Showing papers on "Nuclear quadrupole resonance published in 2015"
TL;DR: In the superconducting state, 1/T(1) decreases rapidly below T(c) without a Hebel-Slichter peak, and follows a T(5) variation below T∼3 K, which points to unconventional superconductivity with point nodes in the gap function.
Abstract: We report (75)As nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR) studies on the superconductor Rb(2)Cr(3)As(3) with a quasi-one-dimensional crystal structure. Below T∼100 K, the spin-lattice relaxation rate (1/T(1)) divided by temperature, 1/T(1)T, increases upon cooling down to T(c)=4.8 K, showing a Curie-Weiss-like temperature dependence. The Knight shift also increases with decreasing temperature. These results suggest ferromagnetic spin fluctuation. In the superconducting state, 1/T(1) decreases rapidly below T(c) without a Hebel-Slichter peak, and follows a T(5) variation below T∼3 K, which points to unconventional superconductivity with point nodes in the gap function.
61 citations
TL;DR: The absence of a coherence effect in 1/T(1) in the superconducting state provides evidence that CrAs is the first Cr-based unconventional superconductor.
Abstract: Pressure-induced superconductivity was recently discovered in the binary helimagnet CrAs. We report the results of measurements of nuclear quadrupole resonance for CrAs under pressure. In the vicinity of the critical pressure P(c) between the helimagnetic (HM) and paramagnetic (PM) phases, a phase separation is observed. The large internal field remaining in the phase-separated HM state indicates that the HM phase disappears through a strong first-order transition. This indicates the absence of a quantum critical point in CrAs; however, the nuclear spin-lattice relaxation rate 1/T(1) reveals that substantial magnetic fluctuations are present in the PM state. The absence of a coherence effect in 1/T(1) in the superconducting state provides evidence that CrAs is the first Cr-based unconventional superconductor.
47 citations
TL;DR: This work proposes solid ReO3 as a new rhenium SSNMR chemical shift standard due to its reproducible and sharp (185/187)Re NMR resonances, and establishes a correlation between the tetrahedral shear strain parameter (|ψ|) and the nuclear electric quadrupolar coupling constant (CQ), which enables the refinement of the structure of ND4ReO4.
Abstract: Advances in solid-state nuclear magnetic resonance (SSNMR) methods, such as dynamic nuclear polarization (DNP), intricate pulse sequences, and increased applied magnetic fields, allow for the study of systems which even very recently would be impractical. However, SSNMR methods using certain quadrupolar probe nuclei (i.e., I > 1/2), such as 185/187Re remain far from fully developed due to the exceedingly strong interaction between the quadrupole moment of these nuclei and local electric field gradients (EFGs). We present a detailed high-field (B0 = 21.1 T) experimental SSNMR study on several perrhenates (KReO4, AgReO4, Ca(ReO4)2·2H2O), as well as ReO3 and Re2(CO)10. We propose solid ReO3 as a new rhenium SSNMR chemical shift standard due to its reproducible and sharp 185/187Re NMR resonances. We show that for KReO4, previously poorly understood high-order quadrupole-induced effects (HOQIE) on the satellite transitions can be used to measure the EFG tensor asymmetry (i.e., ηQ) to nearly an order-of-magnitude greater precision than competing SSNMR and nuclear quadrupole resonance (NQR) approaches. Samples of AgReO4 and Ca(ReO4)2·2H2O enable us to comment on the effects of counter-ions and hydration upon Re(VII) chemical shifts. Calcium-43 and 185/187Re NMR tensor parameters allow us to conclude that two proposed crystal structures for Ca(ReO4)2·2H2O, which would be considered as distinct, are in fact the same structure. Study of Re2(CO)10 provides insights into the effects of Re–Re bonding on the rhenium NMR tensor parameters and rhenium oxidation state on the Re chemical shift value. As overtone NQR experiments allowed us to precisely measure the 185/187Re EFG tensor of Re2(CO)10, we were able to measure rhenium chemical shift anisotropy (CSA) for the first time in a powdered sample. Experimental observations are supported by gauge-including projector augmented-wave (GIPAW) density functional theory (DFT) calculations, with NMR tensor calculations also provided for NH4ReO4, NaReO4 and RbReO4. These calculations are able to reproduce many of the experimental trends in rhenium δiso values and EFG tensor magnitudes. Using KReO4 as a prototypical perrhenate-containing system, we establish a correlation between the tetrahedral shear strain parameter (|ψ|) and the nuclear electric quadrupolar coupling constant (CQ), which enables the refinement of the structure of ND4ReO4. Shortcomings in traditional DFT approaches, even when including relativistic effects via the zeroth-order regular approximation (ZORA), for calculating rhenium NMR tensor parameters are identified for Re2(CO)10.
