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1997 (1)
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1Author    O. Wegener3, R. K. Üchler3, A. W. AtterichbRequires cookie*
 Abstract    12STe nuclear spin relaxation (NSR) and electrical conductivity measurements were performed on ultrapure single-crystalline paratellurite (a -T e0 2) between about 50 K and the melting point (1007 K) at various oxygen partial pressures (1 b a r -10"4 bar). At elevated temperatures the NSR rate l / 7 \ and conductivity a are caused by the diffusive motion o f point defects. From the observed p02-dependence of 1/Ti and a a defect model is developed which is shown to be consistent with the experimental data. The m odel involves ionic oxygen interstitials (O"), doubly charged oxygen vacancies (Vo') and charge-com pensating electron holes (h'). The observed pressure dependence suggests that the N SR rate is induced by the m otion of \ q while the conductivity is due to the m obility o f h*. Evaluation o f the data leads to 3.3 eV for the incorporation enthalpy o f oxygen on interstitial sites and to 4.5 eV for the formation enthalpy of oxygen Frenkel pairs (O "-V q'). Further, the chemical diffusion coefficient Dc is found to be caused by the ambipolar diffusion o f OS' and h \ At 950 K we obtained from both the NSR and conductivity experiments D c = (1 ± 0.3) • 10" 5 cm 2/s. 
  Reference    Z. Naturforsch. 49a, 1151 (1994); received August 22 1994 
  Published    1994 
  Keywords    Oxides, Point defects, Diffusion, N M R, Conductivity 
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 TEI-XML for    default:Reihe_A/49/ZNA-1994-49a-1151.pdf 
 Identifier    ZNA-1994-49a-1151 
 Volume    49 
2Author    Giorgio Spinolo, Umberto Anselmi-Tamburini, Paolo GhignaRequires cookie*
 Title    An Exact and Simple Approach to log-log Plots for Defect and Ionic Equilibria  
 Abstract    An alternative approach to log-log plots for defect equilibria in the solid state and ionic equilibria in solution is presented. The method is based on the strictly monotone character of the functional dependence of an externally controlled thermodynamic variable (e.g. the oxygen partial pressure P(0 2) for the defect equilibria in a simple oxide, or a total concentration for the ionic equilibria in solution) on a chemically relevant compositional variable (such as the electron concentration n for defect equilibria, or [H 3 0 + ] or a free ligand concentration for solution equilibria). This functional dependency can be safely inverted. The concentration of all species and the externally controlled thermodynamic variable can be calculated as a function of the chemically relevant compositional variable. The appropriate plots are then obtained using naively a spreadsheet program. This method gives exact results in many more cases than the traditional approach. 
  Reference    Z. Naturforsch. 52a, 629—636 (1997); received June 19 1997 
  Published    1997 
  Keywords    Chemical equilibria, Point defects, log-log plots 
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 TEI-XML for    default:Reihe_A/52/ZNA-1997-52a-0629.pdf 
 Identifier    ZNA-1997-52a-0629 
 Volume    52 
3Author    V. Massarotti, D. Capsoni, A. Marini, V. Berbenni, G. Flor, C. MargheritisRequires cookie*
 Abstract    t r u c t u r a l a n d D e fe c t S tu d y o f N a j T -G a ll a te by X -R a y P o w d e r D iffra c tio n A n a ly s is The Rietveld profile refinement has been applied to X-ray powder diffraction data on Na/T-gallate, a solid electrolyte isostructural with Na/T-alumina and characterized by different types of lattice defect. Several structural models have been refined and discussed in order to understand if a statistical comparison of the structure discrepancy factors can be used as a reliable criterion to retain or reject structural changes from one model to the other. It is shown that, due to the correlation between structural parameters and to the poor sensitivity of the structure discrepancy factors to chemical composition, some care is necessary to direct correctly the refinement and to obtain a reliable structural model. 
  Reference    Z. Naturforsch. 46a, 321 (1991); received January 7 1991 
  Published    1991 
  Keywords    Powder diffraction Profile refinement, Na/T-gallate, Point defects, Solid electrolyte 
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 TEI-XML for    default:Reihe_A/46/ZNA-1991-46a-0321.pdf 
 Identifier    ZNA-1991-46a-0321 
 Volume    46