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'Phase transitions' in keywords Facet   Publication Year 1990  [X]
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Publication Year
1990[X]
1Author    J. Wąsicki, Z. Pająk, A. KozakRequires cookie*
 Title    Cation and Anion Reorientation at Phase Transition in Pyridinium Tetrafluoroborate  
 Abstract    Temperature dependences of and 19 F second moment and spin-lattice relaxation times for polycrystalline pyridinium tetrafluoroborate were measured. A phase transition was discovered at 202 K. A model of cation reorientation between inequivalent (low-temperature phase) and equiva-lent (high-temperature phase) equilibrium positions is proposed. Whether the anion reorients isotropically or about a symmetry axis cannot be decided. An analysis of cross-relaxation effects yielded activation parameters for cation and anion reorientation. The rotational correlation times for both ions converge just at the phase transition reaching the value of 10~ 10 s. 
  Reference    Z. Naturforsch. 45a, 33—36 (1990); received August 5 1989 
  Published    1990 
  Keywords    NMR, cross-relaxation, molecular motions, phase transitions 
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 TEI-XML for    default:Reihe_A/45/ZNA-1990-45a-0033.pdf 
 Identifier    ZNA-1990-45a-0033 
 Volume    45 
2Author    Masao Hashimoto, Akiko Shono, Yoshiyuki Mido, Haruo Niki, Hiroshi Hentona, Koichi ManoRequires cookie*
 Title    Narrowing of the 3 5 CI NQR Lines of Trichloroacetamide Caused by Its Ferroelectric Phase Transition  
 Abstract    Dielectric measurements on single crystals and DSC of the title compound (monoclinic, space group P2 X) revealed a ferroelectric transition at ca. 355 K (AH xs 0.5 kJ mol"Powder x-ray diffraction indicated that the high temperature phase is also monoclinic and the change in volume at the transition is very small. A displacement of hydrogen atoms is considered as responsible for the appearance of ferroelectricity. The 35 C1 NQR signals at ca. 77 K were considerably broad, but a drastic narrowing took place after the compound had once experienced the phase transition. A tentative assignment of the NQR spectrum was made from a calculation of the NQR frequencies based on the CNDO/2 method. Another phase transition was evidenced by a small drift of the DSC curve and a slight anomaly of the dielectric behavior around 358 K. The present *H NMR experi-ments gave no indication of the onset of torsional motion of the NH 2 group reported to occur at ca. 210 K. 
  Reference    Z. Naturforsch. 45a, 327—333 (1990); received August 26 1989 in revised form November 1 1989 
  Published    1990 
  Keywords    NQR, Phase transition, Ferroelectricity, Hydrogen bond, Disordered structure 
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 TEI-XML for    default:Reihe_A/45/ZNA-1990-45a-0327.pdf 
 Identifier    ZNA-1990-45a-0327 
 Volume    45 
3Author    J. Pirnat, J. Lužnik, Z. Trontelj, P. K. KadabaRequires cookie*
 Title    Iodine NQR and Phase Transitions in [N(CH 3 ) 4 ] 2 ZnI 4 * a  
 Abstract    Using a superregenerative NQR spectrometer, the temperature dependence of 127 I NQR spectra in [N(CH 3) 4 ] 2 ZnI 4 was measured between 167 and 335 K. The measurements confirm two known structural phase transitions at 219 and 257.5 K. The correspondence between the distinct regions of iodine NQR spectra and the crystal structure is discussed. The relation of [N(CH 3) 4 ] 2 ZnI 4 to the incommensurate family with the general formula X 2 YZ 4 and the high temperature (paraphase) crystal space group D^ (Pmcn) is studied. 
  Reference    Z. Naturforsch. 45a, 349—352 (1990); received August 23 1989 in revised form 25 November 1989 
  Published    1990 
  Keywords    NQR, phase transitions, ferroelectric, crystal structure, displacement modulation 
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 TEI-XML for    default:Reihe_A/45/ZNA-1990-45a-0349.pdf 
 Identifier    ZNA-1990-45a-0349 
 Volume    45 
4Author    Juan Murgich, Ismardo Bonalde, JoseA. AbaneroRequires cookie*
 Title    N Nuclear Quadrupole Resonance Study of the Phase Transitions of Ba[Fe(CN) 5 N0] -3H 2 0  
 Abstract    The 14 N nuclear quadrupole resonance (NQR) of the cyanides in Ba[Fe(CN) s NO] • 3H 2 0 (BNP) was observed between 77 and 293 K. Phase transitions exist at 118,131 (both weakly first order) and 233 K (second order). Most of the cyanides were perturbed by the structural changes except for one of the trans cyanides that was only affected by the transition at 131 K. The mechanism of the phase transitions is interpreted in terms of soft modes resulting from the ion rearrangement produced by the slowing down of the water molecules upon cooling. A comparison of the NQR spectrum of BNP with that of Na ? [Fe(CN) 5 NO] • 3H 2 0 showed that the substitution of Na + by Ba 2 produced only minor changes in the charge distribution of the nitroprusside ion. 