18 citations
TL;DR: In this article, field-swept 33 S NMR spectra of a cyclic octaatomic molecule of elemental sulfur, α-S 8, were obtained at a Larmor frequency of 16.2 MHz and using a superconducting magnet at between 6.32 and 0.50 T.
17 citations
TL;DR: In this article, the authors used nuclear quadrupole resonance to probe microscopically the response of a prototypical quantum critical metal to substitutions of small amounts of Sn and Cd for In.
Abstract: Chemical substitutions are used commonly to tune a magnetic transition to zero temperature, but the resulting non-Fermi-liquid (NFL) behavior is nonuniversal. We have used nuclear quadrupole resonance to probe microscopically the response of a prototypical quantum critical metal ${\mathrm{CeCoIn}}_{5}$ to substitutions of small amounts of Sn and Cd for In. These substituents induce very different local electronic environments as observed by site-dependent spin lattice relaxation rates $1/{T}_{1}$ that influence the NFL behavior. The effects found here illustrate the need for care in interpreting NFL properties determined by macroscopic measurements.
17 citations
TL;DR: A new polymorphic crystal form of piroxicam was discovered while preparing crystalline samples for (14) N nuclear quadrupole resonance (NQR) analysis, and a consistent set of measured frequencies and calculated characteristic quadrupoles parameters found are convincing evidence that it is a new form.
16 citations
TL;DR: In this article, 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 Cu$^{1+}$Fe$^{3+}$S$_{2}$$^{2-}$. 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.
16 citations
TL;DR: In this article, the 73Ge-NMR/nuclear quadrupole resonance (NQR) results for the ferromagnetic superconductor URhGe were determined experimentally.
Abstract: We report on the 73Ge-nuclear magnetic resonance (NMR)/nuclear quadrupole resonance (NQR) results for the ferromagnetic (FM) superconductor URhGe. The magnitude and direction of the internal field, Hint, and the parameters of the electric field gradient at the Ge site were determined experimentally. By using powdered polycrystalline samples oriented by different methods, the field dependences of NMR shift and nuclear spin relaxation rates for H0 || c (easy axis) and H0 || b were obtained. From the NMR shifts for H0 || b, we confirmed a gradual suppression of the Curie temperature and observed a phase separation near the spin reorientation. The observation of the phase separation gives microscopic evidence that the spin reorientation under H0 || b is of first order at low temperatures. The nuclear spin–lattice relaxation rate 1/T1 indicates that the magnetic fluctuations are suppressed for H0 || c, whereas the fluctuations remain strongly for H0 || b. The enhancements of both 1/T1T and the nuclear spin–spi...
16 citations
TL;DR: In this article, the relationship between electronic structure and corrosion inhibition efficiencies of protonated and non-protonated forms of 3-formyl 8-hydroxy quinoline and 5-naphthylazo-8-hydroxquinoline (5NA8HQ) in acidic media in gas and solvent phase was investigated.
