bluuebunny/crossref_metadata_2025_split huggingface dataset:
Isolated versus Condensed Anion Structure II; the Influence of the Cations (1,3-propanediammonium, 1,4-phenylendiammonium, and n-propylammonium) on Structures and Phase Transitions of CdBr2-
4Salts A 79,81Br NQR and X-ray Structure Analysis
Authors: Ishihara Hideta , Dou Shi-qi , Horiuchi Keizo , Krishnan V. G. , Paulus Helmut , Fuess Hartmut , Weiss Alarich 
Published: February 2015

Abstract
The influence of the cations on the condensation of anions CdBr4
2- in salts (A')CdBr4 (II) and (A)2CdBr4 (II) is studied by 79,81Br NQR and X-ray crystal structure determinations. (A')CdBr4 : A' = [H3N(CH2)3NH3]2+ (1) crystallizes with a layer-type anion structure at 298 K and A' = [1,4-(H3N)2C6H4]2+ (2) crystallizes with a chain-type anion structure at 298 K. (A)2 CdBr4 : A = [n-H3C(CH2)2NH3]+ (3) crystallizes with a layer-type anion structure at 293 K. (1) shows successive phase transitions at 328, 363, and 495 K according to the NQR and DSC measurements. Phase IV of (1): at 298 K orthorhombic, Pnma, Z = 4,a = 772.1 (4), b = 1905.4(9), c = 789.8(4) pm. 81Br NQR spectrum showed a doublet at 77 K (phase IV) with ν1= 61.177 and ν2 = 45.934 MHz and also a doublet at 350 K (phase III) with ν1= 57.581 and ν2 = 48.747 MHz. (2): at 295 K orthorhombic, Pnma, Z = 4, a = 802.5(3), b = 1775.1(6), c = 881.9(3) pm; the five-coordinated Cd atom and one-dimensional [CdBr4]2- anion chain structure was observed. This coordination and chain structure are very rare for (A')CdX4 (II) or (A)2CdX4 (II). Two 81Br NQR lines were observed at 77 K: ν1= 70.159 and ν3 = 40.056 MHz. One more line appeared at 85 K: ν2 = 53.622 MHz. A 81Br NQR triplet was observed at 273 K: ν1 = 67.919, ν2 = 56.317, and ν3 = 40.907 MHz. (3) shows successive phase transitions at 121, 135, 165, and 208 K according to the NQR, DSC, and DTA measurements. Phase I of (3): at 293 K orthorhombic, Cmca, Z = 4, a = 783.4(4), b = 2480.2(10), c = 806.5(4) pm. 81Br NQR doublet was observed at 77 K (phase V) and at 300 K (Phase I) with ν1 = 61.060 and ν2 = 54.098 MHz (77 K); v1 = 55.835 and ν2 = 55.964 MHz (373 K). No NQR line could be observed in phases II, III, and IV.
A Comparison of Strategies for Obtaining High-Resolution NMR Spectra of Quadrupolar Nuclei
Authors: Youngman R. E. , Werner-Zwanziger U. , Zwanziger J. W. 
Published: February 2015

Abstract
A comparison of high-resolution NMR methods for quadrupolar nuclei is presented. The samples studied are pure and modified boron oxide glasses, and the boron NMR spectra are recorded using three different experiments capable of high resolution: Double Rotation, Dynamic Angle Spinning, and Multiple-Quantum Magic Angle Spinning. Resolution of the similar ring and nonring boron sites in these glasses, in the presence of disorder, provides a realistic study of the strengths and limitations of these experiments. Conclusions about the relative applicability of these experiments in different situations are presented.
Multidimensional NQR: Imaging and Exchange Spectroscopy
Authors: Kimmich Rainer 
Published: February 2015

