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1999 (2)
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1Author    R. Jakubas, G. Bator, M. Foulon, J. Lefebvre, J. MatuszewskiRequires cookie*
 Title    Structural Phase Transitions in (/i-C 3 H 7 NH3) 2 SbBr 5  
 Abstract    Dielectric, DSC, thermal expansion and preliminary X-ray diffraction studies on (/i-C 3 H 7 NH3) 2 SbBr 5 are reported. It was found that this crystal undergoes a complex sequence of phase transitions. On cooling: phase I phase II at 188.7 K (continuous), II -» • III at 165 K (1st order, z!S = 26.8 J/mol K), III IV at 137 K (1st order, 1.6 J/mol K). On heating: IV III at 154 K, III II' at 168 K, II' -> II at 177 K (1st order, 2.8 J/mol K), II I at 189 K. All 1st order phase transitions are likely due to the motion of the n-C 3 H 7 NH3 cations. The dielectric dispersion studies between 100 Hz-1 MHz within the phases I and II indicate a fast reorientational motion of dipoles with T < 10" 7 s. 
  Reference    Z. Naturforsch. 48a, 529—534 (1993); received October 7 1992 
  Published    1993 
  Keywords    Alkylammonium halogenoantimonates, Phase transition, Dielectric, DSC, Thermal expansion 
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 TEI-XML for    default:Reihe_A/48/ZNA-1993-48a-0529.pdf 
 Identifier    ZNA-1993-48a-0529 
 Volume    48 
2Author    J. Zaleski, R. JakubasRequires cookie*
 Title    The Dielectric and Dilatometric Single Crystal Studies of Phase Transitions in a New Member of Family of Halogenoantimonates(III) [C(NH2)3l2SbCl5* [C(NH2)3]C1  
 Abstract    The results of dielectric, dilatometric and DSC studies on a new member of the family of alkylammonium halogenoantimonates ([(C(NH2)3]2SbCl5 • [(C(NH2)3]C1) are presented. This com­ pound undergoes three phase transitions at 146 K, 162 K, and 366 K. The two low temperature transitions are suggested to be of the displacive type and the high temperature one of the order-dis-order type. The character of temperature changes of the electric permittivity at the lowest temper­ ature transition suggest a polar phase below the transition temperature. 
  Reference    Z. Naturforsch. 49a, 709—713 (1994); received March 23 1994 
  Published    1994 
  Keywords    Phase transitions, Dielectric, Dilatometric, Halogenoantimonate, Guanidinium 
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 TEI-XML for    default:Reihe_A/49/ZNA-1994-49a-0709.pdf 
 Identifier    ZNA-1994-49a-0709 
 Volume    49 
3Author    P. Kędziora, J. Jadżyn, L. HellemansRequires cookie*
 Title    Nonlinear Dielectric Relaxation in Solutions of 6CHBT in Nonpolar Medium  
 Abstract    The frequency dependence of the nonlinear dielectric increment was studied for benzene solutions of the nematogenic molecule 4-(rra«s-4'-«-hexylcyclohexyl)isothiocyanatobenzene (QH^CyHx-Ph-N = C = S, 6CHBT) at 25°C. The increment was induced by a quasi-static electric field of high strength (10 7 V/m), and its relaxation was detected by an alternating field of low strength (10 2 V/m) in the fre-quency range 1 MHz-3 GHz. The results are discussed in the framework of Coffey's theory. 
  Reference    Z. Naturforsch. 54a, 585—589 (1999); received September 3 1999 
  Published    1999 
  Keywords    Dielectrics, Nonlinear Dielectric Increment, Nonlinear Relaxation 
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 TEI-XML for    default:Reihe_A/54/ZNA-1999-54a-0585.pdf 
 Identifier    ZNA-1999-54a-0585 
 Volume    54 
4Author    F. SchullerRequires cookie*
 Title    Dispersion Potentials between Atoms and Dielectric Bodies  
 Abstract    We derive a formula for the van der Waals interaction between an atom and a dielectric surface for both ground and excited state potentials. We compare our result with previously derived expressions involving the dielectric constant at purely imaginary frequencies. We also study the relationship between atom-dielectric and ordinary atom-atom van der Waals interaction. 
  Reference    Z. Naturforsch. 49a, 885—889 (1994); received July 6 1994 
  Published    1994 
  Keywords    Van der Waals potentials, Atoms, Dielectrics, Surface physics, Atomic spectroscopy 
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 TEI-XML for    default:Reihe_A/49/ZNA-1994-49a-0885.pdf 
 Identifier    ZNA-1994-49a-0885 
 Volume    49 
5Author    Phineus Markwick, Stanislaw Urban, Albert WürflingerRequires cookie*
 Title    High Pressure Dielectric Studies of 8CB in the Isotropic, Nematic, and Smectic A Phases  
 Abstract    The static and complex permittivity of 4-n-octyl-4'-cyanobiphenyl (8CB) has been measured for the isotropic, nematic and smectic A phases as functions of temperature and pressure. The ranges of 297 -361 K, 0.1 -220 MPa, and 0.1 -13 MHz, were covered. Only the parallel component of the complex permittivity, £*(/) = e'(f) — ie"(f), was measured. The relaxation times T||(p, T) as well as ris(p, T) were analysed at constant temperature, pressure and volumes yielding the activation volume, A ¥ V(T), activation enthalpy A^H(p), and activation energy lyU(V), respectively. All activation parameters calculated for the smectic A phase of 8CB are smaller than those obtained for the nematic phase. The activation energy constitutes approximately half of the activation enthalpy value in all three phases studied. The pressure study allowed to calculate the pressure dependence of the retardation factor g\\(p, T), from which the nematic potential q(p,T) can be derived. Using the relationships between g\\ and q/RT proposed by Kalmykov and Coffey, the order parameter (Piip, T)) was calculated as a function of pressure. 
  Reference    Z. Naturforsch. 54a, 275—280 (1999); received March 13 1999 
  Published    1999 
  Keywords    Liquid Crystals, 8CB, High Pressure, Dielectric, Thermodynamics, Order Parameter 
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 TEI-XML for    default:Reihe_A/54/ZNA-1999-54a-0275.pdf 
 Identifier    ZNA-1999-54a-0275 
 Volume    54