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2000 (1)
1999 (1)
1998 (1)
1Author    R. Tchukvinskyi, R. Cach, Z. CzaplaRequires cookie*
 Title    Dielectric Study of the Ferroelectric Phase Transition in DMAGaS Crystal  
 Abstract    Electric permittivity measurments as functions of temperature at constant dc electric field and as func-tions of the dc electric field at constant temperatures in the paraelectric phase have been performed for DMAGaS crystal. The changes of the permittivity maximum with the electric field intensity evidence the first-order character of the ferroelectric phase transition at T cX . The field dependence of the permit-tivity e(E) in the paraelectric phase is discussed, using the classical electric equation of state. A meth-od for the determination of the corresponding coefficients is proposed. The obtained B and C coeffi-cients, together with double hysteresis loop observed above T cl prove the first-order character of the ferroelectric phase transition in DMAGaS crystal. 
  Reference    Z. Naturforsch. 53a, 105—111 (1998); received October 15 1998 
  Published    1998 
  Keywords    Ferroelectricity, Phase Transition, Dielectric Properties 
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 TEI-XML for    default:Reihe_A/53/ZNA-1998-53a-0105.pdf 
 Identifier    ZNA-1998-53a-0105 
 Volume    53 
2Author    Z. Czapla, S. Dacko, B. KosturekRequires cookie*
 Title    Ferroelectricity and Phase Transitions in Pyridinium Periodate Single Crystal  
 Abstract    Single crystals of pyridinium periodate were grown, and their physical properties were studied. Anomalies of the electric permittivity and birefringence were observed at T CL = 321 K and T C2 = 211 K. These observations gave evidences for the existence of three phases denoted as I, II, and III. Hysteresis loops were observed both in phase II and III. Pyroelectric measurements showed two anomalies at T CL and T C2 . The anomaly at T CL is related to the transition between a para-and ferroelectric phase, and the anomaly at T cl to the transition between two ferroelectric phases. 
  Reference    Z. Naturforsch. 55a, 891—894 (2000); received August 8 2000 
  Published    2000 
  Keywords    Phase Transitions, Ferroelecticity, Dielectric Properties, Birefringence 
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 TEI-XML for    default:Reihe_A/55/ZNA-2000-55a-0891.pdf 
 Identifier    ZNA-2000-55a-0891 
 Volume    55 
3Author    Stanislaw Urban, Albert WürflingerRequires cookie*
 Title    High Pressure Dielectric Studies of a Substance with the Smectic A 1 Phase  
 Abstract    The results of dielectric studies of 5-n-hexyl-2-(4'-isothiocyanato)-l,3-dioxane (6DBT) in the smec-tic A, phase at pressures up to 150 MPa and temperatures up to 340 K are presented. The low frequen-cy relaxation time T\\ (/?, T) yields the activation volume A # V|| = RT(d ln Tjj/9/>) r and activation enthal-py A # //jj = R(d ln T||/37) p . The calculated values of these parameters are compared with those ob-tained recently for n-octyl-cyanobiphenyl (8CB) forming the smectic A d phase. In the case of 6DBT both these quantities are practically constant, whereas those for 8CB decrease, when going away from the phase transitions isotropic -smectic A] (6DBT) or nematic -smectic A d (8CB). These differences support our earlier conclusion that increase of pressure leads to a breaking of the antiparallel associa-tions of cyanobiphenyl molecules in the smectic as well as in the nematic phases. 
  Reference    Z. Naturforsch. 54a, 455—458 (1999); received July 12 1999 
  Published    1999 
  Keywords    Liquid Crystal; Smectic A, Dielectric Properties, High Pressure 
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 TEI-XML for    default:Reihe_A/54/ZNA-1999-54a-0455.pdf 
 Identifier    ZNA-1999-54a-0455 
 Volume    54