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1998[X]
1Author    PhilipJ. Bray, GaryL. PetersenRequires cookie*
 Title    NMR and NQR Studies of Borate Glasses  
 Abstract    Nuclear magnetic resonance (NMR) has been used for some 40 years to study atomic arrange-ments, chemical bonding, and structural groupings in borate glasses and crystalline compounds, and nuclear quadrupole resonance (NQR) has more recently increased the resolution and accuracy of the measurements. Examples are presented of the use of first-order and second-order quadrupo-lar effects in "B NMR spectra to obtain structural information, and n B and 10 B NQR spectra to obtain the quadrupolar parameters Q cc (the coupling constant) and 77 (the asymmetry parameter) with accuracies of 5 or 6 significant figures, and 3 figures, respectively. Q cc and 77 are extremely sensitive to changes in atomic rearrangements and chemical bonds, so they are excellent monitors and provide identification of bonding configurations and structural groupings in borates: Examples are also presented in which combinations of NMR and NQR data are used to extract the desired information. NQR detection of resonances at frequencies as low as 276 kHz is discussed. 
  Reference    Z. Naturforsch. 53a, 273—284 (1998); received December 30 1997 
  Published    1998 
  Keywords    NMR, NQR, Borates, Quadrupolar Interactions 
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 TEI-XML for    default:Reihe_A/53/ZNA-1998-53a-0273.pdf 
 Identifier    ZNA-1998-53a-0273 
 Volume    53 
2Author    Maria Zdanowska-Fnjczek, Malgorzata Grottel, Ryszard JakubasRequires cookie*
 Title    C1 NQR and l H NMR Studies of Molecular Motions in Guanidinium Salt of Chloroacetic Acid  
 Abstract    Multinuclear NQR and NMR techniques have been applied in order to study the molecular dynamics in [C(NH 2) 3 ](ClH 2 CCOO). The 35 C1 NQR frequency was measured over a wide range of temperature. The experimental results were described by using the theories of Bayer and Brown which take into account the torsional oscillations of the CClH 2 -group of the anion. A study of the proton NMR second moment as well as relaxation times T, and T Xp performed in a wide temperature range revealed an onset of the guanidinium cation reorientation around its two-fold symmetry axis. Activation parameters for this motion were determined. 
  Reference    Z. Naturforsch. 53a, 484—487 (1998); received March 24 1998 
  Published    1998 
  Keywords    NMR, NQR, Molecular Motion 
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 TEI-XML for    default:Reihe_A/53/ZNA-1998-53a-0484.pdf 
 Identifier    ZNA-1998-53a-0484 
 Volume    53 
3Author    Tetsuo Asaji, Keizo Horiuchi, Takehiko Chiba, Takashige Shimizu, Ryuichi IkedaRequires cookie*
 Title    NMR * NQR and DTA * DSC Studies of Phase Transitions in Pyridinium Tetrachloropalladate(II) and Pyridinium Tetrachloroplatinate(II)  
 Abstract    From the measurements of DTA • DSC and the temperature dependences of 35 C1 NQR frequen-cies, phase transitions were detected at 150 K, 168 K, and 172 K for (pyH) 2 [PtCl 4 ], and at 241 K for (P yH) 2 [PdCl 4 ], In order to elucidate the motional state of the constituent ions in the crystals in connec-tion with the structural phase transitions, the 35 C1 NQR and 'H NMR spin-lattice relaxation times and the second moment of the 'H NMR line were measured as functions of temperature. For both com-pounds, the potential wells for the cationic reorientation are suggested to be highly nonequivalent at low temperatures. Above 168 K, the pyridinium ions in (pyH) 2 [PtCl 4 ] are expected to reorient between almost equivalent potential wells. As for (pyH) 2 [PdCl 4 j, it is expected that the orientational order of the cation still remains even above the second order transition at 241 K. A change of the potential curve from two-unequal to three-unequal wells is proposed as a possible mechanism of the second order tran-sition. The activation energies for the cationic motion in the respective model potential are derived for both compounds at high and low temperatures. 
