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1Author    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 
2Author    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 
3Author    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 
4Author    W. OsakRequires cookie*
 Title    Charge Transport and Relaxation in Triglycine Sulphate (TGS)  
 Abstract    Charging currents, J-V characteristics and electron conductivity have been measured in triglycine sulphate along three crystallographic directions: a, b and c. The measurements have been taken in a wide temperature range between — 196°C and 80 °C. It is found that the charging currents have short relaxation times in the directions: a and c and a long relaxation time along the ferroelec-tric b axis. The J-V characteristics in the direction of the a and c axes have the shapes characteristic for linear dielectrics with space charge limited currents. The J-V characteristic for the b axis depends on the temperature: In the region of the phase transition the Fridkin-Kreher formula (J cc F 4/3) is satisfied; for low temperatures characteristic agrees with SCLC theory for linear dielectrics with Gaussian traps energy distribution. The d.c. conductivity along the c axis is much higher than along the a and b axes. In the investigated temperature range, the electrical conductivity has an activation character. For — 100°C < T < -193°C there is: <roc(l/T) exp(-E/kT). The activation energy depends both on the crystallographic direction and on the temperature-range. For low temperatures, T < — 100 °C, the activation energies are very small (of the order of a few hundreds eV). Subject classification: 72 (Electronic transport in condensed matter); 77 (Dielectrics, piezoelectrics and ferroelectrics and their properties). 
  Reference    Z. Naturforsch. 52a, 621—628 (1997); received February 17 1997 
  Published    1997 
  Keywords    Ferroelectrics, J-V characteristics, Electrical conductivity 
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 TEI-XML for    default:Reihe_A/52/ZNA-1997-52a-0621.pdf 
 Identifier    ZNA-1997-52a-0621 
 Volume    52 
5Author    Wolfgang Jeitschko, HorstA. Mons, Ute Ch, ManfredH. Rodewald, MöllerRequires cookie*
 Title    The Crystal Structure of the Potential Ferroelectric Calcium Rhenate(VI, VII) CanRe4 0 24 and its Relation to the Structure of S rn 0 s40 24  
 Abstract    The title compound was prepared in well-crystallized form by thermal decomposition of Ca5Re20i2. Its structure was determined from single-crystal X-ray diffractometer data: /4 j, a = 1107.0(1), c = 1609.3(1) pm, Z = 4, R -0.056 for 4565 structure factors and 119 variable parameters. The calcium atoms occupy seven different sites with 8, 9, or 10 oxygen neighbors. The two different rhenium atoms are octahedrally coordinated by oxygen atoms with average Re-O distances of 193.1 and 187.7 pm for the six-and seven-valent rhenium atoms, respectively. The compound shows Curie-Weiss behavior with a magnetic moment of n exp = 1.15(±0.10) Pb per Re(VI) atom. The structure is closely related to that of Srn0s4024 which, however, crystallizes in the space group I2la. The difference between the two structures arises through the higher coordination numbers of the strontium atoms. It is suggested that at high temperature both compounds crystallize in the common higher symmetry space group I4\/a. Since CanRe4024 crystallizes in the pyroelectric class 4 this compound is expected to be ferroelectric. 
  Reference    (Z. Naturforsch. 53b, 31—36 [1998]; received October 17 1997) 
  Published    1998 
  Keywords    Crystal Structure, Ferroelectrics, Mixed Valence, Rhenates, Perrhenates 
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 TEI-XML for    default:Reihe_B/53/ZNB-1998-53b-0031.pdf 
 Identifier    ZNB-1998-53b-0031 
 Volume    53 
6Author    GaryL. Catchen, EdwardF. Hollinger, ToddM. RearickRequires cookie*
 Title    Characterizing Phase Transitions in the Perovskites PbTi0 3 and BaTi0 3 Using Perturbed-Angular-Correlation Spectroscopy  
 Abstract    Perturbed-angular-correlation (PAC) spectroscopy was used to measure in ceramic samples of PbTi0 3 and BaTi0 3 the temperature dependence of the Ti-site electric-field gradients (EFGs) at temperatures very close to the ferroelectric-to-paraelectric transition temperatures T c . The samples were doped with small amounts of Hf that carried the 181 Hf — l8l Ta probe radioactivity. A high-frequency nuclear quadrupole interaction that decreases very little as the temperature approaches T c , characterizes the PbTi0 3 transition. The tetragonal and cubic phases for PbTi0 3 appear to coexist over a temperature interval of 8 ± 1 K, and the transition shows a thermal hysteresis of about 4 K. In contrast, a lower-frequency interaction that decreases rapidly as temperature approaches T c , characterizes the BaTiO, transition. Both phases of BaTi0 3 appear to coexist over an interval of about 2 K, and the thermal hysteresis is about 1 K. At temperatures above T c , both PbTi0 3 and BaTi0 3 show weak, non-vanishing Ti-site EFGs. Although, for BaTi0 3 , this effect limits the accuracy with which critical effects can be measured, we estimate a power-law exponent ß = 0.21 ± 0.05, which most likely is somewhat lower in magnitude than the actual critical exponent. For the explanation of our observations we assume the existence of a distribution of T c -values. This distribution would arise because the crystals could have spatially non-uniform distributions of nucleation sites, which for PbTi0 3 and BaTi0 3 could be point defects. 
  Reference    Z. Naturforsch. 51a, 411—421 (1996); received November 20 1995 
  Published    1996 
  Keywords    Ferroelectric, perovskite, nuclear electric-quadrupole, perturbed-angular-correlations, phase transition 
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 TEI-XML for    default:Reihe_A/51/ZNA-1996-51a-0411.pdf 
 Identifier    ZNA-1996-51a-0411 
 Volume    51