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'Phase Transitions' in keywords Facet   Publication Year 1995  [X]
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Publication Year
1995[X]
1Author    Barbara Szafrańska, Zdzisław PająkRequires cookie*
 Title     
 Abstract    o le c u la r M o tio n in S o lid T e tr a e th y l-a n d T e tra p ro p y la m m o n iu m T e tr a f lu o r o b o r a te s Proton and fluorine NMR second moments and spin-lattice relaxation times for polycrystalline tetraethyl-and tetrapropylammonium tetrafluoroborates have been measured over a wide range of temperatures. Solid-solid phase transitions were found for both compounds and confirmed by DSC. Methyl group C3 reorientation followed by more complex cation motions was evidenced in the low temperature phases. Overall cation reorientation characterises the high temperature phases of both compounds. Isotropic anion reorientation was found in both salts in both phases. 
  Reference    Z. Naturforsch. 50a, 584—588 (1995); received August 15 1994 
  Published    1995 
  Keywords    NMR, Molecular motions, Phase transitions 
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 TEI-XML for    default:Reihe_A/50/ZNA-1995-50a-0584.pdf 
 Identifier    ZNA-1995-50a-0584 
 Volume    50 
2Author    M. Grottel3, A. Kozakb, Z. PająkRequires cookie*
 Title    l H a n  
 Abstract    d 19F N M R S tu d y o f C a tio n a n d A n io n M o tio n s in G u a n id in iu m F lu o r o a n tim o n a te s Proton and fluorine NMR linewidths, second moments, and spin-lattice relaxation times of polycrystalline [C(NH2)3]2SbF5 and C(NH2)3SbF6 were studied in a wide temperature range. For the pentafluoroantimonate, C3-reorientation of the guanidinium cation and C4-reorientation of the SbF5 anion were revealed and their activation parameters determined. The dynamical inequivalence of the two guanidinium cations was evidenced. For the hexafluoroantimonate, two solid-solid phase transitions were found. In the low temperature phase the guanidinium cation undergoes C3 reorien­ tation while the SbF6 anion reorients isotropically. The respective activation parameters were derived. At high temperatures new ionic plastic phases were evidenced. 
  Reference    Z. Naturforsch. 50a, 742—748 (1995); received March 2 1995 
  Published    1995 
  Keywords    NMR, Molecular Motions, Phase transitions 
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 TEI-XML for    default:Reihe_A/50/ZNA-1995-50a-0742.pdf 
 Identifier    ZNA-1995-50a-0742 
 Volume    50 
3Author    Hiroyuki Ishida, Hironobu Maeda, Akiko Hirano, Tamotsu Fujimoto, Yoshihiro Kubozono, Setsuo Kashino, Shuichi EmuraRequires cookie*
 Title    E X A F S S tu d y o n th e P h a s e T r a n s itio n ( P h a s e a ' -5) in C H 3 N H 3 I  
 Abstract    The local structure of CH3NH3I around the I" ion in Phase a 'and 8 was studied by iodine K-edge EXAFS. The crystal structure in Phase a ' was redetermined by single crystal X-ray diffraction. The Debye-Waller factor <r(2) derived from EXAFS spectra shows an anomalous behavior around the order-disorder transition temperature from Phase 8 to a '. The phase transition has been interpreted as the disordering process which involves not only the H atoms but also the C atoms in the cation. 
  Reference    Z. Naturforsch. 50a, 876—880 (1995); received June 16 1995 
  Published    1995 
  Keywords    Crystal structure, EXAFS, Phase transition, X-ray diffraction 
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 TEI-XML for    default:Reihe_A/50/ZNA-1995-50a-0876.pdf 
 Identifier    ZNA-1995-50a-0876 
 Volume    50 
4Author    M. Arietta, S. Schriewer-Pöttgen, Wolfgang JeitschkoRequires cookie*
 Title    Two Modifications of Hg5Re2O 10  
 Abstract    The previously reported mercury perrhenate Hg5 Re2O 10, prepared hydrothermally, has now been obtained by reaction of HgO with the mercury(II) metaperrhenate H g (R e 0 4)2 in sealed silica tubes. A second modification o f this compound can be obtained by reaction of elem ental mercury with H g (R e 0 4)2 also in sealed silica tubes. Its crystal structure has been determined from single-crystal X-ray data: P 2 x/c, a -861.5(1), b = 1200.9(2), c = 1203.9(2) pm, ß = 97.15(1)°, Z = 4, R = 0.024 for 1733 structure factors and 105 variables. Both modifi­ cations may be represented by the formula H g2+-2H g20 -2 R e 0 4_, indicating that mercury occurs in oxidation states I and II. In both modifications the mercury and some oxygen atoms form two-dimensionally infinte, puckered, cationic nets of the composition (H g2+-2H g20)" , which are separated by the R e 0 4~ tetrahedra. In the modification reported earlier the mer­ cury oxygen nets consist of condensed 16-membered rings, while the nets of the present modification contain 10-and 22-membered rings. 
