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61Author    Masao Hashimoto, Shinichi Hashimoto, Hiromitsu Terao, Masayuki Kuma, Haruo Niki, Hiroyuki InoRequires cookie*
 Title    Crystal Structure and Phase Transition of 4-Aminopyridinium Tetrabromoantimonate(III) as Studied by Bromine and Antimony NQR, Proton NMR, and Single Crystal X-Ray Diffraction  
 Abstract    The crystal structure of the room temperature phase (RTP) of the title compound was determined at 297 K (monoclinic, space group C2/c, a = 1384.2(2), b = 1377.8(3), c = 755.5(2) pm, ß = 121.58(1)°). A complicated disorder was found for the cation. A phase transition from the low-temperature phase (LTP) to the RTP was found at (224 ±1) K (T c). The 'H NMR spectra showed a sharp motional narrowing at ca. T=T C , indicating the occurrence of a reorientational motion of the cation in the RTP in accord with the disorder. It was found that another reorientational motion is excited in the LTP. Four 81 Br NQR lines (132.71, 115.38, 61.54 and 59.31 MHz at 77 K) and two Sb NQR lines (53.78 and 33.76 MHz at 77 K) were found in the LTP, while a single 81 Br NQR line was observed at T> 276 K (ca. 121.80 MHz at 300 K). Crystal dynamics are discussed on the basis of the temperature dependence of the NQR, *H NMR line width, and 'H NMR Tj. 
  Reference    Z. Naturforsch. 55a, 167—172 (2000); received August 24 1999 
  Published    2000 
  Keywords    4-NH 2 PyHSbBr 4, Crystal Structure, Phase Transition, NQR, 'H NMR 
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 TEI-XML for    default:Reihe_A/55/ZNA-2000-55a-0167.pdf 
 Identifier    ZNA-2000-55a-0167 
 Volume    55 
62Author    J. Pirnat, Z. Trontelj, J. Lužnik, D. KirinRequires cookie*
 Title    Halogen NQR and the Phase Transition in CH 3 Hg-Halide Family  
 Abstract    The temperature dependence of the 35 C1 NQR line and its relaxation has been measured from 77 K to room temperature. The known displacive phase transition near 162 K is reflected in the change of the slope of the temperature dependence of the quadrupole line, but not so in the chlorine or proton relaxation. The results are discussed in view of the proposed structural changes and thermal vibrations. 
  Reference    Z. Naturforsch. 55a, 215—218 (2000); received October 13 1999 
  Published    2000 
  Keywords    Methylmercury Chloride, NQR, Crystal Structure, Phase Transition, Thermal Vibrations 
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 TEI-XML for    default:Reihe_A/55/ZNA-2000-55a-0215.pdf 
 Identifier    ZNA-2000-55a-0215 
 Volume    55 
63Author    J. Roth, M. Uhrmacher, R. De, La Presa, L. Ziegeler, K. P. LiebRequires cookie*
 Title    Structural Phase Transitions in BaTi0 3 Studied via Perturbed Angular Correlations  
 Abstract    Phase transitions in the ferroelectric perovskite BaTi0 3 were studied for 111 In-implanted poly-crystalline samples by measuring the electric field gradients by means of Perturbed Angular Correla-tion spectroscopy. The phase transitions between the orthorhombic rhombohedral tetragonal cubic lattices were investigated in 2 -10 K steps, for increasing and decreasing temperatures, in order to determine their hysteresis. The transition parameters are compared with results from measurements of the spontaneous polarization, electric susceptibility and neutron scattering. 
  Reference    Z. Naturforsch. 55a, 242—246 (2000); received August 24 1999 
  Published    2000 
  Keywords    Perturbed Angular Correlations, BaTi0 3, Phase Transitions, Hysteresis, 1 " In 
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 TEI-XML for    default:Reihe_A/55/ZNA-2000-55a-0242.pdf 
 Identifier    ZNA-2000-55a-0242 
 Volume    55 
64Author    Ichi Suzuki, Shin'. Ichi, Ishimaru, Ryuichi IkedaRequires cookie*
 Title    Koh  
 Abstract    133 Cs NMR spin-lattice relaxation times(Ti) in crystalline Cs 2 CdI 4 were measured at 225 -373 K. The critical exponent (of T\ observed near the normal-incommensurate transition in the normal phase was determined to be 0.62 ± 0.03, in good agreement with the predicted value for three-dimensional XK-model. The frequency dependent T\ in the incommensurate phase could be explained by the fluctuation of amplitudon and small gap phason. 