  Reference    Z. Naturforsch. 45a, 353—356 (1990); received August 25 1989 
  Published    1990 
  Keywords    Magnetic Resonance (NQR), Nitroprussides, Phase Transitions 
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 TEI-XML for    default:Reihe_A/45/ZNA-1990-45a-0353.pdf 
 Identifier    ZNA-1990-45a-0353 
 Volume    45 
5Author    J. Von CieminskiRequires cookie*
 Title    Modeling of High-Signal Electrostriction. I  
 Abstract    A thermodynamical calculation of high-signal electrostriction, especially of ferroelectric materials, is proposed. It permits to model the high-signal electrostriction of the paraelectric and the funda-mental switching behaviour of the ferroelectric phase. Extraordinary high-signal deformation curves can be explained, the influence of the thermodynamical coefficients can be estimated and the order of phase transitions can be determined experimentally from the high-signal deformation curves. 
  Reference    Z. Naturforsch. 45a, 1090—1094 (1990); received May 8 1990 
  Published    1990 
  Keywords    Electromechanical properties, Electrostriction, Ferroelectrics, Thermodynamic, Phase transition 
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 TEI-XML for    default:Reihe_A/45/ZNA-1990-45a-1090.pdf 
 Identifier    ZNA-1990-45a-1090 
 Volume    45 
6Author    J. Von CieminskiRequires cookie*
 Title    Modeling of High-Signal Electrostriction. II  
 Abstract    The predictions obtained with a thermodynamical method are compared with experimental results. Several materials which pass a ferroelectric phase transition of first or second order are investigated. The predictions correspond well with the experimentaly determined qualitative and quantitative features as to the field and temperature dependence. Finally, extraordinary strain-field curves are predicted and proved. 
  Reference    Z. Naturforsch. 45a, 1095—1101 (1990); received May 8 1990 
  Published    1990 
  Keywords    Electromechanical properties, Electrostriction, Ferroelectrics, Thermodynamic, Phase transition 
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 TEI-XML for    default:Reihe_A/45/ZNA-1990-45a-1095.pdf 
 Identifier    ZNA-1990-45a-1095 
 Volume    45 
7Author    H. Einz, Jürgen Beister, K. Arl Syassen, Jürgen KleinRequires cookie*
 Title    Phase Transition of N a3As under Pressure  
 Abstract    We have investigated the high pressure behaviour of N a3As by powder X-ray diffraction. At 3.6 G Pa the material undergoes a reversible phase transition from the N a3As structure (P 6 3/ mmc, a = 487.4(8) pm, c = 851.5(20) pm, Z = 2, at 3.6 G Pa) to the Li3Bi structure type (Fm 3m , a = 683.5(15) pm, Z = 4, at 3.6 GaP). The equation of states is given for the pressure range up to 26 GPa. Results are discussed with respect to structural properties of related A3BV-compounds. 
  Reference    Z. Naturforsch. 45b, 1388—1392 (1990); received M arch 7 1990 
  Published    1990 
  Keywords    High Pressure, Crystal Structure, Phase Transition 
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 TEI-XML for    default:Reihe_B/45/ZNB-1990-45b-1388.pdf 
 Identifier    ZNB-1990-45b-1388 
 Volume    45 
8Author    S. Mazzuca, L. SportelliRequires cookie*
 Title    Thermal Behaviour of Lymphocyte Membrane: ESR Investigation  
 Abstract    The order parameter, S, of the plasma membrane of in toto human peripheral blood lym­ phocytes was obtained by electron spin resonance spectroscopy in the temperature range 25-41 C. This membrane is completely in the liquid crystalline state above 31 C. In presence of the antigen ETB from Staphylococcus aureus at the concentration of 4 (ig/3 * 107 cells an overall decrease of the order parameter for this membrane is observed. The decrease of 5 is followed by an upwards shift at about 35 C of the temperature of the liquid crystalline state. 
  Reference    Z. Naturforsch. 45c, 1060—1062 (1990); received April 6 1990 
  Published    1990 
  Keywords    Plasma Membrane, Lymphocyte, Phase Transition, Staphylococcal Enterotoxin B, Spin Labeling 
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 TEI-XML for    default:Reihe_C/45/ZNC-1990-45c-1060.pdf 
 Identifier    ZNC-1990-45c-1060 
 Volume    45 
9Author    Koji Yamada, Takashi Matsui, Tomoko Tsuritani, Tsutomu Okuda, Sumio IchibaRequires cookie*
 Title    I-NQR, 119 Sn Mössbauer Effect, and Electrical Conductivity of MSnI 3 (M = K, NH 4 , Rb, Cs, and CH 3 NH 3 )  
 Abstract    In a series of MSnI 3 compounds (M = K, NH 4 , Rb, Cs, CH 3 NH 3) two types of coordination around the central Sn(II) were found by 127 I-NQR and powder X-ray diffraction techniques. They are square pyramidal (for M = NH 4 , Rb) and octahedral (for M = CH 3 NH 3). CsSnI 3 , on the other hand, showed a drastic structural change of the anion at 425 K from a square pyramid to a regular octahedron. Associated with this phase transition, the electrical conductivity increased from 4xlO~ 3 Scm _1 to about 10 2 S cm" 1 . This metallic modification was characterized by 127 I-NQR and 119 Sn Mössbauer spectroscopy. 
  Reference    Z. Naturforsch. 45a, 307—312 (1990); received August 24 1989 in revised form October 28 1989 
  Published    1990 
  Keywords    NQR, Mössbauer effect, Perovskite compound, Phase transition, Electrical conductivity 
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 TEI-XML for    default:Reihe_A/45/ZNA-1990-45a-0307.pdf 
 Identifier    ZNA-1990-45a-0307 
 Volume    45 
10Author    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