachlorotellurate (IV) as Studied by Pulsed NQR Techniques

1990 ◽  
Vol 45 (3-4) ◽  
pp. 485-489
Author(s):  
Keizo Horiuchi ◽  
Takashige Shimizu ◽  
Hitomi Iwafune ◽  
Tetsuo Asaji ◽  
Daiyu Nakamura
Keyword(s):  
Phase Transition ◽  
Relaxation Times ◽  
Lattice Relaxation ◽  
Spin Lattice Relaxation ◽  
Temperature Phase ◽  
Quadrupole Relaxation ◽  
Spin Lattice ◽  
Resonance Frequencies ◽  
Temperature Dependences ◽  
Nuclear Quadrupole

Abstract The temperature dependences of the 35Cl NQR frequencies vQ and the nuclear quadrupole spin-lattice relaxation times T1Q in 2,6-lutidinium hexachlorotellurate (IV) was observed at various temperatures between 80 and 343 K. This crystal undergoes a phase transition at Tc = 229 K. A single and three pairs of 35Cl NQR frequencies were observed above and below Tc , respectively. The hysteresis of the phase transition and a discontinuity in the temperature dependence of the resonance frequencies at Tc indicate that this phase transition is of first order. Although the resonance frequencies of the pairs in the low temperature phase are very close to one another, T1Q and below Tc could be accurately determined by measuring the Fourier transform spectra of each line. Above ca. 250 K, T1Q showed an exponential decrease which is attributable to the overall reorientational motion of [TeCl6]2- with an activation energy of 82 kJ mol-1

scholarly journals 35Cl NQR Relaxation of the Molecular Ferroelectric 5,6-Dichloro-2-Methylbenzimidazole with Hydrogen-Bonded Molecular Chain

Crystals ◽  
2020 ◽  
Vol 10 (2) ◽  
pp. 56
Author(s):  
Tetsuo Asaji
Keyword(s):  
Relaxation Times ◽  
Lattice Relaxation ◽  
Relaxation Mechanism ◽  
High Temperature Phase ◽  
Spin Lattice Relaxation ◽  
Temperature Phase ◽  
Spin Lattice ◽  
First Order Phase Transition ◽  
Significant Difference ◽  
First Order Phase

The 35Cl nuclear quadruple resonance (NQR) frequencies and spin-lattice relaxation times were measured in the temperature range of 4.2–420 K, of the above-room-temperature ferroelectric 5,6-dichloro-2-methylbenzimidazole, the ferroelectricity of which is thought to arise from the positional ordering of protons along chain of N-H...N hydrogen bonds. The first-order phase transition was clearly detected at around 400 K, as a discontinuity in the temperature dependence of NQR frequencies. The two NQR lines observed showed a much more significant difference in frequency in the high-temperature phase. This is consistent with the recently reported symmetry-lowering of crystal structure on warming. The relaxation mechanism in the low-temperature phase is discussed.

Cation and Anion Reorientation at Phase Transition in Pyridinium Tetrafluoroborate

1990 ◽  
Vol 45 (1) ◽  
pp. 33-36 ◽  
Author(s):  
J. Wąsicki ◽  
Z. Pająk ◽  
A. Kozak
Keyword(s):  
Phase Transition ◽  
Relaxation Times ◽  
Activation Parameters ◽  
Lattice Relaxation ◽  
High Temperature Phase ◽  
Spin Lattice Relaxation ◽  
Temperature Phase ◽  
Spin Lattice ◽  
Relaxation Effects ◽  
Temperature Dependences

AbstractTemperature dependences of 1H and 19F second moment and spin-lattice relaxation times for polycrystalline pyridinium tetrafluoroborate were measured. A phase transition was discovered at 202 K. A model of cation reorientation between inequivalent (low-temperature phase) and equivalent (high-temperature phase) equilibrium positions is proposed. Whether the anion reorients isotropically or about a symmetry axis cannot be decided. An analysis of cross-relaxation effects yielded activation parameters for cation and anion reorientation. The rotational correlation times for both ions converge just at the phase transition reaching the value of 10-10s.

Dynamic Properties and Phase Transitions in A2ZnBr4(A= (CH3)4 N and (CH3)4P) as Studied by 79Br NQR and Multinuclear NMR

1998 ◽  
Vol 53 (6-7) ◽  
pp. 459-465 ◽  
Author(s):  
Hironobu Tada ◽  
Hirokazu Nakayama ◽  
Nobuo Nakamura
Keyword(s):  
Phase Transition ◽  
Phase Transitions ◽  
Dynamic Properties ◽  
Relaxation Times ◽  
Lattice Relaxation ◽  
Spin Lattice Relaxation ◽  
Transition Temperatures ◽  
Spin Lattice ◽  
Temperature Dependences ◽  
79Br Nqr

Abstract In order to understand the mechanism of ferroelastic phase transitions in A2ZnBr4 (A = (CH3)4 N and (CH3)4 P), the temperature dependences of 79Br NQR frequencies and the spin-lattice relaxation times were measured. The temperature dependences of the 1H and 31P spin-lattice relaxation times were measured as well for a possible correlation between the cation dynamics and the phase transition. Although the phase transition temperatures of these two compounds differ much (~ 100 K), the correlation times for the cation reorientation at the individual transition temperatures amount to some 10-11 s for both compounds.