Abstract: Density functional theory B3LYP and Hartree–Fock methods with 6-311++G** basis set were utilized to study the relationship between electronic structure and corrosion inhibition efficiencies of protonated and non-protonated forms of 3-formyl 8-hydroxy quinoline and 5-naphthylazo-8-hydroxyquinoline (5NA8HQ) in acidic media in gas and solvent phase. Quantum chemical parameters including highest molecular orbital energy, lowest unoccupied molecular orbital energy, energy gap (ΔE
g), the fraction of electrons transferred (ΔN), and energy change during charge transfer (ΔE) were calculated. Protonation energy calculations showed that the favorite protonation site of 5NA8HQ is the N12 position, which is confirmed by the result of previously reported experimental investigations. Calculations on the inhibitor/iron system were performed using the B3LYP/6-311++G** method and found that azo nitrogens of 5NA8HQ have better interaction with iron. Also, nuclear quadrupole resonance parameters indicate that azo nitrogens (N11 and N12) are the best sites for interaction with iron.
15 citations
TL;DR: The results of this study illustrate the potential of NQR as promising technique in applications such as detection and authentication of counterfeit medicines.
Abstract: In this paper, we report on the identification of batches of analgesic paracetamol (acetaminophen) tablets using nitrogen-14 nuclear quadrupole resonance spectroscopy ((14)N NQR). The high sensitivity of NQR to the electron charge distribution surrounding the quadrupolar nucleus enables the unique characterization of the crystal structure of the material. Two hypothesis were tested on batches of the same brand: the within the same batch variability and the difference between batches that varied in terms of their batch number and expiry date. The multivariate analysis of variance (MANOVA) did not provide any within-batches variations, indicating the natural deviation of a medicine manufactured under the same conditions. Alternatively, the statistical analysis revealed a significant discrimination between the different batches of paracetamol tablets. Therefore, the NQR signal is an indicator of factors that influence the physical and chemical integrity of the material. Those factors might be the aging of the medicine, the manufacturing, or storage conditions. The results of this study illustrate the potential of NQR as promising technique in applications such as detection and authentication of counterfeit medicines.
14 citations
TL;DR: In this article, the bulk magnetic susceptibility and 93Nb nuclear quadrupole resonance (NQR) in the Pr-based caged compound PrNb2Al20 were analyzed and the results showed that no symmetry-breaking magnetic dipole order occurs down to 75 mK. The frequency dependence of 1/T1 is attributed to the magnetic fluctuation due to the hyperfineenhanced 141Pr nuclear moment inherent in the nonmagnetic Γ3 CEF ground state.
Abstract: We report measurements of bulk magnetic susceptibility and 93Nb nuclear quadrupole resonance (NQR) in the Pr-based caged compound PrNb2Al20. By analyzing the magnetic susceptibility and magnetization, the crystal electric field (CEF) level scheme of PrNb2Al20 is determined to be Γ3(0 K)–Γ4(21.32 K)–Γ5(43.98 K)–Γ1(51.16 K) within the framework of the localized 4f electron picture. The 93Nb-NQR spectra exhibit neither spectral broadening nor spectral shift upon cooling down to 75 mK. The 93Nb-NQR spin–lattice relaxation rate 1/T1 at 5 K depends on the frequency and remains almost constant below 5 K. The frequency dependence of 1/T1 is attributed to the magnetic fluctuation due to the hyperfine-enhanced 141Pr nuclear moment inherent in the nonmagnetic Γ3 CEF ground state. The present NQR results provide evidence that no symmetry-breaking magnetic dipole order occurs down to 75 mK. Also, considering an invariant form of the quadrupole and octupole couplings between a 93Nb nucleus and Pr 4f electrons, Pr 4f qu...
TL;DR: In this article, the authors carried out nuclear magnetic resonance (NMR) and nuclear quadrupole resonance measurements on ThRu2Si2 and LaRu 2Si2, which are the nonmagnetic references of the intriguing heavy fermion URu2 Si2.