Abstract
In this context a ‘‘dimension’’ can be of a spatial or of a spectroscopic nature. In the last two decades, multidimensional nuclear magnetic resonance and imaging have proven to be most useful tools for the investigation of materials. It turned out that some of these measuring principles can be applied to zero-field NQR as well. The purpose of this presentation is to elucidate two-dimensional exchange spectroscopy and imaging procedures suitable for NQR and to outline potential applications.
Enhanced Information Recovery in 2D On-and Off-Resonance Nutation NQR using the Maximum Entropy Method
Authors: Maćkowiak Mariusz , Kątowski Piotr 
Published: February 2015

Abstract
Two-dimensional zero-field nutation NQR spectroscopy has been used to determine the full quadrupolar tensor of spin - 3/2 nuclei in serveral molecular crystals containing the 3 5 Cl and 7 5 As nuclei. The problems of reconstructing 2D-nutation NQR spectra using conventional methods and the advantages of using implementation of the maximum entropy method (MEM) are analyzed. It is shown that the replacement of conventional Fourier transform by an alternative data processing by MEM in 2D NQR spectroscopy leads to sensitivity improvement, reduction of instrumental artefacts and truncation errors, shortened data acquisition times and suppression of noise, while at the same time increasing the resolution. The effects of off-resonance irradiation in nutation experiments are demonstrated both experimentally and theoretically. It is shown that off-resonance nutation spectroscopy is a useful extension of the conventional on-resonance experiments, thus facilitating the determination of asymmetry parameters in multiple spectrum. The theoretical description of the off-resonance effects in 2D nutation NQR spectroscopy is given, and general exact formulas for the asymmetry parameter are obtained. In off-resonance conditions, the resolution of the nutation NQR spectrum decreases with the spectrometer offset. However, an enhanced resolution can be achieved by using the maximum entropy method in 2D-data reconstruction.
Fast ρ-NQR Imaging with Slice Selection
Authors: Robert H. , Pusiol D. J. 
Published: February 2015

Abstract
A combination of a new pulse sequence allowing fast data acquisition in the rotating frame version of NQR (ρ-NQRI) together with a method for slice selection, is reported. The procedure allows us to record the magnetization evolution during its motion in the rotating frame. At the same time a zero-crossing external magnetic field gradient is applied in order to select a determined slice of the object to be imaged. The experiments reported are the first steps toward a fast tridimensional ρ-NQRI; even more, as the spectroscopic information is preserved during the spatial encoding procedure, it could be considered as a 3D spatially resolved NQR spectroscopy technique.
One Pulse Spin-locking in NQR
Authors: Bandyopadhyay B. , Furman G. B. , Goren S. D. , Korn C. , Shames A. L 
Published: February 2015

Abstract
The response of a quadrupolar spin system in zero applied magnetic field to a long rf pulse, for both single crystal and polycrystalline samples possessing broad Lorentzian-shaped resonance lines has been studied. The dependencies of magnetization on frequency offset, linewidth and power are investigated both theoretically and experimentally. The problem of the effective field direction in both single crystal and polycrystalline samples is also discussed. For a polycrystalline cuprous oxide (Cu2O) sample it is observed that the magnetization after a long pulse in on-resonance condition does not become zero for time t ≫ T2 , in agreement with theoretical results. It has also been shown that the magnetization increases with increase in the width of the resonance line as well as with the decrease in the excitation power.
Characterizing Phase Transitions in the Perovskites PbTiO3 and BaTiO3 Using Perturbed-Angular-Correlation Spectroscopy
Authors: Catchen Gary L. , Hollinger Edward F. , Rearick Todd M. 
Published: February 2015