  Reference    Z. Naturforsch. 55a, 339—342 (2000); received August 27 1999 
  Published    2000 
  Keywords    l33 Cs NMR, T\ \ Incommensurate, Phase Transition, Critical Exponent 
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 TEI-XML for    default:Reihe_A/55/ZNA-2000-55a-0339.pdf 
 Identifier    ZNA-2000-55a-0339 
 Volume    55 
65Author    E. Mikuli, A. Migdał-Mikuli, I. Natkaniec, J. MayerRequires cookie*
 Title    Phase Transitions and Water Dynamics of [Mn(H 2 0) 6 ](C10 4 ) 2 Studied by Differential Scanning Calorimetry and Neutron Scattering Methods  
 Abstract    DSC measurements performed at 95 -290 K have shown that [Mn(H 2 0) 6 ](C10 4) 2 possesses, besides a high-temperature phase, existing above 323 K, four low-temperature solid phases. The inelastic incoherent neutron scattering (IINS) spectra and neutron powder diffraction (NPD) pat-terns registered at 20 -290 K have supported the DSC results and provided evidence that the investigated substance possesses even more than five solid phases. The IINS spectra have shown that in the room-temperature phase, water molecules perform fast stochastic reorientation at the picosecond scale. The orientational disorder characteristic for the room-temperature phase can be easily overcooled and frozen. Even by relatively slow cooling at ca. 40 K/hour a metastable, orientational (protonic) glass phase is formed below ca. 160 K. Below ca. 100 K, a structural phase transition was observed by the NPD, however the IINS spectra indicate existence of the pure ordered low-temperature phase only after annealing the sample for a few hours at 100 K. On heating, a structural phase transition takes place at ca. 120 K, and at ca. 225 K water molecules begin fast reorientation. 
  Reference    Z. Naturforsch. 55a, 759—764 (2000); received July 7 2000 
  Published    2000 
  Keywords    Hexaaquamanganese(II) chlorate(VII), Phase Transitions, DSC, Neutron Scattering 
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 TEI-XML for    default:Reihe_A/55/ZNA-2000-55a-0759.pdf 
 Identifier    ZNA-2000-55a-0759 
 Volume    55 
66Author    Masahiko Suhara, Koichi ManoRequires cookie*
 Title    NQR and Phase Transitions in Hexachlorocyclopropane Crystal  
 Abstract    35 C1 NQR and DSC studies on phase transitions in hexachlorocyclopropane (HCCP), C 3 C1 6 , are reported. It is found that HCCP has three solid phases: A high temperature disordered phase (Phase I) above 301 K (no NQR spectrum was observed); a metastable phase (Phase II), which exhibited 6 NQR lines from 77 to 270 K; a low temperature phase (Phase III) in which a 24-multiplet of 35 C1 NQR lines at 77 K, the most complex multiplet spectrum ever reported was observed. DSC measurement shows a A-type transition at 301 K and a broad transition of very slow rate at 285 K. The structure and mechanism of phase transitions in HCCP crystal are discussed. 
  Reference    Z. Naturforsch. 45a, 339—342 (1990); received August 23 1989 
  Published    1990 
  Keywords    Nuclear quadrupole resonance, Phase transition, Crystal structure, Differential scan-ning calonmetry, Order-disorder transition 
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 TEI-XML for    default:Reihe_A/45/ZNA-1990-45a-0339.pdf 
 Identifier    ZNA-1990-45a-0339 
 Volume    45 
67Author    Stefan Jurga, Kazimierz Jurga, EduardC. Reynhardt, Piotr KatowskiRequires cookie*
 Title    A Proton NMR Study of n-Decylammonium Chain Dynamics in the Perovskite-type Layered Compound (C 10 H 21 NH3) 2 CdCl4  
 Abstract    A detailed proton second moment and spin-lattice relaxation time investigation of the bilayered compound (C 10 H 21 NH 3) 2 CdCl 4 is reported. In the low temperature phase the methyl group exe-cutes a classical threefold reorientation, while the NH 3 group is involved in a similar reorientation in an asymmetric potential well. Evidence for defect chain motions in this phase has been found, and infomation regarding the potential wells associated with these motions has been extracted from the data. In the high temperature phase, slow chain defect motions and fast fourfold reorientations of chains about their long axes, parallel to the normal to the bilayer, have been observed. 
