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Research On The Property Of Ceria With The Empirical Electron Theory In Solid And Molecule

Posted on:2013-02-12Degree:MasterType:Thesis
Country:ChinaCandidate:D Q WuFull Text:PDF
GTID:2231330374498390Subject:Materials Physics and Chemistry
Abstract/Summary:PDF Full Text Request
Ceria or doped ceria having a good property of ionic conduction and catalysis in the temperature range from500℃to700℃is the key material of SOFC in the lower temperature field. In this paper, the valence electron structure of pure ceria, doped ceria with varied doping condition and (111) surface with different concentration of oxygen vacancies was calculated with the empirical electron theory in solid and molecule and the relationship between valence electron structure and macroscopic properties was discussed.The essential reason resulted in a high melting point of ceria is the high value of bond energy of the strongest covalent bond (88.06kJ/mol). The weak conductivity of pure ceria resulted from the low content of lattice electron and well-proportioned distribution of covalent bond and the catalysis of ceria were due to unpaired d electron in ceria.The effect of assembling covalent electron of dopant in the doped ceria was observed. This effect enlarged the difference of bond energy of covalent bond which formed by the O atoms near the dopant and resulted in non-uniform stress of these O atoms. The mobility of these O atoms enhanced with relatively low energy suggesting the improvement of ionic conductivity. A lower value of bond energy of weakest covalent bond led to a better property of ionic conductivity.Having the lowest value of surface energy among the crystal planes of ceria, (111)plane had the highest possibility of be the surface of ceria. The related Ce4+turned to Ce3+on the sub-surface of (111) when oxygen vacancies had formed on the (111) surface and the Ce3+demonstrated the effect of assembling covalent electron as the case in bulk. The value of bond energy of weakest covalent bond was affected by concentration of oxygen vacancies of surface. A higher concentration of oxygen vacancies of surface suggested a higher mobility of O atoms near the surface and less stability of the surface.
Keywords/Search Tags:the empirical electron theory in solid and molecule, ceria, valence electron structure, dopant, surface, bond energy
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