Abstract: We have carried out nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR) measurements on ThRu2Si2 and LaRu2Si2, which are the nonmagnetic references of the intriguing heavy fermion URu2Si2 The comparisons of URu2Si2 with the reference materials allow us to analyze the already known NMR and NQR data on URu2Si2 phenomenologically and semiquantitatively The study of 101Ru-NQR frequency suggests the relatively close electronic configuration of URu2Si2, including the valence of the actinide ion, to that of the tetravalent ThRu2Si2 at high temperatures, as well as the delocalization of 5f electrons at low temperatures Ising-like spin fluctuations along the c-axis were brought to light by 29Si-NMR data in the so-called hidden order phase of URu2Si2 The unique magnetic property is plausibly associated with the mechanism of the unconventional superconductivity
TL;DR: In this article, the nuclear quadrupole resonance signal on the Zn site in nearly optimally doped YBa2Cu3O6.92, when Cu is substituted by 3% of isotopically pure 67Zn, was measured.
Abstract: We measure the nuclear quadrupole resonance signal on the Zn site in nearly optimally doped YBa2Cu3O6.92, when Cu is substituted by 3% of isotopically pure 67Zn. We observe that Zn creates large insulating islands, confirming two earlier conjectures: that doping provokes an orbital transition in the CuO2 plane, which is locally reversed by Zn substitution, and that the islands are antiferromagnetic. Also, we find that the Zn impurity locally induces a breaking of the D4 symmetry. Cluster and DFT calculations show that the D4 symmetry breaking is due to the same partial lifting of degeneracy of the nearest-neighbor oxygen sites as in the LTT transition in BaxCuO4, similarly well-known to strongly suppress superconductivity (SC). These results show that in-plane oxygen 2p5 orbital configurations are principally involved in the metallicity and SC of all high-Tc cuprates, and provide a qualitative symmetry-based constraint on the SC mechanism.
TL;DR: In this paper, the frequency-swept solid-state [ 33 S]-diphenyl disulfide NMR spectra were obtained at extremely low magnetic fields, 0.06 and 0.10 T.
TL;DR: In this paper, the authors describe the implementation of basic quantum gates and their applications on the creation and manipulation of pseudopure states using linearly polarized radiofrequency pulses under static magnetic field perturbation.
Abstract: Nuclear magnetic resonance (NMR) has been widely used in the context of quantum information processing (QIP). However, despite the great similarities between NMR and nuclear quadrupole resonance (NQR), no experimental implementation for QIP using NQR has been reported. We describe the implementation of basic quantum gates and their applications on the creation and manipulation of pseudopure states using linearly polarized radiofrequency pulses under static magnetic field perturbation. The NQR quantum operations were implemented using a single-crystal sample of $$\hbox {KClO}_{3}$$KClO3 and observing $$^{35}\hbox {Cl}$$35Cl nuclei, which possess spin 3/2 and give rise to a two-qubit system. The results are very promising and indicate that NQR can be successfully used for performing fundamental experiments in QIP. One advantage of NQR in comparison with NMR is that the main interaction is internal to the sample, which makes the system more compact, lowering its cost and making it easier to be miniaturized to solid-state devices. Furthermore, as an example, the study of squeezed spin states could receive relevant contributions from NQR.
TL;DR: The results of an experimental study of phase transitions in molecular crystal of paradichlorobenzene by the nuclear quadrupole resonance relaxometry method with inversion of the Laplace transform are described in this paper.
Abstract: The results of an experimental study of phase transitions in molecular crystal of paradichlorobenzene by the nuclear quadrupole resonance relaxometry method with inversion of the Laplace transform are described in the article. The distributions of relaxation times T
1, T
1ρ
and $$T_{2}^{*}$$
for α- and β-phases of p-C6H4Cl2 are measured. It is determined, that spin–spin relaxation times have unimodal distributions for α- and β-phases, and spin–lattice relaxation times, including in rotating system of coordinates—multimodal distributions. It has been shown that spontaneous β → α phase transition does not arise in the porous material preliminary impregnated with the fused sample and the β-phase is steadily retained.
