ORDRE, DÉSORDRE ET STOECHIOMÉTRIE DANS LES COMPOSÉS DE TYPE ALUMINE βReportar como inadecuado




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Abstract : The group of two-dimensional superionic conductors is mainly constituted by a set of compounds with an hexagonal structure of β alumina type 11 Al2O3-B2O. The exceptional electrical properties are due to the high mobility of B+ ions Na+, Ag+, K+, T1+, NH+4, H3O+ in the loose packed planes of the structure. Classical processes crystal growth, solid state reaction provide a non-stoichiometric compounds for which the formula may be expressed by : 11 Al2O3-1 + x B2O with 0.3 ⩽ x ⩽ 1 X Ray diffraction approach shows a noticeable two-dimensional disorder. A Frenkel defect is also detected in the spinel blocks located between the conducting planes. Diffuse scattering and Raman diffusion give data on the local ordering as a function of the temperature and give evidence of two-dimensional ordered microdomains. By heating non stoichiometric NH+4 β alumina and ion exchanging in molten salts, we are able to prepare compounds in which the composition is quasi stoichiometric x = 0. A structural investigation of these phases shows an ordering within the blocks Frenkel defects are no longer found and in the conducting planes superstructure with long range ordering.





Autor: Ph. Colomban J. Boilot A. Kahn J. Thery G. Lucazeau R. Mercier G. Collin R. Comes

Fuente: https://hal.archives-ouvertes.fr/



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