133Cs NMR Spin-Lattice Relaxation Time and Chemical Shift Studies on Cs2MX4 Crystals with Sr2GeS4 and β-K2SO4 Structures Performing no Low Temperature Phase Transition

2002 ◽  
Vol 57 (6-7) ◽  
pp. 461-464 ◽  
Author(s):  
Koh-ichi Suzuki ◽  
Shin’ichi Ishimaru ◽  
Ryuichi Ikeda
Keyword(s):  
Phase Transition ◽  
Relaxation Times ◽  
Lattice Relaxation ◽  
Type Systems ◽  
Lattice Relaxation Time ◽  
Spin Lattice Relaxation ◽  
Temperature Phase ◽  
Central Lines ◽  
Spin Lattice ◽  
The Difference

133Cs NMR spectra and spin-lattice relaxation times T1 in crystalline Cs2ZnCl4 and Cs2ZnBr4 with -K2SO4 structure, and Cs2CdI4 and Cs2HgI4 with Sr2GeS4 structure, which have no phase transition in the lower temperature regions, weremeasured to clarify the relation between the interionic covalency and crystal structures. Two central lines corresponding to two crystallographically inequivalent Cs sites were observed in all compounds. One of the two peaks in β-K2SO4-type compounds appears below 40 ppm, but another peak in those compounts and the both lines in Sr2GeS4-type compounds show larger shifts, 130 - 200 ppm. The temperature dependences of T1 observed in Sr2GeS4-type compounds were close to the theoretical behaviour, calculated by considering contributions from normal lattice vibrations. Deviations from the calculation obtained for β-K2SO4-type systems are attributable to the difference in interionic interactions, i. e., partial covalency, in the crystals

Parameterization of the coupling between strain and order parameter for LuF[SeO3]

2014 ◽  
Vol 47 (2) ◽  
pp. 701-711 ◽  
Author(s):  
Oxana V. Magdysyuk ◽  
Melanie Müller ◽  
Robert E. Dinnebier ◽  
Christian Lipp ◽  
Thomas Schleid
Keyword(s):  
Phase Transition ◽  
Order Parameter ◽  
Structural Phase ◽  
High Temperature Phase ◽  
Temperature Phase ◽  
Time Resolved ◽  
Synchrotron Powder Diffraction ◽  
First Order Phase Transition ◽  
Temperature Phase Transition ◽  
First Order Phase

The high-temperature phase transition of LuF[SeO3] has been characterized by time-resolved high-resolution synchrotron powder diffraction. On heating, a second-order structural phase transition was found at 393 K, while on cooling the same phase transition occurs at 371 K, showing a large hysteresis typical for a first-order phase transition. Detailed analysis using sequential and parametric whole powder pattern fitting revealed that the coupling between the strain and the displacive order parameter determines the behaviour of the material during the phase transition. Different possible coupling mechanisms have been evaluated and the most probable rationalized.

1H and 19F NMR Study of Cation and Anion Motions in Guanidinium Fluoroantimonates

1995 ◽  
Vol 50 (8) ◽  
pp. 742-748 ◽  
Author(s):  
M. Grottel ◽  
A. Kozak ◽  
Z. Pająk
Keyword(s):  
Solid Phase ◽  
Relaxation Times ◽  
Activation Parameters ◽  
Lattice Relaxation ◽  
Spin Lattice Relaxation ◽  
Temperature Phase ◽  
Fluorine Nmr ◽  
Spin Lattice ◽  
Nmr Study ◽  
Guanidinium Cation

Abstract Proton and fluorine NMR linewidths, second moments, and spin-lattice relaxation times of polycrystalline [C(NH2)3]2SbF5 and C(NH2)3SbF6 were studied in a wide temperature range. For the pentafluoroantimonate, C3-reorientation of the guanidinium cation and C4-reorientation of the SbF5 anion were revealed and their activation parameters determined. The dynamical inequivalence of the two guanidinium cations was evidenced. For the hexafluoroantimonate, two solid-solid phase transitions were found. In the low temperature phase the guanidinium cation undergoes C3 reorien­ tation while the SbF6 anion reorients isotropically. The respective activation parameters were derived. At high temperatures new ionic plastic phases were evidenced.