  Reference    Z. Naturforsch. 48a, 563—569 (1993); received October 9 1992 
  Published    1993 
  Keywords    Bilayered compounds, Phase transition, Spin-lattice relaxation, Molecular motions, Defect motions 
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 TEI-XML for    default:Reihe_A/48/ZNA-1993-48a-0563.pdf 
 Identifier    ZNA-1993-48a-0563 
 Volume    48 
68Author    Motoko Kenmotsu, Hisashi Honda, Hiroshi Ohki, Ryuichi Ikeda, Tomoki Erata, Akira Tasaki, Yoshihiro FurukawaRequires cookie*
 Title    Ionic Dynamics in Plastic Crystal KNOz Studied by 39K and I5NNMR  
 Abstract    The spin-lattice relaxation time of 39K N M R observed in the low-temperature phase (T <264.1 K) of K N 0 2 is explained by the quadrupole mechanism contributed from a newly found N O J m otion. The in-plane C 3 reorientation and the overvall N 0 2 rotation as well as the self-diffusion were shown in the intermediate phase (T < 314.7 K) and the high-temperature plastic phase (T < melting point: 710 K), respectively, by observing 39K and 15N N M R relaxation times and 1SN lineshapes. 
  Reference    Z. Naturforsch. 49a, 247 (1994); received July 23 1993 
  Published    1994 
  Keywords    K e y words: Solid NM R, Q uadrupole relaxation, Plastic crystal, Phase transition, Chemical shift anisotropy 
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 TEI-XML for    default:Reihe_A/49/ZNA-1994-49a-0247.pdf 
 Identifier    ZNA-1994-49a-0247 
 Volume    49 
69Author    Tetsuo Asaji, Hideshi Tomizawa, Ryuichi IkedaRequires cookie*
 Title    Structural Phase Transition of N,N-Dimethylnitramine as Studied by 14N Nuclear Quadrupole Resonance  
 Abstract    The 14N nuclear quadrupole relaxation time and resonance frequencies v+, v_, and vd of N,N-dimethylnitramine were measured between 14 and 313 K. The frequency increase of v+ and v_ observed below Tc (108 K) is explained by the increase o f prc electrons in the am ino nitrogen caused by the deformation of the m olecular skelton, which is planar above Tc. The sharp Tip minima for v+ and v_ observed at Tc are attributed to the softening o f vibration modes on both sides of Tc. The fluctuation o f the nitrogen-hydrogen m agnetic dipolar interaction due to C H 3 reorientation was detected as a broad T'lQ minimum observed around 84 K. A logarithmic divergence of Tu31 observed on the high-temperature side o f Tc suggests the presence o f a diffusive or overdamped-type soft mode. 
  Reference    Z. Naturforsch. 49a, 253 (1994); received August 10 1993 
  Published    1994 
  Keywords    M olecular crystal, Phase transition, Soft mode, NQ R, Spin-lattice relaxation 
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 TEI-XML for    default:Reihe_A/49/ZNA-1994-49a-0253.pdf 
 Identifier    ZNA-1994-49a-0253 
 Volume    49 
70Author    K. Yamada, K. Isobe, T. Okuda, Y. FurukawaRequires cookie*
 Title    Successive Phase Transitions and High Ionic Conductivity of Trichlorogermanate (II) Salts as Studied by 35C1 NQR and Powder X-Ray Diffraction  
 Abstract    A series o f trichlorogermanate(II) salts (AG eCl3, A = Rb, Cs, C H 3N H 3, and (C H 3)4N) have been synthesized and characterized by 35C1 N Q R , 35C1 N M R , AC conductivity, DTA, and X-ray diffrac­ tion techniques. In the temperature range studied two, two, five, and four phases were confirmed for the Rb, Cs, C H 3N H 3, and (C H 3)4N salts, respectively. From the 35C1 N Q R and structural data, isolated pyramidal G eC l3 anions were recognized in the low temperature phases. With increasing temperature the relaxation times of the 35C1 N Q R decreased exponentially and the signals disap­ peared far below the melting point. This suggests that the reorientation of the anion about the pseudo three-fold axis is excited. With further increase in temperature, the ionic conductivity of C H 3N H 3G eC l3 and (C H 3)4N G eC l3 increased drastically at the phase transitions to their cubic perovskite phases (C H 3N H 3G eC l3: a = 10-1 S m -1 at 400 K, (C H 3)4N G eC l3: a = 5 x 10-2 S m _1 at 420 K). The mobile ion was confirmed to be the chloride ion by means of 35C1 N M R and X-ray diffraction. 
