Structural Phase Transitions and Ionic Motions in Pyridinium Hexachlorotellurate(IV),Hexachlorostannate(IV), and Hexabromostannate(IV) Crystals as Studied by 1H NMR

1989 ◽  
Vol 44 (4) ◽  
pp. 300-306 ◽  
Author(s):  
Yutaka Tai ◽  
Tetsuo Asaji ◽  
Ryuichi Ikeda ◽  
Daiyu Nakamura
Keyword(s):  
Phase Transitions ◽  
High Temperature ◽  
Structural Phase ◽  
Lattice Relaxation ◽  
Relaxation Mechanism ◽  
Lattice Relaxation Time ◽  
Spin Lattice Relaxation ◽  
Scanning Calorimetry ◽  
Spin Lattice ◽  
H Nmr

Abstract The 1H NMR second moment M2 and the spin-lattice relaxation time T1 are determined for pyridinium hexachlorotellurate(IV), hexachlorostannate(IV), and hexabromostannate(IV) at various temperatures above ca. 140 K. The phase transition temperatures already reported from halogen NQR experiments are determined as 272, 331, and 285 K, respectively, by differential thermal analysis (DTA). The DTA as well as differential scanning calorimetry measurements show that the above phase transitions are of second-order. For pyridinium hexachlorotellurate(IV) and hexa-bromostannate(I V), a sharp 1H T1 dip was observed at the transition temperature. This is interpreted in terms of a phenomenon related to the critical fluctuation of an order parameter. From the measurements of 1H M2, 60° two-site jumps (60° flips) around the pseudo C6 axis of the cation are suggested to occur in the high temperature phases of the complexes. Modulation of X...1H (X = CI, Br) magnetic dipolar interactions due to the reorientational motion of the complex anions is considered as a possible relaxation mechanism in the high temperature phases.

Motions of Methylammonium Ions in (CH3NH3)2ZnBr4 Crystals Studied by 1H NMR and Thermal Measurements

1990 ◽  
Vol 45 (7) ◽  
pp. 923-927
Author(s):  
Hiroyuki Ishida ◽  
Kentaro Takagi ◽  
Tadashi Iwachido
Keyword(s):  
Solid Phase ◽  
Lattice Relaxation ◽  
Lattice Relaxation Time ◽  
High Temperature Phase ◽  
Spin Lattice Relaxation ◽  
Temperature Phase ◽  
Scanning Calorimetry ◽  
Self Diffusion ◽  
Spin Lattice ◽  
H Nmr

AbstractMeasurements of the 1H spin-lattice relaxation time T1, the linewidth parameter T*2the second moment of 1H NMR absorption, differential thermal analysis, and differential scanning calorimetry were performed on methylammonium tetrabromozincate(II) crystals from 58 to above 500 K. A solid-solid phase transition was located at 456 K. In the room temperature phase, 120° reorientational jumps of CH3 and NH3+ groups in the cation about its C -N bond axis were detected. In the high-temperature phase, the cations undergo overall reorientation as well as translational self-diffusion. The activation energy for the cationic self-diffusion was evaluated to be 18 kJ mol-1 .

A Highly Disordered New Solid Phase Containing Isotropically Reorienting Cations in (CH3NH3 )2CdBr4 Studied by 1H NMR and Thermal Measurements

1990 ◽  
Vol 45 (9-10) ◽  
pp. 1190-1192 ◽  
Author(s):  
Hiroyuki Ishida ◽  
Kentaro Takagi ◽  
Mifune Terashima ◽  
Daiyu Nakamura
Keyword(s):  
Room Temperature ◽  
Solid Phase ◽  
Lattice Relaxation ◽  
Lattice Relaxation Time ◽  
Spin Lattice Relaxation ◽  
Temperature Phase ◽  
Scanning Calorimetry ◽  
Spin Lattice ◽  
H Nmr ◽  
Thermal Measurements

Abstract The 1H spin-lattice relaxation time, linewidth, second moment of 1H NMR absorption, differen-tial thermal analysis, and differential scanning calorimetry of methylammonium tetrabromocado-mate(II) crystals were studied. A new solid phase was found between 482 K and the melting point (493 K). The 1H NMR measurements revealed the presence of overall reorientation of methyl-ammonium cations in this phase. In the room temperature phase, 120° reorientational jumps of the CH3 and NH3+ groups were detected.

