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'Electric field gradient' in keywords Facet   Publication Year 1996  [X]
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1996[X]
1Author    DesmondC. CookRequires cookie*
 Title    Measurement of Nuclear Quadrupole Interactions using Mössbauer Spectroscopy  
 Abstract    Mössbauer spectroscopy is a useful probe for investigating nuclear quadrupole interactions. It enables the magnitude, sign and asymmetry of the electric quadrupole coupling constant to be determined. It is especially important for its ability to measure these parameters for excited nuclear states. The Mössbauer effect is used to measure excited state quadrupole moments in materials whose electric field gradient (EFG) is known. More commonly however, it is used to determine the EFG from which atomic bonding and electronic structure are determined. The technique also allows temperature dependent orientation of sublattice magnetization to be measured using the direction of the electric quadrupole coupling as a reference. 
  Reference    Z. Naturforsch. 51a, 368—372 (1996); received November 20 1995 
  Published    1996 
  Keywords    Mössbauer Effect, Electric Field Gradient, Quadrupole Interaction 
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 TEI-XML for    default:Reihe_A/51/ZNA-1996-51a-0368.pdf 
 Identifier    ZNA-1996-51a-0368 
 Volume    51 
2Author    StadeS. Nunes, S. Sulaiman, N. Sahoo, T. P. Das, M. Frank, W. Kreische, K. B. NielsenRequires cookie*
 Title    Study of the Location of Implanted Fluorine Atoms in Silicon and Germanium through Their Nuclear Quadrupole Interactions  
 Abstract    Time Differential Perturbed Angular Distribution (TDPAD) measurements of the nuclear quadrupole hyperfine parameters for 19 F* implanted into amorphous, polycrystalline and crys-talline 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 (ä22 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 19 F* located in the Intrabond and Intrabond surface sites could readily explain the higher frequency signal that has been observed. 19 F* 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 19 F* 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. 
  Reference    Z. Naturforsch. 51a, 560—564 (1996); received December 12 1995 
  Published    1996 
  Keywords    Semiconductors, Impurities, Electronic structure, Hartree-Fock, Electric field gradient 
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 TEI-XML for    default:Reihe_A/51/ZNA-1996-51a-0560.pdf 
 Identifier    ZNA-1996-51a-0560 
 Volume    51 
3Author    P. Wodniecki, B. Wodniecka, M. Marszalek, A. Z. HrynkiewiczRequires cookie*
 Title    PAC Studies of Ag-Hf Intermetallic Compounds  
 Abstract    The hyperfine quadrupole interaction of 181 Ta and 111 Cd probes in HfAg and HfiAg com-pounds was studied at 24 to 1100 K with the time -differential perturbed angular correlation (TDPAC) technique. The EFGs measured in HfAg on 181 Ta and m Cd are 1.388(5)x 10 18 VcnT 2 and 0.340(5)x 10 lx Vcm -2 , respectively. For both probe atoms a linear decrease of the EFG with temperature was observed with slopes 1.1 l(2)x 10 -4 KT 1 and 1.73(5)x 10~ 4 KT 1 for 181 Ta and "'Cd, respectively. In Hf 2 Ag, 0.469(2)x 10 18 VcnT 2 was determined on 181 Ta nuclei and 0.428(5)x 10 18 Vcm -2 on '"Cd. Also a linear EFG temperature dependence with the large slope of 2.39(6)x 10 -4 K" 1 was observed for "'Cd probes in Hf 2 Ag, while the EFG measured on l8l Ta nuclei in this compound exhibits a very weak temperature variation which can be fitted neither with a linear T nor a T ?/2 dependence. In all cases the electronic contributions to the EFG are very small indicating that these transition element systems do not obey the universal correlation between the electronic and the ionic EFG observed in numerous other systems not belonging to the transition metal series. 
