scholarly journals Theoretical Studies of the Electric Field Gradient in Hexachlorometallates

1988 ◽  
Vol 43 (7) ◽  
pp. 643-650 ◽  
Author(s):  
Dirk Borchers ◽  
Peter C. Schmidt ◽  
Alarich Weiss
Keyword(s):  
Electric Field ◽  
Electric Field Gradient ◽  
Field Gradient ◽  
Central Atom ◽  
Coupling Constants ◽  
Point Charge Model ◽  
Metal Atoms ◽  
Charge Model ◽  
Quadrupole Coupling ◽  
Distorted Octahedra

Abstract The electric field gradient (EFG) at the chlorine site is calculated for cubic compounds of the K2PtCl6-type (space group Fm3m), M2IMIVCl6, where M1 is an alkali metal and MeIV a tetravalent element. In the calculations the total EFG is subdivided into the contribution of the complex [MIVCl6]2-, EFGcomplex, and the contribution of the ions outside the complex, EFGlattice. EFGcomplex is calculated by the local electron density formalism using the MS-Xα-method, and EFGlattice is determined by the point charge model.It is found that EFGcomplex is positive whereas EFGlattice is negative. Including antishielding effects, the magnitude of EFGlattice is about one fourth of EFGcomplex. The trends in the EFG for the various compounds found theoretically are the same as the trends in the experimental nuclear quadrupole coupling constants e2Q q/h. However, the absolute values of EFGtheo are smaller than the values EFGexp deduced from e2Q q/h.For a fixed central atom MIV the (positive) EFGexp is increasing with increasing radii of the cations (and increasing lattice constant). This increase can be understood by an increase of EFGlattice.On the other hand, for fixed cations and different tetravalent metal atoms, the EFG is increasing with increasing electronegativity of the central atom. This can be understood by an increase of EFGcomplex. For distorted octahedra it is found that the change in the EFG due to the distortion is also due to a change in EFGcomplex.

The Electric Field Gradient at the Site of the Halogen Ion and Structure of Amino Acid Hydrobromides and Hydroiodides

1992 ◽  
Vol 47 (7-8) ◽  
pp. 887-917
Author(s):  
Armin Kehrer ◽  
Shi-qi Dou ◽  
Alarieh Weiss
Keyword(s):  
Electric Field ◽  
Electric Field Gradient ◽  
Field Gradient ◽  
Room Temperature ◽  
Low Frequency ◽  
Coupling Constants ◽  
Coupling Constant ◽  
Resonance Frequencies ◽  
Quadrupole Coupling ◽  
Frequency Coupling

Abstract The 79,81Br and 127I NQR spectra of several hydrobromides, respectively hydroiodides, of amino acides and dipeptides were studied, mostly as functions of temperature in the range 77 < T/K <420. The investigated compounds are: L-Arg • HBr • H2O, L-Cys • HBr • H2O , L - Cys - S - S - L - Cys • 2HBr, ethanolamine • HBr, L-Glu • HBr, L-His • HBr, L-His • 2HBr, L-Ile HBr • H2O , Sar • HBr, (Sar)2 • HBr, L-Val • HBr • H2O , Gly • LiBr, Gly-Gly • LiBr, ethanolamine HI, Sar • HI, (Sar)2 • HI, (Gly)2 • HI, (L-Val)2 • HI, Gly-L-Leu • HI • H2O . A phase transition with hysteresis was observed for L-Val • HBr • H2O (Tc.up = 318 K, Tc.down = 242 K). Two solid phases of Sar • HI have been studied by NQR, one crystallized from melt, the other one from aqueous solution. For three of the title compounds the crystal structure was determined at room temperature: L-His - 2HBr, P212121 , Z = 4, aj pm = 1652, b/pm = 916, c/pm = 721; L-Cys HBr H2O , P212121 , Z = 4, a/pm = 1955, b/pm = 746, c/pm = 550; Gly-L-Leu • HI • H2O , P2X, Z = 2, a / p m = 1289, b/pm = 914, c/pm = 615, ß/° = 99.In most cases the halogen ion in the studied hydrohalides is polycoordinated by hydrogen bonds of the type N - H • • • X⊖ and O - H • • • X⊖ , X = Br, I. The NQR frequencies and, for iodine, the nuclear quadrupole coupling constants depend on this coordination. A low frequency (coupling constant) region is found for pure N - H • • • X⊖ coordination. Replacing one N - H • • • X⊖ bond by O - H • • • X⊖ rises the electric field gradient, EFG, respectively the resonance frequencies. The dependence of the EFG on the hydrogen bond coordination N - H • • • X⊖ plus O - H • • • X⊖ is discussed for the title compounds including information from literature