  Reference    Z. Naturforsch. 49a, 258 (1994); received July 23 1993 
  Published    1994 
  Keywords    35C1 N Q R, 35C1 N M R, Ionic conductivity, Rietveld analysis, Phase transition 
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 TEI-XML for    default:Reihe_A/49/ZNA-1994-49a-0258.pdf 
 Identifier    ZNA-1994-49a-0258 
 Volume    49 
71Author    Hirokazu Nakayama, Taro Eguchi, Nobuo NakamuraRequires cookie*
 Title    Phase Transitions in 4,4'-Dichlorobenzophenone as Studied by 3SC1FT-NQR  
 Abstract    The temperature dependence of 35C1 N Q R frequencies in 4,4'-dichlorobenzophenone was m ea­ sured between 9.3 and 372 K by the pulse Fourier-transform method. Successive phase transitions were observed at 189 and 194 K. Concerning these phase transitions, the curious thermal hysteresis phenom enon found in a previous N Q R experiment was not reproduced in the present study. It also follow s that N Q R indicates another phase transition around 220 K, although no thermal anom aly was detected there by DTA. Tentative explanations for these three phase transitions are presented in relation to the incommensurability between 189 and 220 K. In addition, a novel phase transition was found to occur at 331 K according to both DTA and 35C1 N Q R. A single N Q R line observed at room temperature splits into two com ponents above 331 K, suggesting that the symmetry above 331 K is lower than that at room temperature. This is the behavior o f re-entrant phase transition, and it reveals the quasi-continuous nature. 
  Reference    Z. Naturforsch. 49a, 267 (1994); received August 21 1993 
  Published    1994 
  Keywords    35C1 N Q R, 4, 4'-dichlorobenzophenone, Phase transition, Incomm ensurate phase 
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 TEI-XML for    default:Reihe_A/49/ZNA-1994-49a-0267.pdf 
 Identifier    ZNA-1994-49a-0267 
 Volume    49 
72Author    Hisashi Honda, Shin'. Ichi Ishimaru, Noriko Onoda-Yamamuro, Ryuichi IkedaRequires cookie*
 Title     
 Abstract    y n a m ic s o f N i t r i te I o n s in th e I o n ic P la s tic C r y s ta l T IN O 2 s tu d ie d b y 15N a n d 205T1 N The temperature dependences of the NMR spin-lattice and spin-spin relaxation times and the NMR spectra of 15N in T115N02 were observed in the plastic phase (282.4 K < T < 459 K) and the low-temperature phase. From the analysis of 15N NMR data, we attributed the motion reported in dielectric and TI NMR studies in the low-temperature phase to the 180°-flip of NO^~ ions which takes place with an activation energy of 14 kJ mol-1. In the plastic phase, we detected isotropic NOJ reorientation with an activation energy of 13.5 kJ mol-1 and a new anionic motion with 10 kJ mol-1. 
  Reference    Z. Naturforsch. 50a, 871—875 (1995); received June 16 1995 
  Published    1995 
  Keywords    Solid NMR, Spin-lattice relaxation, Plastic crystal, Phase transition, Chemical shift anisotropy 
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 TEI-XML for    default:Reihe_A/50/ZNA-1995-50a-0871.pdf 
 Identifier    ZNA-1995-50a-0871 
 Volume    50 
73Author    Tsutomu Okuda, Shusaku Gotou, Toshirou Takahashi, Hiromitsu Terao, Koji YamadaRequires cookie*
 Title    Structure and Successive Phase Transitions of RGeBr 3 (R = Alkylammonium) Studied by Means of NQR  
 Abstract    A series of tribromogermanate(II) complexes RGeBr 3 (R = CH 3 NH 3 , (CH 3) 2 NH 2 , (CH 3) 4 N, C 2 H 5 NH 3 , (C 2 H 5) 4 N) have been synthesized and characterized by 81 Br NQR, AC conductivity, DTA, and X-rax diffraction. These measurements revealed the presence of successive phase transi-tions in these complexes. The crystal structures of Phases I and II in (NH 3) 4 NGeBr 3 were derived from the Rietveld analysis of powder X-ray diffraction. The electric conductivity was considerably high in CH 3 NH 3 GeBr 3 and (NH 3) 4 NGeBr 3 . The conduction mechanism is discussed on the basis of 81 Br NQR spin-lattice relaxation times and crystal structures. 
