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1998 (1)
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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    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. Furtak, Z. Czapla, A. V. KitykRequires cookie*
 Title    Ultrasonic Studies of Ferroelectric Phase Transition in Gly-H 3 P0 3 Crystals  
 Abstract    The temperature behaviour of the longitudinal and transverse ultrasound wave velocities and attenuation in the region of the ferroelectric phase transition (T c — 225 K.) of the glycine phosphite (Gly-H 3 P0 3) crystals is studied. The obtained results are considered within the framework of phenomenological theory. 
  Reference    Z. Naturforsch. 52a, 778—782 (1997); received October 4 1997 
  Published    1997 
  Keywords    Ferroelectricity, Phase Transition, Ultrasonic Velocity, Attenuation 
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 TEI-XML for    default:Reihe_A/52/ZNA-1997-52a-0778.pdf 
 Identifier    ZNA-1997-52a-0778 
 Volume    52 
4Author    A. Petcov, A. Kirfel, K. Fischer, Fr KristallographieRequires cookie*
 Abstract    e n s o ria l R e p r e s e n ta tio n o f / ' f o r N b in L ith iu m -n io b a te , L i N b 0 3 Using Synchrotron radiation, the dependence of resonant phenomena (absorption, fluorescence and Raman scattering) on the angle between the polarisation plane of the incident radiation and the polar c-axis in ferroelectric Lithium-niobate, LiNb03, was studied in the vicinity of the Nb K-absorption edge. Applying the "optical theorem", the observed dipolar anisotropics can be explained in terms of the projection of the dipole momentum operator on the polarisation vector of the X-ray photons. 
  Reference    Z. Naturforsch. 43a, 388—390 (1988); received January 22 1988 
  Published    1988 
  Keywords    Synchrotron radiation, X-ray absorption, Anomalous dispersion, Ferroelectricity, LiNb03 
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 TEI-XML for    default:Reihe_A/43/ZNA-1988-43a-0388.pdf 
 Identifier    ZNA-1988-43a-0388 
 Volume    43