Successive Phase Transitions in Potassium Hexachloroselenate(IV) Revealed by 35Cl NQR

1996 ◽  
Vol 51 (5-6) ◽  
pp. 705-709 ◽  
Author(s):  
Tetsuo Asaji ◽  
Masaki Ohkawa ◽  
Takehiko Chiba ◽  
Makoto Kaga
Keyword(s):  
Phase Transitions ◽  
Temperature Dependence ◽  
Structural Phase ◽  
Lattice Relaxation ◽  
Lattice Relaxation Time ◽  
Spin Lattice Relaxation ◽  
Structural Phase Transitions ◽  
Spin Lattice ◽  
35Cl Nqr ◽  
Successive Phase

Abstract K2SeCl6 undergoes structural phase transitions of first order at 35 K, 65 K, and 79 K. The temperature dependence of the 35Cl NQR spin-lattice relaxation time suggests that the phase transitions at 65 K and 79 K are displacive ones associated with a resonant soft mode. The presence of a precursor cluster is suggested by the temperature dependence of the signal intensity above 79 K.

A nuclear magnetic resonance investigation of solid tetraphosphorus trisulphide

1978 ◽  
Vol 364 (1719) ◽  
pp. 553-567 ◽  
Keyword(s):  
Phase 1 ◽  
Lattice Relaxation ◽  
Relaxation Mechanism ◽  
Lattice Relaxation Time ◽  
Spin Lattice Relaxation ◽  
Minor Role ◽  
High Resolution Spectrum ◽  
Basal Nuclei ◽  
Spin Lattice ◽  
A Minor

The 31 P n. m. r. spectrum and spin–lattice relaxation time in polycrystalline P 4 S 3 have been measured between 77 and 500 K in the range 7 to 25 MHz. In phase II the 31 P n. m. r. spectra and second moments are dominated by the anisotropic chemical shift interactions. Close to the first-order phase transition at 314 K the spectra are narrowed by reorientation of the molecules about their triad axes. This motion also generates anisotropicshift spin-lattice relaxation notable for its absence of frequency dependence. The activation energy of this motion was found to be 34 kJ mol -1 . Nuclear dipolar interactions play only a minor role. In phase 1 the molecules exhibit rapid quasi-isotropic reorientation and diffusion. The anisotropic broadening interactions are averaged out and an AB 3 high-resolution spectrum of a doublet and quartet are resolved at 420 K, well below the melting point, 446 K. In this phase the spin–rotation interaction relaxation mechanism becomes dominant. Taking advantage of the remarkable motional narrowing in this compound we report the first solid-state n. m. r. J spectrum. This spectrum, recorded at 410 K, allowed the J coupling between apical and basal nuclei in solid P 4 S 3 to be measured accurately, 70.4 ± 0.5 Hz.

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.

1HNMR Study on the Motion of NH4+ in Ferroelectric NH4H(ClH2CCOO)2 and Mixed (NH4)1-xRbxH(ClH2CCOO)2 (x = 0.15)

2002 ◽  
Vol 57 (11) ◽  
pp. 883-887 ◽  
Author(s):  
M. Zdanowska-Fra̡czek ◽  
A. Kozaka ◽  
R. Jakubasb ◽  
J. Wa̡sickia ◽  
R. Utrechta
Keyword(s):  
Relaxation Time ◽  
Group Dynamics ◽  
Nmr Relaxation ◽  
Activation Parameters ◽  
Lattice Relaxation ◽  
Relaxation Mechanism ◽  
Lattice Relaxation Time ◽  
Spin Lattice Relaxation ◽  
Temperature Dependent ◽  
Spin Lattice

Temperature-dependent proton NMR relaxation time measurements have been performed at 60 MHz in order to study the NH4+ dynamics in ferroelectric NH4H(ClH2CCOO)2 and mixed Rbx(NH4)1-x(ClH2CCOO)2, where x = 0.15. The data indicate that the dominant relaxation mechanism for the NMR spin-lattice relaxation time T 1 in both crystals involves simultaneous NH4 group reorientation about their C2 and C3 symmetry axis in the paraelectric phase. Details of the NH4+reorientation have been inferred from analysis of temperature dependence of T1 assuming the Watton model. The activation parameters of the motionshave been determined.It has been found that the substitution of Rb does not change the activation parameters of the NH4 group dynamics.