  Reference    Z. Naturforsch. 51a, 686—692 (1996); received October 10 1995 
  Published    1996 
  Keywords    81 Br NQR, T x, Phase Transition, Ionic Motion, Ionic Conductivity 
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 TEI-XML for    default:Reihe_A/51/ZNA-1996-51a-0686.pdf 
 Identifier    ZNA-1996-51a-0686 
 Volume    51 
74Author    K. Yamada, T. Ohtani, S. Shirakawa, H. Ohki, T. Okuda, T. Kamiyama, K. OikawaRequires cookie*
 Title    Phase Transition of C 5 H 5 NHSbBr 4 Having a Hypervalent Bond: A 2 H NMR and X-Ray Diffraction Study* [Phase Transition of C 5 H 5 NHSbBr 4 l  
 Abstract    The second order phase transition at 253 K of pyridinium tetrabromoantimonate(III), C 5 H 5 NHSbBr 4 , has been characterized by means of X-ray diffraction and 2 H NMR. As was suggested from the 81 Br NQR spectra, the Rietveld refinements of the X-ray diffraction patterns at 297 K and 116 K confirm the structural change of the anion from SbBr 4 to SbBr 3 • Br -. The line shape analysis of the 2 H NMR using the deuterated analog revealed that the librational amplitude of the pyridinium ring about the axis normal to the plane increased with temperature and its rms amplitude reaching ca. 25° at T c . The librational motion may induce the phase transition breaking the hydrogen bonds of the type N-H -Br. However, nearest-neighbor 2n/6 jump or reorientation such as seen in benzene were not observed even at 350 K. 
  Reference    Z. Naturforsch. 51a, 739—744 (1996); received October 11 1995 
  Published    1996 
  Keywords    2 H NMR, 81 Br NQR, Rietveld analysis, Phase transition, Hypervalent bond 
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 TEI-XML for    default:Reihe_A/51/ZNA-1996-51a-0739.pdf 
 Identifier    ZNA-1996-51a-0739 
 Volume    51 
75Author    Yoshio Kume, Tetsuo AsajiRequires cookie*
 Title    Chlorine-35 NQR Study of a Structural Phase Transition in (ND 4 ) 2 PdCV  
 Abstract    Temperature dependences of 35 C1 NQR frequencies and spin-lattice relaxation times were measured at 4.2 to 400 K for natural and deuterated ammonium hexachloropalladate. It was confirmed that only the deuterated salt undergoes a first order phase transition at 30 K. The crystal structure of the low-tem-perature phase is predicted to be the same as that of the deuterated ammonium hexachloroplatinate and hexachloroplumbate. The mechanism of the deuteration-induced phase transition is discussed. 
  Reference    Z. Naturforsch. 53a, 514—517 (1998); received March 24 1998 
  Published    1998 
  Keywords    Isotope Effect, Phase Transition, Chlorine NQR, Spin-lattice Relaxation, Deuterated Ammonium Hexachloropalladate 
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 TEI-XML for    default:Reihe_A/53/ZNA-1998-53a-0514.pdf 
 Identifier    ZNA-1998-53a-0514 
 Volume    53 
76Author    Hiromitsu Terao, Masao Hashimoto\, Tsutomu Okuda, Alarich WeissRequires cookie*
 Title    Phase Transitions and Crystal Structure of Dimethylammonium Tribromomercurate(II), (CH 3 ) 2 NH 2 HgBr 3 , as Studied by 81 Br NQR and Single Crystal X-ray Diffraction  
 Abstract    The temperature dependence of the 81 Br NQR frequencies of the title compound has revealed the presence of three phases (I, II and III, in the order of decreasing temperature): T cl (II -1) = (318 ± 10) K and T c2 (III -II) = (202 ± 1) K. The transitions were confirmed by thermal analysis (DTA). Both of the II-I and I-II transitions exhibited strong hysteresis (/. e., superheating and supercooling, respectively). The crystal data, determined by single crystal X-ray diffraction, are: monoclinic, space group P2/a, a = 1384.8(3), b = 934.7(4), c = 1452.0(2) pm, ß = 104.10(1)°, Z= 8, R = 0.076. The crystal has two crystallographically independent cations (CH 3) 2 NH 2 + and an infinite chain of anions almost in the c-direction. The anion chain is considered to consist of a HgBr 2 molecule and two different HgBr 4 2 ~ anions which are interconnected via weak intermolecular Hg-Br bonds. The splitting patterns of the 8 'Br NQR spectra indicate that rearrangements of the Hg-Br bonds are slight at the III-II transition but serious at the II-I transition. Some of the 81 Br NQR lines show anomalous temperature coefficients, attributable probably to thermal motions of cations. 
