scholarly journals Nuclear quadrupolar spin-lattice relaxation with realistic phonon density of states in alkali halides

2017 ◽  
Vol 95 (11) ◽  
pp. 1042-1048 ◽  
Author(s):  
Ali Chandoul
Keyword(s):  
Temperature Dependence ◽  
Density Of States ◽  
Alkali Halides ◽  
Lattice Relaxation ◽  
Debye Model ◽  
Spin Lattice Relaxation ◽  
Phonon Density ◽  
Phonon Density Of States ◽  
Temperature Range ◽  
Spin Lattice

The nuclear quadrupolar spin-lattice relaxation times T1 have been calculated in alkali halides, whereby the phonon densities of states have been extracted from the shell model lattice dynamics. The calculations at room temperature were performed on 79Br in KBr, NaBr, and RbBr; 23Na in NaI, NaCl, and NaBr; 35Cl in NaCl and KCl; and 127I in NaI and KI. The obtained values of relaxation time T1 are an order of magnitude smaller than those calculated with the Debye-model phonon density of states and agree well with experiments. The temperature dependence of acoustic and optical phonon contributions to the nuclear relaxation rate (first-order Raman phonon process) are carried out in the temperature range 20 to 300 K for 23Na and 127I in NaI. The role of optical phonons becomes important from 77 K on; the temperature dependence of T1 agrees with experimental data throughout most of the temperature range studied (77–300 K), while differing quantitatively from the predictions obtained on the basis of the Debye model.

scholarly journals Isotope Effects on Deuterium Spin-Lattice Relaxation in H2O/D2O Mixtures

1985 ◽  
Vol 40 (11) ◽  
pp. 1085-1095
Author(s):  
Masato Kakihana ◽  
Makoto Okamoto ◽  
Tadashi Nagumo
Keyword(s):  
Temperature Dependence ◽  
Isotope Effects ◽  
Activation Parameters ◽  
Lattice Relaxation ◽  
Deuterium Atom ◽  
Spin Lattice Relaxation ◽  
Rate Theory ◽  
Atom Fraction ◽  
Temperature Range ◽  
Spin Lattice

The deuterium spin-lattice relaxation time, T1, of H2O/D2O mixtures is measured at 298.2 K. The relaxation rate, T1-1, is found to increase with increasing deuterium atom fraction, n, the plot of T1-1 vs. n exhibiting a small depature from linearity. A general equation T1-1 (n) for the H2O/D2O system is formulated. The temperature dependence of T1 is investigated in the temperature range 278.2 K to 298.2 K for n = 6.8 x 10-3, 6.8 x 10-2, 0.244, 0.500, and 0.997. On the assumption that the electric field gradient parameters (e2 q Q/h and δ) are independent of n and temperature, an effective correlation time, τc,eff, is derived from the T1 data. Relatively large isotope effects on τc,eff are found; possible reasons for the existence of such isotope effects are discussed in terms of a simple Debye model. The mean activation enthalpy (Δ≠ H) and entropy (Δ≠ S) for the relaxation process within the temperature range studied are derived on the basis of Eyring's absolute rate theory and the temperature dependence of τc,eff. Both activation parameters are found to increase linearly with n: Δ≠ H/kJ mol-1 = 18.2 + 2.46 n, Δ≠ S/J K-1 mol-1 = 37.5 + 6.77 n.

Bonded Hydrogen and Trapped H2 in a-Si1−xGex:H Alloys

1989 ◽  
Vol 149 ◽  
Author(s):  
E. J. Vanderheiden ◽  
G. A. Williams ◽  
P. C. Taylor ◽  
F. Finger ◽  
W. Fuhs
Keyword(s):  
Temperature Dependence ◽  
Molecular Hydrogen ◽  
Relaxation Times ◽  
Lattice Relaxation ◽  
Spin Lattice Relaxation ◽  
Spin Lattice ◽  
H Nmr ◽  
Local Environments