Chlorine Nuclear Quadrupole Relaxation due to the Motion of Pyridinium Cations in Pyridinium Hexachlorometallates(IV): (pyH)2 MCl6 (M = Sn, Pb, Te)

1990 ◽  
Vol 45 (3-4) ◽  
pp. 477-480 ◽  
Author(s):  
Yutaka Tai ◽  
Tetsuo Asaji ◽  
Daiyu Nakamura
Keyword(s):  
Lattice Relaxation ◽  
Relaxation Mechanism ◽  
Lattice Relaxation Time ◽  
Spin Lattice Relaxation ◽  
Reorientational Motion ◽  
Quadrupole Relaxation ◽  
Potential Wells ◽  
Spin Lattice ◽  
Pyridinium Cations ◽  
Nuclear Quadrupole Relaxation

Abstract The temperature dependence of the chlorine quadrupole spin-lattice relaxation time T1Q was observed for one of the three 35Cl NQR lines of (pyH)2 MCl6(M = Sn, Pb, Te). Each T1Q curve can be devided into three temperature regions. In the low-and high-temperature regions, T1Q is dominantly determined by the relaxation mechanism due to the libration and reorientation of [MCl6]2- , respectively. In the intermediate temperature region, T1Q results from the modulation of the electric field gradient by the motion of the neighboring pyridinium cations. This way the reorientational motion of the cation between potential wells with nonequivalent depths is precisely characterized.

Proton Magnetic Resonance and Molecular Motion in Solid Methyl-Piperidines and Piperazines

1977 ◽  
Vol 32 (8) ◽  
pp. 882-885 ◽  
Author(s):  
R. Schüler ◽  
L. Brücher ◽  
W. Müller-Warmuth
Keyword(s):  
Proton Magnetic Resonance ◽  
Molecular Motion ◽  
Lattice Relaxation ◽  
Lattice Relaxation Time ◽  
Spin Lattice Relaxation ◽  
Methyl Group ◽  
Spin Lattice ◽  
H Nmr ◽  
Second Moments ◽  
Line Narrowing

Abstract The 1H-NMR spin-lattice relaxation time and lineshape in solid 2-, 3-, and 4-methyl-piperidine, in 2-and N-methyl-piperazine, and in NN′-diinethyl-piperazine has been measured from low temperatures to the melting point. For all cases, the experimental data can be described by classical rotation of the methyl group. Activation energies governing this motion are between 9 and 14 kJ/mole. Second moments are reduced from about 25 G2 to 17 G2. No further line-narrowing was observed.

Spin–lattice relaxation of 1,2-dichloroethane in different solvents

1969 ◽  
Vol 47 (24) ◽  
pp. 4635-4638 ◽  
Author(s):  
E. Bock ◽  
E. Tomchuk
Keyword(s):  
Relaxation Rate ◽  
Lattice Relaxation ◽  
Relaxation Mechanism ◽  
Lattice Relaxation Time ◽  
Spin Lattice Relaxation ◽  
Spin Lattice ◽  
Weakly Magnetic ◽  
Solvent Molecules ◽  
The Individual ◽  
Deuterated Benzene

The spin–lattice relaxation time of the 1,2-dichloroethane molecule has been determined in 6 different nonmagnetic or weakly magnetic solvents at 20 °C, viz: deuterated benzene, carbon disulfide, deuterated 1,2-dichloroethane, carbon tetrachloride, and deuterated chloroform. From the experimental results the relaxation rate in infinitely dilute solution, the so called intramolecular relaxation rate, was determined for each solvent. It was found that the observed intramolecular relaxation rate could be successfully interpreted as arising solely from a dipole–dipole relaxation mechanism. It was further found that the individual differences in the value of the intramolecular spin–lattice relaxation rate of the 1,2-dichloroethane molecule in different solvents could be accounted for in terms of weak complex formation between the solute and solvent molecules.

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