  Reference    Z. Naturforsch. 53a, 559—567 (1998); received January 26 1998 
  Published    1998 
  Keywords    (CH 3 ) 2 NH 2 HgBr 3, X-Ray Analysis, NQR, Phase Transition, Crystal Structure 
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 TEI-XML for    default:Reihe_A/53/ZNA-1998-53a-0559.pdf 
 Identifier    ZNA-1998-53a-0559 
 Volume    53 
77Author    Takahiro Iijima, Motohiro Mizuno, Masahiko SuharaRequires cookie*
 Title    H NMR Study of Molecular and Electron Spin Dynamics in Paramagnetic [Co(H 2 0) 6 ][SiF 6 ]  
 Abstract    The temperature dependences of 2 H NMR spectra and the spin-lattice relaxation time T\ were measured for [Co(H20)f,][SiF6]. The variation of the spectrum above room temperature can be explained by the reorientation of [Co(H20)fi] 2+ about the C3 axis. The activation energy E a and the jumping rate at infinite temperature fco for the three site jump of [Co(H20)6] 2+ were obtained as 82 kJmol -1 and 2x 10 17 s~ 1 from the spectral simulation. Below room temperature, the spectral line shape was dominated by the 180° flip of the water molecule. The minimum of T\ caused by the 180° flip of the water molecule was observed at ca. 260 K. The jumping rate of the 180° flip of the water molecule was estimated from the 2 H NMR T\ and the spectral simulation. E* = 38 kJmol -1 and fco = 6x 10 l5 s -1 for the 180° flip of the water molecule were obtained from T\. 
  Reference    Z. Naturforsch. 55a, 173—177 (2000); received August 23 1999 
  Published    2000 
  Keywords    Phase Transition, 2 H NMR, Nuclear Quadrupole Interaction, Paramagnetic Shift, Molecular Dynamics 
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 Identifier    ZNA-2000-55a-0173 
 Volume    55 
78Author    Motohiro Mizuno, Takahiro Iijima, Kengo Orii, Masahiko SuharaRequires cookie*
 Title    Water Molecular Motion and Hydrogen Bond in Paramagnetic [Cu(H 2 0) 6 ][PtCl 6 ] as Studied by Single Crystal 2 H NMR  
 Abstract    The temperature and angular dependences of the 2 H NMR spectrum were measured for single crystal [Cu(H 2 0) 6 ] [PtCl 6 ]. (e 2 Qq/h, r?) = (132 kHz, 0.72) were obtained for the D nucleus averaged by the fast 180° flip of the water molecule at 297 K. D,(236 kHz, 0.10) and D 2 (246 kHz, 0.09) were obtained for two unequal D nuclei of the water molecule at 133 K. Below T c , at least three nonequivalent waters were found to exist. The jumping rate for the 180° flip of the water molecule (k) was obtained from the simulation of 2 H NMR spectra at //o||[l 11] direction. The activation energy E d and the jumping rate at infinite temperature were estimated from the temperature dependence of k to be 24kJmol _1 and 1 x 10 13 s -1 . 
