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

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

Ionic Dynamics in Plastic Crystal KNO2 Studied by 39K and 15N NMR

1994 ◽  
Vol 49 (1-2) ◽  
pp. 247-252 ◽  
Author(s):  
Motoko Kenmotsu ◽  
Hisashi Honda ◽  
Hiroshi Ohki ◽  
Ryuichi Ikeda ◽  
Tomoki Erata ◽  
...  
Keyword(s):  
Intermediate Phase ◽  
Relaxation Times ◽  
Nmr Relaxation ◽  
Lattice Relaxation ◽  
Lattice Relaxation Time ◽  
Spin Lattice Relaxation ◽  
15N Nmr ◽  
Temperature Phase ◽  
Self Diffusion ◽  
Spin Lattice

AbstractThe spin-lattice relaxation time of 39K NMR observed in the low-temperature phase (T<264.1 K) of KNO2 is explained by the quadrupole mechanism contributed from a newly found NO2- motion. The in-plane C3 reorientation and the overvall NO2 rotation as well as the self-diffusion were shown in the intermediate phase (T ≤ 314.7 K) and the high-temperature plastic phase (T < melting point: 710 K), respectively, by observing 39K and 15N NMR relaxation times and 15N lineshapes.

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.

Thallium Nuclear Magnetic Relaxation in Solid Thallium (I) Thiocyanate TlSCN: Phase Transition and Ionic Motion

1990 ◽  
Vol 45 (9-10) ◽  
pp. 1211-1216 ◽  
Author(s):  
Yoshihiro Furukawa ◽  
Daiyu Nakamura
Keyword(s):  
Phase Transition ◽  
Orthorhombic Phase ◽  
Lattice Relaxation ◽  
Lattice Relaxation Time ◽  
Spin Lattice Relaxation ◽  
Scalar Coupling ◽  
Temperature Phase ◽  
Self Diffusion ◽  
Spin Lattice ◽  
Low Temperature Phase

Abstract The NMR spin-lattice relaxation time (T1) and linewidth parameter (T2*) of 203Tl and 205T1 in solid T1SCN were measured from 290 K up to the melting point (Tm = 507 K). The nonexponential magnetization recovery of could be characterized by a short (T1s) and a long (T11) component. T11 showed a T-2 dependence below ca. 350 K in the orthorhombic phase (T<Tc = 371 K) and a minimum in the tetragonal phase (Tc<T<Tm), which were interpreted in terms of lattice vibrations and head-to-tail flips of the linear SCN- ions, respectively. A broad minimum of 77 around 360 K was explained in terms of indirect nucleus-electron scalar coupling between 203Tl and 205Tl, modulated via the anionic flips occurring in the symmetric and asymmetric potential fields for the highland low-temperature phase, respectively. The phase transition is closely related to dynamical disorder of the anionic orientations. At higher temperatures, translational self-diffusion of Tl+ was evidenced by the T2* and T1s results

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.

1H NMR Studieson the Molecular Dynamics of Acetylferrocene in Crystals

1988 ◽  
Vol 43 (1) ◽  
pp. 78-80 ◽  
Author(s):  
Atsushi Kubo ◽  
Ryuichi Ikeda ◽  
Daiyu Nakamura
Keyword(s):  
Phase Transition ◽  
Activation Energy ◽  
Relaxation Times ◽  
Lattice Relaxation ◽  
Lattice Relaxation Time ◽  
Spin Lattice Relaxation ◽  
Scanning Calorimetry ◽  
Two Phase ◽  
Spin Lattice ◽  
Packed Structure

Abstract The temperature dependence of 1H spin-lattice relaxation time was determined at 20 MHz for solid acetylferrocene [(C5H5) (C5H4COCH3)Fe] from ca. 80 K up to the m.p. (359 K). Rather large activation energies of 21 and 24 kJ mol-1 for the C5 reorientations of the two crystallographically nonequivalent non-substituted cyclopentadienyl rings were obtained, indicating that the crystal has a closely packed structure. The two kinds of CH3 groups attached to the substituted cyclopenta­dienyl rings were assumed to be approximately equivalent and gave a low activation energy of 4 kJ mol-1 for the C3 reorientation. No phase transition was observed in the relaxation times or in additional experiments of differential thermal analysis although the presence of two phase transi­tions has been reported previously at temperatures immediately below the melting temperature by means of differential scanning calorimetry.

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.

Incommensurability and Domain Structure of K2SbF5

2002 ◽  
Vol 57 (6-7) ◽  
pp. 456-460
Author(s):  
A. M. Panich ◽  
L. A. Zemnukhova ◽  
R. L. Davidovich
Keyword(s):  
Relaxation Time ◽  
Phase Transitions ◽  
Lattice Relaxation ◽  
Lattice Relaxation Time ◽  
Spin Lattice Relaxation ◽  
Temperature Phase ◽  
X Ray Diffraction ◽  
Spin Lattice ◽  
Relaxation Measurements ◽  
Increasing Temperature

Phase transitions and incommensurability in K2SbF5 have been studied by means of 123Sb NQR spectra and spin-lattice relaxation measurements. The phase transitions occur at 117, 135 and 260 K. The line shape and temperature dependence of the spin-lattice relaxation time T1 at 135 to 260 K are characteristic for an incommensurate state with a plane wave modulation regime. At 117 to 135 K a distinct fine structure of the NQR spectra has been observed. The X-ray diffraction pattern of this phase is interpreted as a coexistence of two modulation waves along the a and b axis with wave vectors (a*/6 + b*/6) and (a*/2 + b*/2), respectively. The best interpretation that fits our NQR data is a coexistence of two domains, the structures of which are modulated with different periods in such a manner that each domain exhibits only one of the aforementioned modulation waves. Redistribution of line intensities with the variation of temperature shows that one of the domains becomes energetically preferable on cooling and is transformed into the low temperature phase at 117 K. The 123SbNQR measurements in K2SbF5 show unusually short values of T1, which become close to the spin-spin relaxation time T2 with increasing temperature. - Pacs: 61.44.Fw, 64.60, 64.70, 64.70.Rh, 76.60

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.

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