TL;DR: In this article, structural, electronic, and hyperfine properties of pure and Cd-doped lanthanum sesquioxide (La2O3) with the hexagonal structure (A-phase) were analyzed.
TL;DR: In this article, the properties of entanglement between two qubits are studied and the concurrence, the entropy, and fluctuations of the entropy in the pure and mixed states are analyzed.
Abstract: A single spin- possessing a quadrupole moment and placed in a non-uniform electric field, is isomorphic to a system of two spins of which can be represented as two qubits. To create these qubits, the degeneracy of the energy levels is removed by applying two radio-frequency fields with different phases and directions. The properties of entanglement between two qubits are studied. We analyze the concurrence, the entropy of entanglement, and fluctuations of the entropy in the pure and mixed states. Concurrence and entropy of entanglement in a mixed state increase with decreasing temperature and approach to their values in a pure state. For a nucleus Cu in high temperature superconductor the estimation of the temperature, at which entanglement appears, gives 0.8 μK.
TL;DR: In this article, a Kohn-Sham DFT + U calculation was performed on La 2CuO 4 for the first time, and the nuclear quadrupole resonance (NQR) signal on the Zn site itself was measured.
Abstract: Sr doping in La 2CuO 4 is investigated by a Kohn-Sham DFT + U calculation. The Sr charge remains highly localized, confirming earlier calculations. The bulk of the charge in the nodal metal is delocalized in situ in the CuO 2 plane. Standard Kohn-Sham DFT+U reproduces the metal-insulator transition and growth of Fermi-surface arcs, as observed in angle-resolved photoemission spectroscopy (ARPES), when not restricted to the paramagnetic solution space. Substituting planar Cu by isotopically pure 67Zn in yttrium barium copper oxide (YBCO), we measure the nuclear quadrupole resonance (NQR) signal on the Zn site itself for the first time. Zn creates large insulating islands, extending at least to the nearest-neighbor Cu site, thus confirming that doping induces an orbital delocalization transition in the plane, which is locally reversed by Zn substitution. Calculations show that the D4 symmetry-breaking observed in NQR is due to the same partial lifting of degeneracy of the nearest-neighbor oxygen sites as in the low temperature tetragonal (LTT) transition in lanthanum strontium copper oxide (LSCO).
TL;DR: In this article, a model of a saddle-shaped coil physical structure was used to calculate the magnetic field topology of a nuclear qaudrupole resonance spectrometer and the relative volume of coil work area was determined, which makes 28.12% of its full volume.
Abstract: A topology of high-frequency field intensity in the work area of a saddle-shaped coil for a nuclear qaudrupole resonance spectrometer was studied. With a view to determine magnetic field topology, a computational domain was created which is a model of a saddle-shaped coil physical structure. Finite element method was used to perform numerical simulation in COMSOL Multiphysics software. According to the results of calculations performed and the field maps obtained, the relative volume of coil work area was determined which makes 28.12% of its full volume. For such a volume the recommended size of samples under study is 12× 18× 10mm3.
TL;DR: The use of ESEEM to study the slow motion of deuterium nuclei using their nuclear quadrupole resonance (NQR) line shapes and it was shown that four-pulse ESE EM allowed measurement of the nearly pure (2)H NQR line shape.
Journal Article•
TL;DR: In this paper, the interaction between oxygen molecules and the outside and inside surfaces of pristine and Ge-doped (4,4) armchair and (6,0) zigzag models of aluminum phosphide nanotubes (AlPNTs) was systematically investigated using density function theory.