Abstract
Perturbed-angular-correlation (PAC) spectroscopy was used to measure in ceramic samples of PbTiO3 and BaTiO3 the temperature dependence of the Ti-site electric-field gradients (EFGs) at temperatures very close to the ferroelectric-to-paraelectric transition temperatures Tc . The samples were doped with small amounts of Hf that carried the 181Hf - 181Ta probe radioactivity. A high-frequency nuclear quadrupole interaction that decreases very little as the temperature approaches Tc , characterizes the PbTiO3 transition. The tetragonal and cubic phases for PbTiO3 appear to coexist over a temperature interval of 8 ± 1 K, and the transition shows a thermal hysteresis of about 4 K. In contrast, a lower-frequency interaction that decreases rapidly as temperature approaches Tc , characterizes the BaTiO3, transition. Both phases of BaTiO3 appear to coexist over an interval of about 2 K, and the thermal hysteresis is about 1 K. At temperatures above Tc , both PbTiO3 and BaTiO3 show weak, non-vanishing Ti-site EFGs. Although, for BaTiO3 , this effect limits the accuracy with which critical effects can be measured, we estimate a power-law exponent ß = 0.21 ± 0.05, which most likely is somewhat lower in magnitude than the actual critical exponent. For the explanation of our observations we assume the existence of a distribution of Tc -values. This distribution would arise because the crystals could have spatially non-uniform distributions of nucleation sites, which for PbTiO3 and BaTiO3 could be point defects.
Small Scale Intramolecular Flexibility in 111mCd-Plastocyanin
Authors: Tröger W. , Lippert C. , Butz T. , Sigfridsson K. , Hansson Ö. , McLaughlin E. , Bauer R. , Danielsen E. , Hemmingsen L. , Bjerrum M. J. , Isolde  
Published: February 2015

Abstract
The effect of mutations in the vicinity of the putative electron transfer path on the metal center of the electron transfer protein plastocyanin (spinacea) is investigated by monitoring the nuclear quadrupole interaction of 111mCd in Cd-derivatives of the protein via time differential perturbed angular correlation. The spectra for the wild type protein and the mutants were rather similar. All spectra exhibit a peculiar line profile which points towards a small scale intramolecular flexibility of the metal center.
Nuclear Quadrupole Coupling Constant assignments for a series of azoles and azines by Hartree-Fock SCF-Cluster and Lattice Calculations
Authors: Palmer Michael H. 
Published: February 2015

Abstract
We present ab initio Hartree-Fock lattice calculations on a series of heterocyclic and other compounds. Some of these have previously been studied by cluster calculations with the same DZ basis sets at the SCF level. The electric field gradients at the nitrogen centres, are related to NQR experimental determinations of nuclear quadrupole coupling constants. The compounds studied include imidazole and pyrazole, 4-nitroimidazole, 4-nitropyrazole, pyrazine, and tetramethylpyrazine, pyridinium chloride, and N-methylpyridinium iodide, and pyridine-N-oxide.
The Charge Distribution in Amides and Thioamides by Nuclear Quadrupole Coupling, Dipole Moments and Electronic Structure Calculations
Authors: Palmer Michael H. , Sherwood Paul 
Published: February 2015

Abstract
The nuclear quadrupole coupling constants from microwave spectroscopy (MW) and quadrupole resonance (NQR) for amides and thioamides are discussed in relation to Hartree-Fock calculations with and without Moller-Plesset correlation effects. The view that the larger dipole moments from thioamides than the corresponding amides is a function of enhanced resonance in the former is discussed and (in effect) confirmed by the present procedures. The principal mechamism seems to be the push/pull π/σ effects of the N atom with respect to the CO and CS groups, with S being a better σ-donor than O; however, the effect is still present with formamidine where no electronegativity effects are important, so the overall effect is the 2,1,1 π-electron contribution to the allylic system from N, C, O(S). The use of localised MO’s and NO’s is described, and the centroid positions are discussed in relation to the polarity of the bonds. The LMO’s largely truncate the contributions to each NQCC to the three attached bonds (or 2 bonds + a lone pair orbital at O or S), as is used in the Townes-Dailey procedures. More distant LMO’s generally contribute < 0.05 a. u. to the EFG, simplifying the analysis. The effects of O( or S)-protonation of urea and thiourea is discussed.
Solid Effect Between Quadrupolar Transitions in Dilute Cu-Pd Alloys
Authors: Konzelmann K. , Majer G. , Seeger A. 
Published: February 2015

