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: In this paper, the authors performed nuclear magnetic resonance and nuclear quadrupole resonance (NQR) measurements on the superconductor YBa{sub 2}Cu{sub 4}O{sub 8} and found that the Y, Cu, and O shift data support, for planes and chains, the validity of the single-spin fluid model.
Abstract: By performing nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR), respectively, with Cu, O, and Y isotopes in the normal state of the high-temperature superconductor YBa{sub 2}Cu{sub 4}O{sub 8}, we have found the following major results: (i) The Y, Cu, and O shift data support, for planes and chains, the validity of the {open_quotes}single-spin fluid model.{close_quotes} (ii) Around T{sup {dagger}}=180 K, {open_quotes}anomalies{close_quotes} in the temperature behavior of several NMR/NQR quantities have been detected. (iii) The anomalies do not arise from a structural phase transition; instead they reflect an electronic crossover which involves enhanced charge fluctuations in planes and chains accompanied by a charge (hole) transfer from chain to plane. (iv) As a possible mechanism of the crossover, a charge-density-wave instability is proposed. {copyright} {ital 1997} {ital The American Physical Society}
32 citations
TL;DR: In this paper, the ground state band structure, magnetic moments, charges and population numbers of electronic shells of chalcopyrite CuFeS2 using density functional theory were calculated.
Abstract: The ground state band structure, magnetic moments, charges and population numbers of electronic shells of Cu and Fe atoms have been calculated for chalcopyrite CuFeS2 using density functional theory. The comparison between our calculation results and experimental data (X-ray photoemission, X-ray absorption and neutron diffraction spectroscopy) has been made. Our calculations predict a formal oxidation state for chalcopyrite as Cu1+Fe3+S22−. However, the assignment of formal valence state to transition metal atoms appears to be oversimplified. It is anticipated that the valence state can be confirmed experimentally by nuclear magnetic and nuclear quadrupole resonance and Mossbauer spectroscopy methods.
32 citations
Patent•
15 Nov 1996TL;DR: In this article, a variable impedance spectrometer is connected to the probe and has a total Q factor therewith, which can be varied by varying the impedance without changing the electrical configuration of the probe.
Abstract: A nuclear quadrupole resonance (NQR) or nuclear magnetic resonance (NMR) apparatus which includes a probe and a variable impedance spectrometer. The probe emits a signal towards a specimen which causes the specimen to produce a resonance signal. After a recovery period from emitting the signal, the probe receives the resonance signal produced by the specimen. The variable impedance spectrometer is connected to the probe and has a total Q factor therewith. The spectrometer causes the total Q factor during the recovery period to be lower than the total Q factor before and after the recovery period by varying the impedance of the spectrometer, without changing the electrical configuration of the probe.
32 citations
TL;DR: The analysis of the 29 Si MAS NMR spectrum revealed two lineshapes whose chemical shift is consistent with two silica Q n=2,3 species as discussed by the authors. But these sites were not resolved in the IDMAS NMR spectroscopy.
Abstract: 45S5 Bioglasses of the composition 46.1 SiO 2 -2.6 P 2 O 5 -26.9 CaO-(24.4 - x) Na 2 O-xMe 2 O (Me = Li or K) have been investigated using MAS NMR and MQ-MAS NMR methods. The analysis of the 29 Si MAS NMR spectrum revealed two lineshapes whose chemical shift is consistent with two silica Q n=2,3 species. The 31 P MAS NMR spectrum reveals the effect of both Na and Ca ions. The chemical shift of the observed 31 P signal is intermediate between those of Na 3 PO 4 (near 10 ppm) and Ca 3 (PO 4 ) 2 (near 3-0 ppm) species. The 23 Na MAS NMR spectra were observed in the alkali oxide composition: 24.4 Na 2 O, 12.2 Na 2 O-12.2 K 2 O and 12.2 Na 2 O-12.2 Li 2 O. The substitution of Na with Li or K was done to determine the extend of alteration of the glass structure. This goal was best accomplished by 23 Na MQ-MAS NMR. The two-dimensional spectra revealed three sites in the 24.4 mol% Na 2 O glass. These sites were not resolved in the ID MAS NMR spectroscopy. In the mixed glasses, only two sites were obtained.
32 citations
TL;DR: In this paper, the 14N nuclear quadrupole resonance spectra for the compounds 2a, b, 3b, 4b, 5a, 6b have been obtained at 77 K and the asymmetry parameter and coupling constants extracted.
Abstract: Abstract The 14N nuclear quadrupole resonance spectra for the compounds 2a, b, 3b, 4b, 5a, b, 6b have been obtained at 77 K and the asymmetry parameter and coupling constants extracted. A comparison of these with microwave spectral results, shows that small but systematic differences occur between the solid and gaseous states. There is a high level of agreement for the observed coupling constants from NQR or MW spectra and the ab initio calculations in both magnitude and direction. This enables us to extract further principal axis data from the observed microwave spectra, and to predict with some confidence the axes and coupling magnitudes for other members of the series where incomplete determinations are available. Variations in coupling constants with structure are discussed
32 citations