Abstract: In this research the interaction between oxygen molecules and the outside and inside surfaces of pristine and Ge-doped (4,4) armchair and (6,0) zigzag models of aluminum phosphide nanotubes (AlPNTs) was systematically investigated using density function theory. Structural parameters, adsorption energy, quantum parameters, HOMO/LUMO orbitals, and nuclear quadrupole resonance (NQR) parameters were calculated for all models of AlPNTs. The aim of this work was to investigate the effects of Ge doping and O$_{2}$ adsorption on the electrical and structural parameters of (4,4) armchair and (8,0) zigzag models of AlPNTs. The results revealed that adsorption energies for all models were negative with exothermic chemical bonding. By doping Ge in spite of the B52 site of (4,4) armchair and (6,0) zigzag models the adsorption energy increased significantly from pristine values and therefore Ge doping increased the reactivity of the nanotubes to O$_{2}$ adsorption. The NQR results showed that in AlPNTs Al atoms at the edges of nanotubes played a significant role in determining the electronic behaviors of AlPNTs and the average values of C$_{Q}$ ($^{27}$Al) and $\eta_{Q}$ for the O$_{2}$ attached on (4,4) armchair and (6,0) zigzag AlPNTs were higher than those of the pristine model. Analysis of the electronic properties indicated that adsorption of O$_{2}$ reduced the energy gap of AlPNTs. Quantum molecular results showed that the global hardness ($\eta )$ of Ge-doped models was smaller than that of other models.
TL;DR: The findings enhance the detection capabilities of NQR based analysers for online measurement applications and may aid to control arsenic and antimony concentrations in metal processing stages.
TL;DR: A spin-spin relaxation time enhancement of up to five in synthetic powders in the presence of a weak external static magnetic field is observed, of interest with regard to signal-to-noise ratio improvement for materials characterization applications where broad NQR absorption lines are excited with wideband pulse sequences.
TL;DR: In this article, the influence of the environment surrounding the surface of the crystallites of a KClO3 powder on the distribution of the spin-spin and spin-lattice relaxation times for 35Cl nuclear quadrupole resonance is described.
Abstract: Abstract The results of the experimental study of the influence of the environment surrounding the surface of the crystallites of a KClO3 powder on the distribution of the spin–spin and spin–lattice relaxation times for 35Cl nuclear quadrupole resonance are described. It was found that the distributions of the spin–lattice relaxation times are unimodal and distributions of the spin–spin relaxation times are bimodal for all samples we studied. T1 – T2 and T1ρ – T2 correlations by means of the two-dimensional (2D) inverse Laplace transform are obtained. The efficiency of the method for the study of surface phenomena in solids is demonstrated.
TL;DR: (14)N NQR spectroscopy is used to quantitatively analyze hydration of a model compound, 5-aminotetrazole, and can achieve errors <1% of the total amount, provided good temperature stabilization is implemented, which then allows long experimental times.
Abstract: Hydration is a quite common process in pharmaceutical solids. Sometimes it is desirable, as it stabilizes the crystal structure; in other cases it is unwanted, as it changes the physical and chemical properties of drugs. We here use (14)N NQR spectroscopy to quantitatively analyze hydration of a model compound, 5-aminotetrazole. (14)N NQR has some great advantages compared to other routinely used techniques to study hydration, like a very simple spectrum, single point calibration, and no need for special sample preparation, but the method's great disadvantage is a rather small sensitivity. Nevertheless, here we demonstrate that (14)N NQR, although being significantly less sensitive than XRD, NIR, and also (35)Cl NQR, is still capable of providing excellent quantitative accuracies. We can achieve errors <1% of the total amount, provided good temperature stabilization is implemented, which then allows long experimental times. We also present results obtained with a SLSE pulse sequence, which is a less robust approach but allows the use of much shorter measuring times (∼200×) and could be used for quantitative real time monitoring of hydration or dehydration.
TL;DR: In this paper, the complete 14N nuclear quadrupole resonance (NQR) spectrum of ammonium nitrate was recorded using two double resonance techniques, double contact cross relaxation and zero field NQR.