  Reference    Z. Naturforsch. 51a, 437—441 (1996); received November 20 1995 
  Published    1996 
  Keywords    Hyperfine interactions, perturbed angular correlations, electric field gradient, inter-metallic compounds, Ag-Hf system 
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 TEI-XML for    default:Reihe_A/51/ZNA-1996-51a-0437.pdf 
 Identifier    ZNA-1996-51a-0437 
 Volume    51 
4Author    K. Konzelmann, G. Majer, A. SeegerRequires cookie*
 Title    Solid Effect Between Quadrupolar Transitions in Dilute Cu-Pd Alloys  
 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. 
  Reference    Z. Naturforsch. 51a, 506—514 (1996); received February 13 1996 
  Published    1996 
  Keywords    Nuclear quadrupole double resonance, Atomic defects in Cu, Electric field gradients, Solid effect 
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 TEI-XML for    default:Reihe_A/51/ZNA-1996-51a-0506.pdf 
 Identifier    ZNA-1996-51a-0506 
 Volume    51 
5Author    H. M. Petrilli, M. Marszalek, H. SaitovitchRequires cookie*
 Title    Study of the EFG Trends in Zr 2 T (T = Fe, Co, Ni) Intermetallic Compounds  
 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 Zr 2 T (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 181 Ta probe. 
  Reference    Z. Naturforsch. 51a, 537—543 (1996); received February 13 1996 
  Published    1996 
  Keywords    Electric Field Gradient, Intermetallic Compounds, LMTO-ASA, Electronic Structure, Nuclear Quadrupole Interactions 
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 TEI-XML for    default:Reihe_A/51/ZNA-1996-51a-0537.pdf 
 Identifier    ZNA-1996-51a-0537 
 Volume    51 
6Author    F. Hagelberg, T. P. Das, K. G. WeilRequires cookie*
 Title    Electric Field Gradients for Small Antimony Based Zintl Clusters from Hartree-Fock Investigations  
 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. 
  Reference    Z. Naturforsch. 51a, 557—559 (1996); received February 3 1996 
  Published    1996 
  Keywords    Ab Initio Theory, Atomic Clusters, Antimony Molecules, Electric Field Gradients, Zintl Clusters 
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 TEI-XML for    default:Reihe_A/51/ZNA-1996-51a-0557.pdf 
 Identifier    ZNA-1996-51a-0557 
 Volume    51 
7Author    H. Honda, M. Kenmotsu, N. Onoda-Yamamuro, H. Ohki, S. Ishimaru, R. Ikeda, Y. FurukawaRequires cookie*
 Title    N and 133 Cs Solid NMR Studies on Ionic Dynamics in Plastic CsN0 2  
 Abstract    The temperature dependence of the 15 N and 133 Cs NMR spin-lattice relaxation times, the 15 N spin-spin relaxation time, and the 1S N and 133 Cs spectra of CsNOi was observed in the plastic phase (209.2 < T < 673 K (m. p.)) and the low-temperature phase (Phase II). In Phase II we found the N07 180°-flip, which could be attributed to the anomalous increase of the heat capacity curve, and determined the activation energy of this motion to be 8.7-11.7 kJ mol -1 . The l5 N and 133 Cs spectra in this phase are inconsistent with the reported crystal structure R3m and can be explained by lower crystal symmetry. In the plastic phase we detected a new anionic motion with 11 kJ mol -1 , an isotropic N07 reorientation with 8.5-9 kJ mol -1 , and ionic self-diffusion with 47 kJ mol . The presence of ionic self-diffusion was confirmed by measuring the electrical conductivity. 
  Reference    Z. Naturforsch. 51a, 761—768 (1996); received October 24 1995 
  Published    1996 
  Keywords    |S N and 133 Cs Solid NMR, Plastic crystal Phase transition Chemical shift anisotropy, Electric field gradient 
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 TEI-XML for    default:Reihe_A/51/ZNA-1996-51a-0761.pdf 
 Identifier    ZNA-1996-51a-0761 
 Volume    51