ABSTRACT1H NMR has been employed to study the local environments of bonded hydrogen and trapped molecular hydrogen (H2) in a series of a-Si1−xGex:H alloys. There is a monotonic decrease of bonded hydrogen with increasing x from ≈ 10 at. % at x = 0 (a-Si:H) to ≈ 1 at. % at x = 1 (a-Ge:H). The amplitude of the broad 1H NMR line, which is attributed to clustered bonded hydrogen, decreases continuously across the system. The amplitude of the narrow 1H NMR line, which is attributed to bonded hydrogen essentially randomly distributed in the films, decreases as x increases from 0 to ≈ 0.2. From x = 0.2 to x ≈ 0.6 the amplitude of the narrow 1H NMR line is essentially constant, and for x ≥ 0.6 the amplitude decreases once again. The existence of trapped H2 molecules is inferred indirectly by their influence on the temperature dependence of the spin-lattice relaxation times, T1. Through T1, measurements it is determined that the trapped H2 concentration drops precipitously between x = 0.1 and x = 0.2, but is fairly constant for 0.2 ≤ x ≤ 0.6. For a-Si:H (x = 0) the H2 concentration is ≈ 0.1 at. %, while for x ≥ 0.2 the concentration of H2 is ≤ 0.02 at. %.

Calculation of NQR v's and T1-1' s being proportional to T4 and T5 , respectively

1990 ◽  
Vol 45 (3-4) ◽  
pp. 536-540
Author(s):  
Mariusz Máckowiak ◽  
Costas Dimitropoulos
Keyword(s):  
Temperature Dependence ◽  
Relaxation Rate ◽  
Spin System ◽  
Low Frequency ◽  
Lattice Relaxation ◽  
Spin Lattice Relaxation ◽  
Lattice Vibrations ◽  
Spin Lattice ◽  
Simplifying Assumptions ◽  
The One

Abstract The second-order Raman phonon process for a multilevel spin system is shown to give a quadru-polar spin-lattice relaxation rate T1-1varying as T5 at very low temperatures. This relaxation rate for quadrupole spins is similar to the one discussed for a paramagnetic spin system having a multilevel ground state. The temperature dependence of T1 is discussed on the basis of some simplifying assumptions about the nature of the lattice vibrations in the Debye approximation. This type of relaxation process has been observed below 20 K in tetramethylammonium hydrogen bis-trichloroacetate for the 35Cl T1-1 . Below 20 K the NQR frequency in the same crystal reveals a T4 temperature dependence due to the induced modulations of the vibrational and librational coordinates by the low-frequency acoustic phonons.

NQR Relaxation Studies on Halogenomethyl Groups in Halogenoacetates

1998 ◽  
Vol 53 (6-7) ◽  
pp. 480-483 ◽  
Author(s):  
Maria Zdanowska-Fnjczek
Keyword(s):  
Room Temperature ◽  
Relaxation Times ◽  
Lattice Relaxation ◽  
Spin Lattice Relaxation ◽  
Effect Of Temperature ◽  
Relaxation Theory ◽  
Temperature Range ◽  
Spin Lattice ◽  
Relaxation Studies

Abstract The effect of temperature on the chlorine NQR spin-lattice relaxation times in CsH(ClH2-CCOO)2 , KH(Cl3 CCOO) 2 and N(CH3)4 H(ClF2CCOO)2 has been studied in the temperature range 77 K to room temperature. The results were discussed on the basis of NQR relaxation theory.

35Cl NQR Studies of Bismuth Trichloride

1997 ◽  
Vol 52 (8-9) ◽  
pp. 614-620
Author(s):  
P. K. Babu ◽  
J. Ramakrishna
Keyword(s):  
Temperature Dependence ◽  
Lattice Relaxation ◽  
Lattice Relaxation Time ◽  
Positive Temperature Coefficient ◽  
Spin Lattice Relaxation ◽  
Positive Temperature ◽  
Lattice Vibrations ◽  
Spin Lattice ◽  
Quadrupole Resonance ◽  
35Cl Nqr

Abstract The temperature dependence of the 35Cl nuclear quadrupole resonance (NQR) frequency and spin lattice relaxation time (T1) are studied in crystalline BiCl3 , in the range 40-300 K. The positive temperature coefficient observed for one of the 35Cl resonances is explained in terms of the strong intermolecular interactions that exist in this compound. Variation of with temperature is found to be similar at the chemically inequivalent halogen sites. Semiclassical descriptions based on torsional oscillator dynamics are found to be inadequate for explaining the spin lattice relaxation. T1 (T) data follow an AT2 + BT3 type behaviour, indicating that the anharmonic nature of the lattice vibrations plays a significant role in determining the temperature dependence of T1 at high temperatures.

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