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2000 (1)
1989 (2)
1Author    G. Chiodelli, V. Campari-Viganò, G. Massarotti, FlorRequires cookie*
 Abstract    The electrical behaviour of La2_JtSrJ.Cu04_v solid solutions (with x = 0, x = 0.025, x = 0.05, and x = 0.15) at temperatures between 10 and 900 K and under different oxygen partial pressure pQl — 1 -M0~6 atm) has been investigated. The samples prepared and measured under an 0 2 flux (i.e~, with y = 0) show a superconducting transition with Tc = 46, 29. 37 K for x = 0. 0.05 and"0.15, respectively. The samples with x = 0.025, y = 0, and x = 0, y = t= 0 exhibit no sign of superconductivity. In the temperature range 100-900 K. La2Cu04 is semiconducting, whereas the electrical resistivity is independent of temperature for the x =0.025 sample, and the x = 0.05 and x = 0.15 are metallic. 
  Reference    Z. Naturforsch. 44a, 26—28 (1989); received September 19 1988 
  Published    1989 
  Keywords    Superconductors, electrical properties, defects 
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 TEI-XML for    default:Reihe_A/44/ZNA-1989-44a-0026.pdf 
 Identifier    ZNA-1989-44a-0026 
 Volume    44 
2Author    G. Chiodelli, G. Campari-Viganò, G. FlorRequires cookie*
 Title    Y B a 2C  
 Abstract    u 30 7 _ x : T r a n s p o r t P r o p e r tie s an d D e fe c ts a t H ig h T e m p e r a tu r e Electrical resistivity measurements were carried out on polycrystalline YBa2Cu,07_ v at temper­ atures 300 < T < 1023 K and oxygen partial pressures 5 ■ 10"7 < p0l < 1 atm. The samples, equili­ brated in the range from 5 10~4 to 1 atm, show metallic behaviour, the one equilibrated at p0, = 2 • 10"5 shows a transition between metallic and semiconducting behaviour at 920 K, and that equilibrated at p0i — 5-10" shows semiconducting behaviour: for the latter the relevant resistivity is due to the oxygen-ion migration. The isotherms log a vs. log (in the temperature range from 723 to 1023 K) show slopes of about 1/6 at 723 K (orthorhombic phase) and about 1/2 at 1023 K (tetragonal phase). These results are discussed in terms of appropriate defect models. 
  Reference    Z. Naturforsch. 44a, 1167—1171 (1989); received September 28 1989 
  Published    1989 
  Keywords    Superconductors, electrical properties, defects 
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 TEI-XML for    default:Reihe_A/44/ZNA-1989-44a-1167.pdf 
 Identifier    ZNA-1989-44a-1167 
 Volume    44 
3Author    R. E. Alonso, A. López-GarcíaRequires cookie*
 Title    Charge Distribution Model in Cubic Perovskite-type Compounds  
 Abstract    A non-zero electric field gradient tensor, detected by probes that occupy sites with cubic point group symmetry, was observed in many AB0 3 perovskite-type compounds. This breakdown of local cubic symmetry is commonly associated with the presence of oxygen vacancies around the probe. This effect in BaT^Hfi-^O-, with x = 0.7, 0.5, 0.3, 0.1, 0.05 and 0.01 is studied in this work. The cell parameters were obtained at laboratory temperature using XRD spectroscopy. The hyperfine parameters were measured at a 1X1 Ta probe in the B site using Perturbed Angular Correla-tions (PAC) spectroscopy as a function of both temperature and composition. As a common trend, a static asymmetric and distributed quadrupolar interaction, strongly dependent on composition has been observed. The results, together with those corresponding to 1 > x > 0.75, are analyzed using the point-charge model in terms of polarized oxygen vacancies, different covalence of the Ti-0 and Hf-0 bonds with computational simulation for the lattice positions of cations and oxygen vacancies. 
  Reference    Z. Naturforsch. 55a, 261—266 (2000); received August 25 1999 
  Published    2000 
  Keywords    Perovskites, Ferroelectrics Materials, Defects, Polarized Oxygen Vacancies, Electric Field Gardient 
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 TEI-XML for    default:Reihe_A/55/ZNA-2000-55a-0261.pdf 
 Identifier    ZNA-2000-55a-0261 
 Volume    55