NMR Study of Cation Motions in Ferroic [C(NH2)3]3Bi2Br9

2000 ◽  
Vol 55 (6-7) ◽  
pp. 570-574 ◽  
Author(s):  
M. Grottel ◽  
Z. Paja̡ka ◽  
R. Jakubasb
Keyword(s):  
Relaxation Time ◽  
Phase Transitions ◽  
Wide Temperature Range ◽  
Proton Nmr ◽  
Lattice Relaxation ◽  
Lattice Relaxation Time ◽  
Spin Lattice Relaxation ◽  
Potential Barriers ◽  
Spin Lattice ◽  
Nmr Study

The proton NMR second moment and spin-lattice relaxation time of polycrystalline [C(NH2)3]3Bi2Br9 were studied in a wide-temperature range. Dynamical inequivalence of two crystallographically different guanidinium cations has been revealed . The C3 reorientation of the two types of cations was found to be hindered by different potential barriers (25.1 kJ/mol and 34.7 kJ/mol). At higher temperatures an overall reorientation of the cations was revealed. The existence and order-disorder character of the phase transitions at 333, 350, 415, and 425 K have been confirmed.

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

Proton NMR Study of Molecular Dynamics in Hydrazinium Perchlorate

1990 ◽  
Vol 45 (2) ◽  
pp. 102-106
Author(s):  
K. Ganesan ◽  
R. Damle ◽  
J. Ramakrishna
Keyword(s):  
Molecular Dynamics ◽  
Relaxation Time ◽  
Lattice Relaxation ◽  
Lattice Relaxation Time ◽  
Proton Spin ◽  
Spin Lattice Relaxation ◽  
Temperature Minimum ◽  
Second Moment ◽  
Spin Lattice ◽  
Nmr Study

AbstractThe proton spin-lattice relaxation time T1 (at 5.4, 10 and 15 MHz) and second moment M2 (at 9.8 MHz) have been measured in hydrazinium Perchlorate (N2H5ClO4). The temperature dependence of T, shows two minima. The low temperature T, minimum has been explained in terms of NH3 reorientation about the N-N axis while the high temperature minimum is attributed to the exchange of protons within the NH2 group (180° flip about the H - N - H bisectrix). The activation energies for NH3 and NH: motions are found to be 20.5 kJ mol-1 and 39.8 kJ mol-1 , respectively. The second moment variation with temperature shows two transitions around 120 K and 210 K and has been discussed in terms of NH3/NH2 motions.

1H and 19F NMR Study of Ammonium Ion Motion in Ammonium Trifluorostannate (II)

1988 ◽  
Vol 43 (2) ◽  
pp. 187-188
Author(s):  
Kiyofumi Hirokawa ◽  
Yoshihiro Furukawa
Keyword(s):  
Activation Energy ◽  
Relaxation Time ◽  
Lattice Relaxation ◽  
Lattice Relaxation Time ◽  
Spin Lattice Relaxation ◽  
Ammonium Ion ◽  
Ion Motion ◽  
Spin Lattice ◽  
Nmr Study ◽  
Temperature Dependences

Abstract The temperature dependences of the second moment and spin-lattice relaxation time of 1H and 19F NMR were measured on ammonium trifluorostannate (II) NH4SnF3. It was found that the NH4+ ions having a C3 symmetry in the crystal undergo overall reorientations with an activation energy of 22 kJ mol - 1.

An 1H NMR Study on the Cationic Motion in Solid tert-Butylammonium Chloride and Bromide

1991 ◽  
Vol 46 (3) ◽  
pp. 265-268 ◽  
Author(s):  
Hiroyuki Ishida ◽  
Syuichi Inada ◽  
Naomi Hayama ◽  
Daiyu Nakamura ◽  
Ryuichi Ikeda
Keyword(s):  
Relaxation Time ◽  
1H Nmr ◽  
Room Temperature ◽  
Lattice Relaxation ◽  
Lattice Relaxation Time ◽  
Spin Lattice Relaxation ◽  
X Ray ◽  
Spin Lattice ◽  
H Nmr ◽  
Nmr Study

AbstractThe 1H spin-lattice relaxation time (T1) in solid (CD3)3CNH3Cl and (CD3)3CNH3Br was measured above room temperature and the motional parameters for the reorientation of the NH3+ groups were determined. The 1H NMR absorptions measured in the same temperature range for (CH3)3CNH3Cl and (CH3)3CNH3Br indicate the presence of superimposed several cationic motions commonly taking place in both compounds. From X-ray powder patterns taken at room temperature, the bromide was found to be isomorphous with the chloride

Low Temperature Isotope Effect in Ammonium Hexachloroselenate(IV) Studied by 35Cl NQR

1994 ◽  
Vol 49 (1-2) ◽  
pp. 297-301 ◽  
Author(s):  
Y. Kume ◽  
T. Asaji ◽  
R. Ikeda
Keyword(s):  
Relaxation Time ◽  
Phase Transitions ◽  
Low Temperature ◽  
Transition Point ◽  
Lattice Relaxation ◽  
Lattice Relaxation Time ◽  
Spin Lattice Relaxation ◽  
Spin Lattice ◽  
Soft Modes ◽  
35Cl Nqr

Abstract The temperature dependence o f the 35Cl NQR frequency and spin-lattice relaxation time T1Q of (NH4)2SeCl6 and (ND4)2SeCl6 were measured from 400 K to 24.8 and 53.8 K, respectively. The disappearance of NQR signals in the low temperature region of both salts is attributed to phase transitions. We concluded from the temperature behavior of just above the transition point that the operative mechanism o f the transition is different in these salts: The transition of (ND4)2SeCl6 seems to be associated with rotary soft modes, while in the natural salt non-rotary soft modes seem to play an important role at the transition.

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