Abstract
The paper investigates the Dynamic Solid Effect (DSE) in Nuclear Quadrupole Double Reso-nance (NQDOR) on a system (dilute alloys of CuPd with 8, 42, 210, or 1000 at.ppm Pd) chosen for its simplicity and the possibility to test the theoretical concepts on which the experimental tech-niques (in particular the so-called Berthier-Minier technique for exhibiting the DSE) are based. NQDOR allows to observe the transitions between the Cu nuclear energy levels split by the quadrupolar interaction with the electric field gradients generated by nearby Pd atoms even in dilute alloys, in which the fraction of Cu nuclei experiencing a given field gradient is very small. The DSE permits transitions at frequencies corresponding to the sums or differences of quadrupolar level splittings at neighbouring nuclei and thus gives access to information on the spatial correlation of nuclei accessible to NQDOR studies. The DSE information is shown to be in full accord with the conclusions drawn earlier, on the basis of line-intensity arguments, on the assignment of quadrupo-lar transitions to the first four shells of Cu nuclei surrounding isolated Pd atoms but, in addition, allows to identify the low-frequency NQDOR lines associated with Cu nuclei in the fifth and sixth shells.
Electric Field Gradient Calculations of Various Borides
Authors: Schwarz K. , Ripplinger H. , Blaha P. 
Published: February 2015

Abstract
A first-principles method for the computation of electric field gradients (EFG) is illustrated for various borides. It is based on energy band calculations using the full-potential linearized aug-mented plane wave (LAPW) method within density functional theory. From the self-consistent charge density distribution the EFG is obtained without further approximations by numerically solving Poisson's equation. The dependence of the EFG on structure, chemical composition or substitution is demonstrated for the diborides MB2 (with M = Ti, V, Cr, Zr, Nb, Mo, and Ta), the hexaborides (CaB6, SrB6 and BaB6) and boron carbide which is closely related to α-boron.
Study of the EFG Trends in Zr2T (T = Fe, Co, Ni) Intermetallic Compounds
Authors: Petrilli H.M. , Marszalek M. , Saitovitch H. 
Published: February 2015

Abstract
We use the linear muffin-tin orbital formalism, in the atomic sphere approximation, to investigate the trends of the electric field gradient (EFG) at the nucleus for the non-equivalent sites in Zr2T (T = Fe, Co and Ni) intermetallic compounds. As all those compounds crystallize in the same C16 crystallographic structure, they offer a rare opportunity to investigate electronic structure effects coming from transition metals on the EFG at Zr site. Those results are compared with EFG values obtained from quadrupole coupling constant measurements performed with the time differential perturbed angular correlation (TDPAC) technique, using the 191Ta probe.
Ab initio and MNDO Calculations of the 35Cl NQR Parameters of Some Organic and Inorganic Molecules
Authors: Feshin Valentin P. , Konshin Mikhail Yu. 
Published: February 2015

Abstract
The results of ab initio and MNDO calculations of the Cl2C = CHOCH3 , XCOCl (X = CH3 , OCH3 and COCl), 4-ClC6H4CH2Cl, (CNCl)3 and PCl5 with total optimization of their geometry are presented. The ab initio calculations were executed using Hartree-Fock theory and the split valence basis set 6-31G* (RHF/6-31 G*//RHF/6-31G*). Using the calculated p-orbital populations of the CI atoms in these molecules the 35Cl NQR frequencies and asymmetry parameters of the EFG at the 35Cl nuclei have been determined. When the populations of the less diffuse components of orbitals in the split valence basis set are used the calculated and experimenal ν and η values are in good agreement. Linear correlations between these calculated and corresponding experimental ν and η values are obtained. The causes of the nonconformity of the earlier calculated ν and η values and their experimental ones are analysed.
F-Tensor Coefficients in Electric Field Gradient Calculations for Non-Coulombic Potentials
Authors: Ponnambalam M.J. 
Published: February 2015