Abstract: The complete 14N nuclear quadrupole resonance (NQR) spectrum of ammonium nitrate is presented recorded using two double resonance techniques – double contact cross relaxation and zero field NQR. The spectra gave the quadrupole coupling constant (Qcc) and asymmetry parameter (η) values for the nitro of 611 kHz, 0.229 and that for the ammonium nitrogen of 242 kHz, 0.835. The three relaxation transition probabilities have been determined for both the nitro and ammonium nitrogen atoms. The bi-exponential relaxation times (T 1) were measured at 295 K. The values for nitro are 16.9 s and 10.5 s and that of the ammonium are 23.0 s and 16.4 s.
TL;DR: In this paper, the authors used pulsed 63,65Cu nuclear quadrupole resonance at room temperature to study the semiconductor compound CuAlO2 with a delafossite crystal structure.
Abstract: We have used pulsed 63,65Cu nuclear quadrupole resonance at room temperature to study the semiconductor compound CuAlO2 with a delafossite crystal structure, and we have determined the quadrupole frequency νQ = 28.12 MHz and the asymmetry parameter η ~ 0, which we used to study the features of the electron density distribution in the vicinity of the quadrupolar nucleus. In order to take into account the influence of correlation effects on the electric field gradient, we carried out ab initio calculations within the density functional theory (DFT) approximation using a set of correlation functionals VWN1RPA, VWN5, PW91LDA, CPW91, and B3LYP1. We mapped the electron density distribution in the vicinity of the quadrupolar copper nucleus for the Cu7Al6o
14
‐ 1
cluster and we calculated the size of the LUMO–HOMO gap, Δ ~ 3.33 eV. We established the anisotropy of the spatial electron density distribution. Based on analysis of the electron density distribution obtained, we suggest that the bond in CuAlO2 is not purely covalent.
01 Jan 2015
TL;DR: A review of the state of the art in NQR, analyzing its relevance to the landmine detection problem and concluding about unsolved problems that could be the focus of future research is presented in this paper.
Abstract: Nuclear quadrupole resonance (NQR) is a spectroscopic technique that can detect explosives of high chemical specificity and therefore it is very suitable for the landmine detection problem. There are several factors affecting the relation of noise signal ratio with NQR: molecular dynamics of relaxation, interference signals, thermal noise, explosive amount, distance, temperature and the design of the detecting system. Literature has searched ways for solving one or more of these factors, but since not all the work has been focused on landmine detection, many have only been tested in simulation or with data obtained under controlled laboratory conditions, where the detection is not remote (there is no separation between the sample and the detection system). This paper makes a review of the state of art in NQR, analyzing its relevance to the landmine detection problem and concluding about unsolved problems that could be the focus of future research.
18 Mar 2015
TL;DR: In this paper, the authors reported a study of 93Nb-and 27Al-NMR and nuclear quadrupole resonance (NQR) in a praseodymium-based compound PrNb2Al20, where the observed NMR line at around 3 T and 30 K shows a superposition of typical powder patterns of one Nb signal and at least two Al signals.
Abstract: We report a study of 93Nb- and 27Al-nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR) in a praseodymium based compound PrNb2Al20. The observed NMR line at around 3 T and 30 K shows a superposition of typical powder patterns of one Nb signal and at least two Al signals. 93Nb-NMR line could be reproduced by using the previously reported NQR frequency νQ ≊ 1.8MHz and asymmetry parameter η ≊ 0 [Kubo T et al 2014 JPS Conf. Proc. 3 012031]. From 27Al-NMR/NQR, NQR parameters are obtained to be ν Q,A ≊ 1.53 MHz, and ηA ≊ 0.20 for the site A, and ν Q,B ≊ 2.28 MHz, and ηB ≊ 0.17 for the site B. By comparing this result with the previous 27Al-NMR study of PrT 2Al20 (T = Ti, V) [Tokunaga Y et al 2013 Phys. Rev. B 88 085124], these two Al site are assigned to the two of three crystallographycally inequivalent Al sites.