Assignment and structural dependence of electric field gradients in anorthite and simple field gradient calculations in some aluminosilicates

1974 ◽  
Vol 140 (5-6) ◽  
Author(s):  
J. L. Staehli ◽  
D. Brinkmann
Keyword(s):  
Electric Field ◽  
Field Gradient ◽  
Quadrupole Coupling Constant ◽  
Coupling Constant ◽  
Electric Field Gradients ◽  
Point Charge Model ◽  
Polarization Effects ◽  
Field Gradients ◽  
Charge Model ◽  
Quadrupole Coupling

AbstractThe electric field gradient tensors at theIt was found that the quadrupole coupling constant is correlated with the distortion of the coordination tetrahedra and that the simple point-charge model which neglects polarization effects is apt to yield quite satisfying results for very distorted tetrahedra.Similar results were obtained for the Al and Na sites in albite, NaAlSi

Electric Field Gradient Modulation in Incommensurate Systems X2YZ4

1986 ◽  
Vol 41 (1-2) ◽  
pp. 256-260
Author(s):  
J. Pirnat ◽  
J. Lužnik ◽  
Z. Trontelj
Keyword(s):  
Electric Field ◽  
Electric Field Gradient ◽  
Field Gradient ◽  
Point Charge ◽  
Reasonable Agreement ◽  
Point Charge Model ◽  
Resonant Nucleus ◽  
Charge Model ◽  
The Subject ◽  
Wave Limit

The subject of the paper is the plane wave limit of static incommensurate displacement modulation in the crystal structure, which is related to the commensurate ferrophase modulation. Using the point charge model, the corresponding electric field gradient modulation and quadrupole perturbed NMR spectra are calculated. The corrections up to the 4th order owing to the incoherent displacements of the charges in the vicinity of the resonant nucleus are considered. Comparison with the experimental data shows a reasonable agreement.

scholarly journals Theoretical Study of the Electric Field Gradient in Silver Iodide

1992 ◽  
Vol 47 (1-2) ◽  
pp. 182-188
Author(s):  
G. Frantz ◽  
R. Leiberich ◽  
P. C. Schmidt
Keyword(s):  
Band Structure ◽  
Electric Field ◽  
Electric Field Gradient ◽  
Field Gradient ◽  
Point Charge ◽  
Cluster Approach ◽  
Point Charge Model ◽  
Hartree Fock ◽  
Charge Model ◽  
Theoretical Results

AbstractThe electric field gradient (EFG) in hexagonal Agl at the iodine site is studied theoretically by three different procedures, namely the point charge model, the Hartree-Fock cluster approach, and the augmented plane wave band structure procedure. A comparison is made for the electronic charge distribution and the sizes of the various contributions to the EFG obtained by the different procedures. From the point charge model and the Hartree-Fock cluster approach one gets almost the same result for the EFG, q = +0.743 • 1021 V/m2 and +0.816 • 1021 V/m2 respectively. Only a rather preliminary result of q = +0.393 • 1021 V/m2 is found by the band structure calculation to be compared with the experimental value of qexp= ±0.415 • 1021 V/m2 . The confidence limits of the theoretical results are discussed, including possible ways to bridge the gap between the theoretical results by different methods and experiment. Both the cluster and the band structure calculations are shown to support an ionic model for hexagonal Agl with some overlap between the charge distributions on neighboring ions.

Electric field gradient at Cu nucleaus in CuO: single-crystal NMR determination and point charge model

1991 ◽  
Vol 181 (1-3) ◽  
pp. 121-126 ◽  
Author(s):  
L. Cristofolini ◽  
G. Amoretti ◽  
C. Bucci ◽  
P. Carretta ◽  
R. De Renzi ◽  
...  
Keyword(s):  
Electric Field ◽  
Single Crystal ◽  
Electric Field Gradient ◽  
Field Gradient ◽  
Point Charge ◽  
Point Charge Model ◽  
Charge Model

Notizen: Non-empirical Calculation of Quadrupole Coupling Constants in the Hydrogen Bonded System D(OH2)2+

1974 ◽  
Vol 29 (8) ◽  
pp. 1231-1232
Author(s):  
J. Koller ◽  
A. Ažman
Keyword(s):  
Electric Field ◽  
Electric Field Gradient ◽  
Field Gradient ◽  
Coupling Constants ◽  
Interatomic Distances ◽  
Quadrupole Coupling ◽  
Hydrogen Bonded

The electric field gradient at the hydrogen bonded deuteron in D(OH2)2+ is calculated. The results do not indicate relations between the quadrupole coupling constants and the OD or OO interatomic distances.