Abstract
The F-tensor coefficients are useful in evaluating the stress-induced electric field gradients in cubic crystals. These coefficients are derived for the non-Coulombic inter-atomic potentials Gr-n and Ge-br . Interesting differences are pointed out between these results and those for Coulombic potentials.
Electric Field Gradients for Small Antimony Based Zintl Clusters from Hartree-Fock Investigations
Authors: Hagelberg F. , Das T.P. , Weil K. G. 
Published: February 2015

Abstract
Electric Field Gradient (EFG) calculations have been carried out for Antimony based clusters with 20 and with 22 valence electrons. It is shown that EFGs are very sensitive to structural changes of the clusters under study. This feature can be used to demonstrate the validity of the Zintl-Klemm-Busmann principle for these systems through EFG determinations.
Study of the Location of Implanted Fluorine Atoms in Silicon and Germanium through Their Nuclear Quadrupole Interactions
Authors: Nunes Stacie S. , Sulaiman S. , Sahoo N. , Das T. P. , Frank M. , Kreische W. , Nielsen K. B. 
Published: February 2015

Abstract
Time Differential Perturbed Angular Distribution (TDPAD) measurements of the nuclear quadrupole hyperfine parameters for 19F* implanted into amorphous, polycrystalline and crystalline silicon and germanium are reported and reviewed. Two signals are observed in the crystalline materials (≈ 35 and 23 MHz in silicon, ≈ 33 and 27 MHz in germanium) while only one is detected in the amorphous and polycrystalline samples (≈ 22 MHz in silicon, ≈ 27 in germanium). Impurity sites in these materials were modeled using a Hartree-Fock cluster procedure. The Intrabond, Antibond, and Substitutional sites in the bulk were studied in both silicon and germanium. The ATOP and Intrabond Surface sites were also studied in silicon and the results extended to germa-nium. Lattice relaxation effects were incorporated by employing a geometry optimization method to obtain minimum energy configurations for the clusters modelling each site. The electronic wave functions were obtained for each optimized cluster by applying Unresctricted Hartree-Fock theory, and these wave functions were used to calculate the nuclear quadrupole hyperfine parameters at the site of the fluorine nucleus. Comparison of the theoretical hyperfine parameters to the experimental values indicates that 19F* located in the Intrabond and Intrabond surface sites could readily explain the higher frequency signal that has been observed. 19F* in the Antibond and the surface ATOP sites yield hyperfine parameters consistent with the low frequency signal observed in the crystalline materials and the single signal observed in the amorphous (or polycrystalline) materials. Examina-tion of these two sites, in view of other available experimental evidence including the temperature dependence of the TDPAD signals, leads to the conclusion that the lower frequency signal is due to 19F* implants which have come to rest at the site of dangling bonds in the bulk. These dangling bonds are created as a result of damage generated in the individual collision cascades during the implantation process.
Theory of Nuclear Quadrupole Interactions in Solid Fluoromethanes with Implanted 19F* Nuclei. Coupling of HF* and Host Molecule
Authors: Gowri G. , Briere Tina , Srinivas Sudha , Cho Hwa-Suck , Das T.P. , Frank M. , Kreische W. , Rao K.V.S. Rama 
Published: February 2015

Abstract
The Quadrupole Coupling Constant e2qQ and Asymmetry Parameter η of fluorine for fluorine-substitute methane compounds are calculated using the Hartree-Fock Roothaan procedure. Our results are compared with experimental data from measurements by the Time Differential Perturbed Angular Distribution (TDPAD) technique using excited 19F* (spin 5/2) nuclei. The theoretical e2qQ’s for the 19F* nuclei in the fluoromethanes are in good agreement with experimental results. For CH2F2 and CHClF2 molecules, where finite η are expected from symmetry considerations, our results for η are small, 0.12 and 0.05 respectively, in agreement with experimental observation. Besides the 19F* coupling constants associated with the C-F bonds in fluoromethanes, additional interesting NQI parameters, close to those in solid hydrogen fluoride, are observed in the TDPAD measurements. It is demonstrated through investigations of the total energies and electric field gradients that these additional NQI parameters for the fluoromethanes can be explained by a HF* molecule hydrogen-bonded through the hydrogen to a fluorine atom in the host molecular systems. This complexing of an ionic molecule to the host molecules in organic solids containing strongly electronegative atoms is expected to be a general feature in both implantation and conventional techniques.
Nuclear Quadrupole Resonance in Amorphous Semiconductors
Authors: Taylor P. Craig 
Published: February 2015