  Reference    Z. Naturforsch. 53a, 419—426 (1998); received December 30 1997 
  Published    1998 
  Keywords    Phase transition, NQR, NMR, Spin-lattice relaxation, DSC 
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 TEI-XML for    default:Reihe_A/53/ZNA-1998-53a-0419.pdf 
 Identifier    ZNA-1998-53a-0419 
 Volume    53 
4Author    Lucia Calucci, Claudia Forte, Marco Geppi, CarloAlberto VeraciniRequires cookie*
 Title    Dynamics of Liquid Crystals by Means of 2 H-NMR: a Comparison between 4,4'-bis(hexyloxy)azoxybenzene and the Derivative Pd(II) Complex AZPAC  
 Abstract    In the present work we report a molecular dynamics investigation of the two mesogens 4,4'-bis(hexyloxy)azoxybenzene (HL) and its Pd(II) acetylacetonate derivative Azpac in their nematic phases. Deuterium Zeeman and quadrupolar spin-lattice relaxation times have been measured at 46.04 MHz on two isotopomers of Azpac (Azpac-d 4 and Azpac-c/ 26 > deuteriated on the aromatic core and on the alkoxy chains, respectively) and on HL-d 4 , an isotopomer of HL partially deuteri-ated on the aromatic core, by means of the Wimperis pulse sequence. The spectral densities obtained from the measured relaxation times are discussed in terms of internal and overall molecular motions. A small step rotational diffusion model for the overall molecular motions, superimposed on a free rotational model for internal motions, allowed diffusion coefficients for molecular spinning and tumbling and for phenyl ring rotations to be derived for HL; the same models were used in describing the dynamics of Azpac. 
  Reference    Z. Naturforsch. 53a, 427—435 (1998); received October 31 1997 
  Published    1998 
  Keywords    Liquid Crystals, Deuterium Relaxation, Molecular Dynamics, Metallomesogens, NMR 
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 TEI-XML for    default:Reihe_A/53/ZNA-1998-53a-0427.pdf 
 Identifier    ZNA-1998-53a-0427 
 Volume    53 
5Author    Detlef BrinkmannRequires cookie*
 Title    Spin Gap, Electronic Crossover, and Charge Density Waves in Y-Ba-Cu-O Superconductors  
 Abstract    This paper discusses recent NQR/NMR studies performed on Y-Ba-Cu-0 superconductors at the Uni-versity of Zürich. The work is concerned with normal state properties which are still controversial, for instance the spin-gap effect, i.e. the opening of a pseudo gap in the electron spin excitation spectrum at a temperature 7*, which lies above T c . We will report on the detection of "anomalies" which are dis-played in the temperature dependence of several NMR and NQR quantities measured in the normal state of YBa 2 Cu 4 0 8 . These anomalies are interpreted as an electronic crossover which involves a charge re-distribution in the Cu0 2 planes and an enhancement of the charge fluctuations. As a possible mecha-nism of the crossover, a charge density wave instability is proposed. 
  Reference    Z. Naturforsch. 53a, 488—491 (1998); received December 30 1997 
  Published    1998 
  Keywords    NQR, NMR, High-Temperature Superconductors, Spin gap Electronic Crossover 
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 TEI-XML for    default:Reihe_A/53/ZNA-1998-53a-0488.pdf 
 Identifier    ZNA-1998-53a-0488 
 Volume    53 
6Author    H. Nishihara, T. Kanomata, K. Sato, N. Suzuki, T. HaradaRequires cookie*
 Title    NMR of 51 V in VRuP: Possible Onset of Charge-Density-Waves  
 Abstract    NMR experiments are reported for VRuP which has an orthorhombic TiNiSi structure and shows anomalies in the temperature dependence of the electric conductivity and static susceptibility. A field-swept spectrum of 5 'V perturbed by a quadrupole interaction has been observed, which shows no anomalous temperature dependence. However, the metallic spin-lattice relaxation rate decreases in a stepwise fashion with decreasing temperature at around 200 K, in accordance with the resistivity and the susceptibility data, suggesting a possible CDW formation in this material. 
  Reference    Z. Naturforsch. 53a, 524—527 (1998); received January 26 1998 
  Published    1998 
  Keywords    NMR, CDW, VRuP, 51 V, Spin-Lattice Relaxation 
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 TEI-XML for    default:Reihe_A/53/ZNA-1998-53a-0524.pdf 
 Identifier    ZNA-1998-53a-0524 
 Volume    53 
7Author    Shin'. Ichi Ishimaru, Miho Yamauchi, Ryuichi IkedaRequires cookie*
 Title    Dynamics of Interlayer Cations in Tetramethylammonium-Saponite Studied by l H, 2 H NMR, and Electrical Conductivity Measurements  
 Abstract    We observed 'H and 2 H NMR spectra, 'H NMR spin-lattice relaxation times, and electrical con-ductivities of water-saturated and anhydrous tetramethylammonium(TMA)-saponites between 100 and 415 K. The very weakly bound cations produced narrow *H and 2 H NMR lines observed in both specimens down to 150 K. The temperature dependence of the 'H NMR spin-lattice relaxation times in the water-saturated and anhydrous samples gave asymmetric minima attributable to the heteroge-neous overall rotation and self-diffusion of the cations. The inhomogeneity of the cationic motions in the anhydrous TMA-saponite was greater than in the water-saturated one. From measurements of the electrical conductivity of anhydrous TMA-saponite a large anisotropic cation-diffusivity was concluded. 