NUCLEAR ELECTRIC QUADRUPOLE INTERACTION IN SINGLE CRYSTALS

1952 ◽  
Vol 30 (3) ◽  
pp. 270-289 ◽  
Author(s):  
G. M. Volkoff ◽  
H. E. Petch ◽  
D. W. L. Smellie
Keyword(s):  
Electric Field ◽  
Electric Field Gradient ◽  
Field Gradient ◽  
Electric Quadrupole ◽  
Quadrupole Coupling Constant ◽  
Coupling Constant ◽  
Gradient Tensor ◽  
Absolute Value ◽  
Principal Axes ◽  
Quadrupole Coupling

Pound's theory of the dependence of electric quadrupole splitting of nuclear magnetic resonance absorption lines in a single crystal on the orientation of the crystal in an external magnetic field is extended to cover the case of a crystal with nonaxially symmetric electric field gradient at the site of the nuclei being investigated. It is shown that an experimental study of the angular dependence of this splitting for three independent rotations of the crystal about any three mutually perpendicular axes will yield complete information about the orientation of the principal axes and the degree of axial asymmetry of the electric field gradient tensor at the site of the nuclei, and also will give the absolute value of the quadrupole coupling constant for those nuclei.The authors' experiments on the splitting of the Li7 absorption lines in a single crystal of LiAl(SiO3)2 (spodumene) are described and are used to illustrate the theory. The absolute value of the quadrupole coupling constant for the Li7 nuclei in spodumene is found to be [Formula: see text]. per sec. The axial asymmetry parameter of the field gradient tensor at the site of the Li nuclei is found to be η≡(ϕxx−ϕvv)ϕzz=0.79 ± 0.01. One of the principal axes of this tensor (the y axis corresponding to the eigenvalue of intermediate magnitude) is experimentally found to coincide with the b crystallographic axis of monoclinic spodumene as required by the known symmetry of the crystal. The other two principal axes are in the ac plane, the z axis (corresponding to the eigenvalue ϕzz of greatest magnitude) lying between the a and c axes at an angle of 48° ± 2° with the c axis.

Determination of electric field gradient parameters in tellurium

1976 ◽  
Vol 54 (16) ◽  
pp. 1692-1698 ◽  
Author(s):  
K. Hamilton ◽  
B. M. Powell ◽  
P. Martel
Keyword(s):  
Electric Field ◽  
Electric Field Gradient ◽  
Field Gradient ◽  
Inelastic Neutron Scattering ◽  
Mean Square Displacement ◽  
Inelastic Neutron ◽  
Charge Model ◽  
Bond Charge ◽  
Bond Charge Model

The relative intensities of the Mössbauer doublet in Te have been analysed at 4 K and 80 K by utilizing values of the mean square displacement tensor derived from inelastic neutron scattering measurements. The orientation β of the electric field gradient ellipsoid and its asymmetry parameter η have been determined. At 4 K, β = 90°, η = −0.17 and at 80 K, β = 92°, η = −0.48. A simple 'bond charge' model is proposed in an attempt to understand the discrepancy between these values of the electric field gradient parameters and those obtained theoretically by other authors.

scholarly journals Response of the Electric Field Gradient in Ion implanted BaTiO3 to an External Electric Field

2000 ◽  
Vol 655 ◽  
Author(s):  
Marc Dietrich ◽  
Jörn Bartels ◽  
Manfred Deicher ◽  
Kristian Freitag ◽  
Vyacheslav Samokhvalov ◽  
...  
Keyword(s):  
Electric Field ◽  
Electric Field Gradient ◽  
Field Gradient ◽  
External Electric Field ◽  
Correlation Spectroscopy ◽  
Quadratic Term ◽  
Linear Change ◽  
Model Calculations ◽  
Charge Model ◽  
Piezoelectric Constants

AbstractSingle crystalline, ferroelectric BaTiO3 as material with the highest piezoelectric constants among the perovskites with ordered sublattices was implanted with 111In(111Cd). The electric field gradient at the Ti position was measured with perturbed γγ-angular correlation spectroscopy (PAC) while the crystal was exposed to an external electric field. A quadratic dependence could be observed: νQ(E) = (34.8(1) + 0.16(4) E/kV/mm + 0.080(2) E2/kV2/mm2) MHz. Point charge model calculations reproduce the linear change of Vzz, but not the quadratic term. The polarizability of the host ions of BaTiO3 is known to be nonlinear with respect to an electric field. The resulting quadratic shift of the electron density is reflected in the strength of the EFG.

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