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.

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

35Cl NQR and Molecular Motion in Solid C6X5Cl (X = H, F)

1992 ◽  
Vol 47 (1-2) ◽  
pp. 330-332 ◽  
Author(s):  
A. D. Gordeev ◽  
G. B. Soifer ◽  
A. P. Zhukov
Keyword(s):  
Relaxation Time ◽  
Molecular Motion ◽  
Lattice Relaxation ◽  
Lattice Relaxation Time ◽  
Activation Energies ◽  
Spin Lattice Relaxation ◽  
Melting Points ◽  
Spin Lattice Relaxation Time ◽  
Spin Lattice ◽  
35Cl Nqr

AbstractThe 35Cl NQR frequency and spin-lattice relaxation time of solid chlorobenzene and chloropentafluorobenzene at temperatures from 77 K to the melting points have been measured and explained by thermoactivated librations and reorientations of the molecules around the normal to their plane. The activation energies of these motions have been estimated

Calculated Spin-lattice Relaxation of 103Ru Compared with Low Temperature Quadrupole Orientation Measurements

1994 ◽  
Vol 49 (1-2) ◽  
pp. 395-400 ◽  
Author(s):  
R. Markendorf
Keyword(s):  
Relaxation Time ◽  
Low Temperature ◽  
Reference Value ◽  
Lattice Relaxation ◽  
Lattice Relaxation Time ◽  
Spin Lattice Relaxation ◽  
Axially Symmetric ◽  
Quadrupole Field ◽  
Spin Lattice ◽  
Temperature Relaxation

Abstract The spin-lattice relaxation time T1 in 103Ru has been determined on the basis of the Dirac theory and strict relativistic band structure calculations. The low temperature relaxation time T(of 103Ru in an axially symmetric quadrupole field and the quadrupole moment Q have been measured by Green and Stone using the technique of low temperature quadrupole orientation. For the usual reference value T1 T, which corresponds to relaxation in a Zeeman spectrum, they obtain 39(6) sK, which exceeds our value by 134%. This large discrepancy is attributed to the fact that the spin relaxation by direct quadrupole scattering of conduction electrons, the so-called Mitchell contribution, is dominant. According to our calculations it amounts to 81% of the total relaxation rate. This contribution could not be included in the evaluation of the experimental data.

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.

35Cl NQR Study of Thermoactivated Motions of Nitro Groups in Picryl Chloride

1996 ◽  
Vol 51 (5-6) ◽  
pp. 713-715 ◽  
Author(s):  
Igor A. Kyuntsel
Keyword(s):  
Relaxation Time ◽  
Lattice Relaxation ◽  
Lattice Relaxation Time ◽  
Rapid Decrease ◽  
Spin Lattice Relaxation ◽  
Deep Minimum ◽  
Spin Lattice ◽  
35Cl Nqr ◽  
Temperature Dependences ◽  
Picryl Chloride

Abstract The temperature dependences of the 35Cl NQR frequency (ν), spin-lattice relaxation time (T1), and spin-spin relaxation time (T2) have been studied in 2,4,6-trinitrochlorobenzene (picryl chloride) from 77 K up to the melting point (354 K). The T1(T) curve exhibits a pronounced composite mimimum near 300 K which gives evidence for the reorientations of the two ortho-NO2 groups around their two-fold symmetry axes with the activation energies of 27.4 kJ mol - 1 and 31.2 kJ mol - 1. These values can be related to the ortho-NO2 groups having the twist angles of 33° and 81°, respectively (the crystal structure of picryl chloride is known). The T2(T) dependence exhibits interesting features, too: a deep minimum about 140 K and a new rapid decrease above 270 K.

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