  Reference    Z. Naturforsch. 50b, 1335—1339 (1995); received February 27 1995 
  Published    1995 
  Keywords    Crystal Structure, Mercury Perrhenates, Phase Transitions 
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 TEI-XML for    default:Reihe_B/50/ZNB-1995-50b-1335.pdf 
 Identifier    ZNB-1995-50b-1335 
 Volume    50 
5Author    G. H., C. A., J. Zaleskia, G. Batorb, R. JakubasbRequires cookie*
 Title     
 Abstract    ie le c tr ic P r o p e r tie s a n d C h a r a c te r is a tio n o f th e S u p e rio n ic P h a s e o f [ C (N H 2) 3]2S b C l 5* [ C (N H 2) 3]C l (GHCA undergoes four phase transitions at Tcl = 402 K, Tc2 = 373 K, Ta = 162 K, and TcA = 146 K. Below Tc3 it possesses pyroelectric properties with the spontaneous polarization vector (Ps) in the ac plane and the maximum along the c axis equal to 8 pC/m2. Dielectric dispersion studies of GHCA show that the main dielectric dispersion connected probably with collective motions of chlorine ions is above 1GHz. For the phase transition at Tc2 to a superionic phase the thermal dilatation and electric conductivity were measured. The anomalies of the electric conductivity at Tc2 and T x were observed with large values of <j(10"3 S/m) above Tcl. The guanidinium cations above Tc2, besides reorientational motions, undergo slow self diffusion. 
  Reference    Z. Naturforsch. 50a, 888—892 (1995); received February 20 1995 
  Published    1995 
  Keywords    Guanidinium, chloroantimonate, phase transition, DSC, dilatometric, pyroelectric, electric conductivity 
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 TEI-XML for    default:Reihe_A/50/ZNA-1995-50a-0888.pdf 
 Identifier    ZNA-1995-50a-0888 
 Volume    50 
6Author    T. Brückert, D. Büsing, A. Würflinger, S. UrbanRequires cookie*
 Title      
 Abstract    h e r m a l A n a ly s is (D T A) a n d D ie le c tr ic S tu d ie s o f 4 -(tra n s -4 -H e p ty l-C y c lo h e x y l) -b e n z o n itr ile (7 P C H) u n d e r H ig h P r e s s u r e With the aid of DTA the phase diagram of 4-(trans-4-heptyl-cyclohexyl)-benzonitrile, 7PCH, was redetermined. Dielectric studies on the static and complex permittivity have been performed on 7PCH in the pressure range 0.1 -220 MPa, the frequency range 1 kHz-13 MHz and the temperature range 290-380 K. For the slow relaxation process in the nematic phase, characterized by the relaxa­ tion time Tjj , we have calculated the activation volume, A* V u, of about 80 to 60 cm3/mol (decreasing with increasing temperature), and the activation enthalpy, A *Hn, of approximately 70 kJ/mol. The isochoric activation energy, A* Un, amounts to about 36 kJ/mol. The pressure dependence of A * Hu is less pronounced compared with previous findings for 5PCH and 7CB. Estimates of t 0 (extrapo­ lated from the relaxation time in the isotropic phase) allow the calculation of the retardation factor gu = Tn/t0 that is analysed in terms of theories of Martin-Meier-Saupe and Coffey in order to evalu­ ate the nematic potential q. Using data for the order parameter 5 from NMR studies it was possible to determine the strength of the interaction potential in the nematic phase and to check the relation q~S which is valid at p = const., but not at V= const. The results are compared with recent findings for other homologous series. 
  Reference    Z. Naturforsch. 50a, 977—983 (1995); received August 25 1995 
  Published    1995 
  Keywords    Dielectric Relaxation, High Pressure, Liquid Crystals, Activation Parameters, Phase Transitions 
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 TEI-XML for    default:Reihe_A/50/ZNA-1995-50a-0977.pdf 
 Identifier    ZNA-1995-50a-0977 
 Volume    50 
7Author    Marcos Luján, Frank Kubel, Hans SchmidRequires cookie*
 Title    Crystal Growth, Room Temperature Crystal Structure and Phase Transitions of K M nP04  
 Abstract    Single crystals of K M nP 04 grown in a KC1 flux show ferroelastic domains. The structure was determ ined on an optically controlled single domain crystal by X-ray diffraction methods. The cell is triclinic with dimensions a = 5.4813(5), b = 8.627(1), c = 8.887(1), in A, a = 87.73(1)°, ß = 89.10(1)°, y = 88.01(1)°, VM = 419.6(1) A 3 and Z = 4. The structure is closely related to the stuffed /3-tridymite type. DTA experiments between room tem perature and 1000 °C and polarized light microscopy observations showed four phase transitions: at 165, 330, 353 and 707 °C. 
  Reference    Z. Naturforsch. 50b, 1210—1214 (1995); received February 20 1995 
  Published    1995 
  Keywords    Manganese Potassium Orthophosphate, Crystal Structure, Crystal Growth, Phase Transitions 
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 TEI-XML for    default:Reihe_B/50/ZNB-1995-50b-1210.pdf 
 Identifier    ZNB-1995-50b-1210 
 Volume    50 
8Author    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