Abstract
Nuclear quadrupole resonance (NQR) has provided a valuable tool for investigating the local structural order in semiconducting glasses. Measurements of NQR lineshapes and spin-lattice relaxation times help elucidate the local structural order and the unusual vibrational properties, respectively, of these glasses. In addition, NQR lineshape measurements on samples that are made under conditions that produce solids whose structures are far from equilibrium, such as fast-evap-orated films or rapidly-drawn fibers, provide detailed information on the changes in the local structural order from that which occurs in the well-annealed amorphous semiconductors.
Verification of the ‘‘Tg-Δ Rule’’ in Potassium Silicate and Sodium Tungstate Glasses
Authors: Nishida Tetsuaki 
Published: February 2015

Abstract
A linear relationship exists in oxide glasses between glass transition temperature (Tg) and quadrupole splitting (Δ) of Fe3+ . DTA and Mössbauer measurements of silicate and tungstate glasses yielded large slopes of 680 and 260 °C/(mm s-1) from the slope of the straight lines when Fe3+ occupied, as network former (NWF), distorted tetrahedral Si4+ and distorted octahedral W6+ sites, respectively. This linear relationship, named a ‘‘Tg - Δ rule’’, suggests that Tg is in proportion to the distortion of NWF-oxygen polyhedra and a higher activation energy is required for the fragments of glass to have a cooperative movement in the supercooled liquid state. The ‘‘Tg - Δ rule’’ was also valid in the case of potassium silicate glasses heat treated at the temperature close to Tg, indicating a distortion of SiO4 and FeO4 tetrahedra. Substitution of Fe3+ for individual NWF in silicate and tungstate glasses was confirmed from the Fourier transform infrared (FT-IR) spectra because only the absorption bands due to Si and W were respectively observed without the bands due to Fe.
The Bond N-Cl. (III): A 35Cl NQR and X-Ray Diffraction Study of N-Chloro-N-(2,6-Dichlorophenyl)-Acetamides
Authors: Gowda B. Thimme , Dou Shi-qi , Weiss Alarich 
Published: February 2015

(2)
The crystal structures at room temperature of the N-chloro-N-(2,6-dichlorophenyl)-chloroacetamides 2,6-Cl2C-H3 NClCOCCl3 (1) and 2,6-Cl2C6H3NClCOCH2Cl have been determined. (1): orthorhombic, Pbca. Z = 8, a = 2051.7(8) pm, b = 1134.8(4) pm, c = 1089.0(4) pm. (2): orthorhombic, Pbca, Z = S, a = 2078.7 (4) pm, b= 1487.9(4) pm, c = 694.0 (2) pm. The 35Cl NQR spectrum of (1) was studied in the range 77≤T/K≤370. At 77 K, a sextet spectrum is observed (ν in MHz): v1 = ν (Cl(N) = 56.327; ν2 = 40.636, ν3 = 40.317, ν4 = 40.294; ν5 = 36.532, ν6 = 36.182. The lines ν2, ν3, and ν4 are assigned to the CCl3 group because of their position in the frequency scale. Also, due to librational motions, this triplet part of the spectrum fades out at Tf ≈ 320 K. There is no problem in assigning in both compounds, on the basis of the known 35Cl NQR frequency scale, the line ν1 to the CI atom attached to the nitrogen atom and the lines ν5 and ν6 to the ring chlorines (Cl(2) and Cl(6)). The crystal structures and NQR spectra of (1) and (2) are discussed together with literature data for 2,6-Cl2C6H3NHCOR, C6H5NClCOR (where R = CCl3, CClH2) and other substituted acetamides.