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1Author    G. C. Papavassiliou3, G.A M Ousdis3, C. P. Raptopouloub, A. TerzisbRequires cookie*
 Title    Some New Luminescent Compounds Based on 4-MethyIbenzylamine and Lead Halides  
 Abstract    Compounds of the general formula (CH3NH3)"_i(C H 3C6H4C H 2N H 3)2Pb"X3"+i, where X = I, Br, Cl and n= 1,2, 3,..., were prepared and characterized analytically and spectroscopically. Moreover, (CH3C6H4CH2NH3)2PbX4 and (C H ^ N H jX C ^ C e ^ C H z N H jh P b il? were charac­ terized by X-ray crystal structure analysis. Their optical absorption and photoluminescence spectra exhibit excitonic bands, even at room temperature. 
  Reference    Z. Naturforsch. 55b, 536—540 (2000); received March 6 2000 
  Published    2000 
  Keywords    Hybrides, Perovskites, Excitonic Spectra 
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 TEI-XML for    default:Reihe_B/55/ZNB-2000-55b-0536.pdf 
 Identifier    ZNB-2000-55b-0536 
 Volume    55 
2Author    G. C. Papavassilioua, G. A. Mousdisa, C. P. Raptopouloub, A. TerzisbRequires cookie*
 Title    Preparation and Characterization of [C6H5CH2 NH3]2PbI4, [C6H5CH2 CH2 SC(NH2 )2]3PbI5 and [C10H7CH2NH3]PbI3 Organic-Inorganic Hybrid Compounds  
 Abstract    The preparation, crystal structures, optical absorption spectra, and photoluminescence spectra of the title compounds are reported. The compounds were prepared in single crystal form. [CftHsCHiNH.^PbL consists of anionic perovskite sheets of corner-sharing Pbl6 octahedra, which alternate with the C ö H s C ^ N H ^ sheets. [ C ftH s C ^ C ^ S Q N H i^ b P b ls consists of zig-zag chains of anionic corner sharing Pbl6 octahedra separated by C6H5CH 2CH 2SC(NH2)2 cations. [CioH7CH 2N H 3]Pbl3 consists of twin chains of edge-sharing P b^ octahedra separated by C 10H7CH2NH3 cations. The compounds are thus low-dimensional systems. The excitonic spectra were observed in all cases, even at room temperature, and the possibility of organic-inorganic excitonic interactions is discussed. 
  Reference    Z. Naturforsch. 54b, 1405—1409 (1999); received July 7 1999 
  Published    1999 
  Keywords    Organic-Inorganic Hybrides, Perovskites, Low-Dimensional Compounds, Excitonic Spectra 
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 TEI-XML for    default:Reihe_B/54/ZNB-1999-54b-1405.pdf 
 Identifier    ZNB-1999-54b-1405 
 Volume    54 
3Author    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 
4Author    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 
5Author    Carsten Schinzer3, RiyadhA. Saym, HassanM. Asfour0Requires cookie*
 Title    Hydrogenation of Toluene over Lao.sSro^Fej.xCoxO^ Perovskite Catalysts  
 Abstract    The hydrogenation of toluene over perovskites of composition Lao.gSro.iFei-x Cox0 3 _ z (x = 0.0, 0.2, 0.5, 0.8 and 1.0) is reported. The catalyst material has been prepared by the coprecipitation method using maleic acid as the complexing agent. The activity for the gas phase reaction of toluene and hydrogen at temperatures between 50 °C to 300 °C is reported for as-prepared and activated materials. The conversion has been found to be nearly temperature-independent over the as-prepared per­ ovskites with a maximum o f 40% conversion found for a composition Lao.8Sro.2Feo.5Coo.5O 2.86-Activation by an oxygen treatment at 500 °C was successful to enhance the activity of the Co-rich perovskites. All of these catalysts show a complete conversion of toluene at 100 °C, but activity decreases by time due to a reduction of the catalyst material. Again, Lao.8Sro.2Feo.5Coo.5O2.86 exhibits the slowest loss of activity. A model for its special properties is mainly attributed to the p-type conduction behaviour. The conversion behaviour of the perovskite type catalysts investigated here is compared to the results obtained with noble-metal supported catalysts and it can be concluded, that the perovskites exhibit higher conversion rates, maximum temperatures and higher cracking onset temperatures than these. 
  Reference    Z. Naturforsch. 52b, 927—934 (1997); received April 11 1997 
  Published    1997 
  Keywords    Perovskites, Mixed Metal Oxides, Stability, Catalytic Hydrogenation, Catalytic Reduction 
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 TEI-XML for    default:Reihe_B/52/ZNB-1997-52b-0927.pdf 
 Identifier    ZNB-1997-52b-0927 
 Volume    52