  Reference    Z. Naturforsch. 55a, 178—182 (2000); received August 23 1999 
  Published    2000 
  Keywords    Phase Transition, 2 H NMR, Nuclear Quadrupole Interaction, Paramagnetic Shift, Molecular Dynamics 
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 Identifier    ZNA-2000-55a-0178 
 Volume    55 
79Author    Hiromitsu Terao, Masao Hashimoto, Shinichi Hashimoto, Yoshihiro FurukawaRequires cookie*
 Title    Studies of Structure and Phase Transition in [C(NH 2 ) 3 ]HgBr 3 and [C(NH 2 ) 3 ]HgI 3 by Means of Halogen NQR, NMR, and Single Crystal X-Ray Diffraction  
 Abstract    The crystal structure of [C(NH 2) 3 ]HgBr 3 was determined at room temperature: monoclinic, space group C2/c, Z = 4, a = 775.0(2), b = 1564.6(2), c = 772.7(2) pm, ß = 109.12(2)°. In the crystal, almost planar HgBr 3 ~ ions are connected via Hg -Br bonds, resulting in single chains of trigonal bipyramidal HgBr 5 units which run along the c direction. [C(NH 2) 3 ]HgI 3 was found to be isomorphous with the bromide at room temperature. The temperature dependence of the halogen NQR frequencies (77 < 77K < ca. 380) and the DTA measurements evidenced no phase transition for the bromide, but a second-order phase transition at (251 ± 1) K (7 tl) and a first-order one at (210 ± 1) K (T C2) for the iodide. The transitions at T C2 are accompanied with strong supercooling and significant superheating. The room temperature phase (RTP) and the intermediate temperature phase (ITP) of the iodide are characterized by two I(m =i/2~3/2) NQR lines which are assigned to the terminal and the bridging I atoms, respectively. There exist three lines in the lowest temperature phase (LTP), indicating that the resonance line of the bridging atom splits into two. The signal intensities of the 127 I (m =i/2—3/2) NQR lines in the LTP decrease with decreasing temperature resulting in no detection below ca. 100 K. The 127 I(m =i/ 2 ~3/2) NQR frequency vs. temperature curves are continuous at T CL , but they are unusual in the LTP. The T X vs. Tcurves of 'H NMR for the bromide and iodide are explainable by the reorientational motions of the cations about their pseudo three-fold axes. The estimated activation energies of the motions are 35.0 kJ/mol for the bromide, and 24.1, 30.1, and 23.0 kJ/mol for the RTP, FTP, and LTP of the iodide, respectively. 
  Reference    Z. Naturforsch. 55a, 230—236 (2000); received August 23 1999 
  Published    2000 
  Keywords    [C(NH 2 ) 3 ]HgX 3, Crystal Structure, Phase Transition, NQR, 'H NMR 
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 TEI-XML for    default:Reihe_A/55/ZNA-2000-55a-0230.pdf 
 Identifier    ZNA-2000-55a-0230 
 Volume    55 
80Author    N. Ulbrich, W. Tröger, T. Butz, P. Blaha, Nukleare FestkörperphysikRequires cookie*
 Title    Investigation of the Negative Thermal Expansion of ZrW 2 O g  
 Abstract    The negative thermal expansion in ZrW 2 0 8 was investigated on a microscopic scale by temperature dependent measurements of the electric field gradients at the nuclear probe 187 W (ß~) 187 Re using time differential perturbed angular correlation spectroscopy. Two distinct nuclear quadrupole interactions I VJ? cl l= 18.92(4) • 10 21 V/m 2 , q Rcl = 0.0 and I V5 e2 l = 4.55(2) • 10 21 V/m 2 , r? Re2 = 0.053(3) were observed at 295 K, which are assigned to the two crystallographically distinct W0 4 tetrahedra of the room temperature structure. Ab initio calculations of electron densities and electric field gradients with 1:7 Re-impurities using the full potential linearized augmented plane wave package WIEN97 yield the electric field gradients VJ? C| = 12.63 • 10 21 V/m 2 ,7y Rcl = 0.0 and vJ? e2 =4.90 • 10 21 V/m 2 , rj Re2 =0.0. The observed temperature dependence of the nuclear quadrupole interactions agrees well with the structu-ral phase transition at 428 K observed by neutron and x-ray diffraction. Our experiments corroborate the suggested mechanism of coupled librations of rigid Zr0 6 octahedra and W0 4 tetrahedra, which is an alternative description of transverse vibrations of oxygen atoms in Zr-O-W bonds, for the negative thermal expansion in ZrW 2 0 8 . 
  Reference    Z. Naturforsch. 55a, 301—310 (2000); received October 28 1999 
  Published    2000 
  Keywords    ZrW 2 0 8, Negative Thermal Expansion, Phase Transition, Time Differential Perturbed Angular Correlation (TDPAC), Hyperfine Spectroscopy 
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 TEI-XML for    default:Reihe_A/55/ZNA-2000-55a-0301.pdf 
 Identifier    ZNA-2000-55a-0301 
 Volume    55 
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