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2000 (1)
1998 (1)
1Author    J.Mestnik Filho, A. W. Carbonari, E. F. Motta, M. Moralles, R. N. Saxena, M. Olzon-Dionysio, S. D. De SouzaRequires cookie*
 Title    Ionic Size Induced Defects in Lead Titanate-Zirconate Perovskite Studied by TDPAC Method  
 Abstract    Time differential perturbed angular correlation (TDPAC) measurements were carried-out on PbZr 0 8 Ti 0 2 0 3 as a function of temperature. A broad distribution of electric field gradient (EFG) was observed in all cases with a second site for 181 Hf-181 Ta probes in the R3c phase. The results were analyzed in terms of a model which simulates an attraction of the ions by the smaller Ti ions. The EFG was calculated within the point charge approximation, by averaging over a large number of configurations generated by random distribution of the Ti ions in an ensemble of lattice cells. It was verified that the model reproduces qualitatively the broadening of the TDPAC frequencies as well as explains the second component EFG observed experimentally. 
  Reference    Z. Naturforsch. 53a, 318—322 (1998); received October 31 1997 
  Published    1998 
  Keywords    PbZr x Ti 1^3, Perovskites, Crystal Defects, TDPAC Measurements 
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 TEI-XML for    default:Reihe_A/53/ZNA-1998-53a-0318.pdf 
 Identifier    ZNA-1998-53a-0318 
 Volume    53 
2Author    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