Topic
Nuclear quadrupole resonance
About: Nuclear quadrupole resonance is a research topic. Over the lifetime, 3531 publications have been published within this topic receiving 38801 citations. The topic is also known as: Nuclear quadrupole resonance spectroscopy & NQR.
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TL;DR: It is shown that a simple model based on the anharmonicity of the hydrogen bond potential fails to describe the temperature dependence of the couplings even qualitatively, and the inclusion of fluctuations and disorder in terms of atomic motion of the surrounding molecules turns out to be important to obtain the correct magnitude of the temperature effect.
Abstract: We present an analysis of the effect of finite temperatures on the deuteron nuclear quadrupole coupling constants in a strongly hydrogen-bonded molecular crystal by means of first-principles Car-Parrinello molecular-dynamics simulations. Our findings agree well with experiments and provide a microscopic explanation of the anomalous increase of the quadrupole coupling in this class of systems. We show that a simple model based on the anharmonicity of the hydrogen bond potential fails to describe the temperature dependence of the couplings even qualitatively. Instead, the inclusion of fluctuations and disorder in terms of atomic motion of the surrounding molecules turns out to be important to obtain the correct magnitude of the temperature effect.
26 citations
TL;DR: In this article, the authors reported 139La, 57Fe and 75As NMR and NQR measurements on powders of the new LaO1?xFxFeAs superconductor for x=0 and 0.1 at temperatures up to 480?K.
Abstract: We report 139La, 57Fe and 75As nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR) measurements on powders of the new LaO1?xFxFeAs superconductor for x=0 and 0.1 at temperatures up to 480?K, and compare our measured NQR spectra with local density approximation (LDA) calculations. For all three nuclei in the x=0.1 material, it is found that the local Knight shift increases monotonically with an increase in temperature, and scales with the macroscopic susceptibility, suggesting a single magnetic degree of freedom. Surprisingly, the spin lattice relaxation rates for all nuclei also scale with one another, despite the fact that the form factors for each site sample different regions of q-space. This result suggests a lack of any q-space structure in the dynamical spin susceptibility that might be expected in the presence of antiferromagnetic correlations. Rather, our results are more compatible with simple quasi-particle scattering. Furthermore, we find that the increase in the electric field gradient at the As cannot be accounted for by LDA calculations, suggesting that structural changes, in particular the position of the As in the unit cell, dominate the NQR response.
26 citations
TL;DR: The numbers of electrons donated by the organic iodine atom to Ag(+) have been estimated and these indicate that the bonding to the cation is weak but not insignificant, as expected from hard-soft acid-base principles.
Abstract: 35Cl, (79,81)Br, and (127)I NQR (nuclear quadrupole resonance) spectroscopy in conjunction with X-ray crystallography is potentially one of the best ways of characterizing secondary bonding of metal cations such as Ag(+) to halogen donor atoms on the surfaces of very weakly coordinating anions. We have determined the X-ray crystal structure of Ag(O(3)SCH(2)Cl) (a = 13.241(3) A; b = 7.544(2) A; c = 4.925(2) A; orthorhombic; space group Pnma; Z = 4) and compared it with the known structure of Ag(O(3)SCH(2)Br) (Charbonnier, F.; Faure, R.; Loiseleur, H. Acta Crystallogr., Sect. B 1978, 34, 3598-3601). The halogen atom in each is apical (three-coordinate), being weakly coordinated to two silver ions. (127)I NQR studies on Ag(O(3)SCH(2)I) show the expected NQR consequences of three-coordination of iodine: substantially reduced NQR frequencies nu(1) and nu(2) and a fairly small NQR asymmetry parameter eta. The reduction of the halogen NQR frequency of the coordinating halogen atom in Ag(O(3)SCH(2)X) becomes more substantial in the series X = Cl < Br < I, indicating that the coordination to Ag(+) strengthens in this series, as expected from hard-soft acid-base principles. The numbers of electrons donated by the organic iodine atom to Ag(+) have been estimated; these indicate that the bonding to the cation is weak but not insignificant. We have not found any evidence for the bonding of these organohalogen atoms to another soft-acid metal ion, thallium. A scheme for recycling of thallium halide wastes is included.
26 citations
TL;DR: In this paper, the authors used doule resonance with coupled multiplets to measure the nuclear quadrupole resonance spectra of 17O at both the C�O and COH sites.
26 citations
TL;DR: In this article, the nuclear-spin lattice relaxation rate of CeRu 2 has been investigated using an NQR technique in zero magnetic field, and it is considered that the impurity scattering averages out the anisotropy of the energy gap.
Abstract: Superconducting characteristics of CeRu 2 have been investigated by systematic measurements of the nuclear-spin lattice relaxation rate, 1/ T 1 of 101 Ru on pure and impurity-substituted CeRu 2 , employing an NQR technique in zero magnetic field. (1/ T 1 ) for CeRu 2 shows a broad coherence plateau just below T c followed by an exponential decrease well below T c . By contrast, a distinct coherence peak of (1/ T 1 ) has been found just below T c for the impurity-substituted CeRu 2 , even though La- and Al-substitutions for the Ce and Ru sites make T c slightly increase and decrease, respectively. It is considered that the impurity scattering averages out the anisotropy of the energy gap, in good agreement with the theory of dirty superconductors by Anderson. 101 (1/ T 1 T ) in the normal state, which is in proportion to the square of the density of states at the Fermi level, N 2 ( E F ), is found to decrease with the Al content. The suppression in T c by substituting nonmagnetic Al impurity for the Ru sit...
26 citations