  Reference    Z. Naturforsch. 53a, 903—908 (1998); received June 2 1998 
  Published    1998 
  Keywords    Saponite, Cation Dynamics, NMR, Electrical Conductivity, Intercalation 
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 TEI-XML for    default:Reihe_A/53/ZNA-1998-53a-0903.pdf 
 Identifier    ZNA-1998-53a-0903 
 Volume    53 
8Author    H. Yoshida, H. Nishihara, S. Yokota, M. Ohyanagi, T. NakaokiRequires cookie*
 Title    Field-Swept NMR Spectra of n B in Pyrex Glass and 93 Nb in NbN Perturbed by Quadrupole Interaction  
 Abstract    NMR experiments of "B by both field-swept and high-resolution NMR are reported to probe the electric field gradient at boron sites and its distribution in Pyrex glass. Both spectra are successfully interpreted with the same set of parameters. It is stressed that field-swept NMR experiments to observe total powder spectrum can be helpful to get information on electric field gradients and asymmetry pa-rameters if there exist many nonequivalent sites of atoms, since satellite transitions are affected by the larger first-order quadrupole effect. Field-swept NMR of 93 Nb in superconducting NbN powder, pre-pared by self-propagating high-temperature synthesis, is also reported. A very broad field-swept spec-trum disturbed by quadrupole interaction has been observed. The spectrum is simulated by assuming distributions in electric field gradient and Knight shift at Nb sites. It is stressed that a combination of experiments at separated frequencies is important 
  Reference    Z. Naturforsch. 53a, 309—313 (1998); received January 26 1998 
  Published    1998 
  Keywords    NMR, Pyrex, Glass, n B, NbN, Superconductor, 93 Nb 
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 TEI-XML for    default:Reihe_A/53/ZNA-1998-53a-0309.pdf 
 Identifier    ZNA-1998-53a-0309 
 Volume    53 
9Author    Yasumasa Tomita, Koji Yamada, Hiroshi Ohki, Tsutomu OkudaRequires cookie*
 Title    Structure and Dynamics of Li 3 InBr 6 and NaInBr 4 by Means of Nuclear Magnetic Resonance  
 Abstract    Li 3 InBr 6 and NaInBr 4 have been synthesized and characterized by means of DTA, 8 'Br NQR, 6 Li, 7 Li, 23 Na, and ll5 In NMR, and AC conductivity. These measurements revealed the presence of phase transitions and cationic diffusion in both compounds. From the spin-lattice relaxation times of 1 Br NQR and the peak widths of 7 Li and 23 Na NMR spectra, it is deduced that the conduction is due to cat-ionic diffusion. The activity energy for the Li + diffusion was found to be 24 kJ/mol for Li 3 InBr 6 . 
  Reference    Z. Naturforsch. 53a, 466—472 (1998); received January 26 1998 
  Published    1998 
  Keywords    NQR, NMR, Spin-lattice Relaxation Time, AC Conductivity, Cation Diffusion 
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 TEI-XML for    default:Reihe_A/53/ZNA-1998-53a-0466.pdf 
 Identifier    ZNA-1998-53a-0466 
 Volume    53 
10Author    C. Cruz, P. J. Sebastião, J. Figueirinhas, A. C. Ribeiro, H. T. Nguyen, C. Destrade, F. NoackRequires cookie*
 Title    NMR Study of Molecular Dynamics in a D ho Columnar Mesophase  
 Abstract    In this paper we report the first molecular dynamics study combining fast field-cycling and conven-tional NMR techniques in a thermotropic liquid crystal of discotic molecules exhibiting an ordered columnar hexagonal mesophase. Using the association of these techniques we obtained proton T { data over a very large domain of Larmor frequencies (u/2n from 500 Hz to 85 MHz). The proton spin-lattice relaxation results were analysed considering the structure of the mesophase and the types of movements which are expected to influence significantly the relaxation rate, namely local molecu-lar rotational reorientations, inter-columnar self-diffusion and collective movements corresponding to bending and compression of the columns. We verified that these mechanisms dominate the relaxation respectively for high, medium and low Larmor frequencies. 
  Reference    Z. Naturforsch. 53a, 823—827 (1998); received July 16 1998 
  Published    1998 
  Keywords    NMR, Proton Relaxation, Molecular Dynamics, Columnar Hexagonal Mesophases (D ho ), Discotic Molecules 
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 TEI-XML for    default:Reihe_A/53/ZNA-1998-53a-0823.pdf 
 Identifier    ZNA-1998-53a-0823 
 Volume    53