Phase transitions in solid cycloheptene

1990 ◽  
Vol 68 (4) ◽  
pp. 604-611 ◽  
Author(s):  
Julian Haines ◽  
D. F. R. Gilson
Keyword(s):  
Phase Transition ◽  
High Temperature ◽  
Low Temperature ◽  
Lattice Relaxation ◽  
Proton Spin ◽  
Spin Lattice Relaxation ◽  
Temperature Phase ◽  
Scanning Calorimetry ◽  
Spin Lattice ◽  
Low Temperature Phase

The phase transition behaviour of cycloheptene has been investigated by differential scanning calorimetry, proton spin-lattice relaxation, and vibrational spectroscopy (infrared and Raman). Two solid–solid phase transitions were observed, at 154 and 210 K, with transition enthalpies and entropies of 5.28 and 0.71 kJ mol−1 and 34.3 and 3.4 JK−1, respectively. Cycloheptene melted at 217 K with an entropy of melting of 4.5 JK−1 mol−1. The bands in the vibrational spectra of the two high temperature phases were broad and featureless, characteristic of highly disordered phases. The presence of other conformers, in addition to the chair form, was indicated from bands in the spectra. The ring inversion mode was highly phase dependent and exhibited soft mode type behaviour prior to the transition from the low temperature phase. The low frequency Raman spectra (external modes) of these phases indicated that the molecules are undergoing isotropic reorientation. In the low temperature phase, the vibrational bands were narrow; the splitting of the fundamentals into two components and the presence of nine external modes are consistent with unit cell symmetry of either C2 or Cs with two molecules per primitive unit cell. A glassy state can be produced from the intermediate phase and the vibrational spectra were very similar to those of the high temperature phases, indicating that static disorder was present. The barriers to reorientation, as obtained from proton spin-lattice relaxation measurements, are 9.0 kJ mol−1 in both the high temperature phases, and 15.4 kJ mol−1 in the low temperature, ordered phase. Keywords: cycloheptene, phase transition, differential scanning calorimetry, NMR, vibrational spectroscopy.

Deuterium NMR Study of the Solid-Solid Phase Transition in Phenethylammonium Bromide

1991 ◽  
Vol 46 (8) ◽  
pp. 691-696 ◽  
Author(s):  
Marco L. H. Gruwel ◽  
Roderick E. Wasylishen
Keyword(s):  
Phase Transition ◽  
Low Temperature ◽  
Line Shape ◽  
Lattice Relaxation ◽  
Spin Lattice Relaxation ◽  
Temperature Phase ◽  
Spin Lattice ◽  
H Nmr ◽  
Line Shapes ◽  
Low Temperature Phase

AbstractUsing 2H NMR, the dynamics of the cation in phenethylammonium bromide were studied in the two solid phases. Line shape and spin-lattice relaxation rate studies of the ammonium headgroups and the adajacent methylene groups indicate the onset of alkyl-chain motion prior to the first order phase transition. In the low-temperature phase the line shape and the spin-lattice relaxation rates of the -ND3 groups are consistent with C3 jumps and an activation energy of 54±4 kJ mol-1. However, in the high-temperature phase the spin-lattice relaxation studies indicate the presence of small-angle diffusion of the -ND3 groups around the C3 symmetry axis. In this phase the -CD2- groups show line shapes typical of large-amplitude two-site jumps occurring at a rate > 107 s-1 . In the low-temperature phase, at temperatures below 295 K, the -CD2- 2H NMR line shapes indicate that the C - D bonds are essentially static

Molecular Reorientation in the Plastic Crystalline Phase of Tris

1979 ◽  
Vol 32 (4) ◽  
pp. 905 ◽  
Author(s):  
RE Wasylishen ◽  
PF Barron ◽  
DM Doddrell
Keyword(s):  
Phase Transition ◽  
Relaxation Times ◽  
Lattice Relaxation ◽  
Spin Lattice Relaxation ◽  
X Ray Diffraction ◽  
Scanning Calorimetry ◽  
Molecular Reorientation ◽  
Liquid Phase Transition ◽  
X Ray ◽  
Spin Lattice

Carbon-13 N.M.R. spectra of tris(hydroxymethyl)aminomethane (Tris) have been measured between 407 and 461 K. Proton-decoupled 13C N.M.R. spectra of solid Tris between 407 K and its melting point are relatively sharp (v� < 30 Hz) indicating rapid overall molecular reorientation in this temperature range. It was not possible to detect a 13C N.M.R, signal for Tris below 407 K. The observed 13C N.M.R. spin-lattice relaxation times appear continuous across the solid ↔ liquid phase transition. From the temperature dependence of T1, a rotational activation energy of 51.6 � 6 kJ mol-1 is calculated, which indicates that the molecules must expend considerable energy in reorienting. The N.M.R. results are discussed in relation to previous differential scanning calorimetry and X-ray diffraction data which indicate that Tris undergoes a solid ↔ solid transition at 407 K.

Sign in / Sign up

Export Citation Format

Share Document