| Budget Amount *help |
¥1,800,000 (Direct Cost: ¥1,800,000)
Fiscal Year 1992: ¥400,000 (Direct Cost: ¥400,000)
Fiscal Year 1991: ¥1,400,000 (Direct Cost: ¥1,400,000)
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| Research Abstract |
The oxide ion conductivity for binary rare earth metal fluoride oxides containing neodymium has been considered in connection to the crystal structure and the valence change of rare earth elements. All compounds of Nd_2Ln_2O_3F_6 give a tetragonal structure which resembles closely the fluorite structure. As an oxide ion conductione structure, the super-lattice consists of an oxygen plane and a fluorine plane can be supposed,and oxide ions can transport along the oxygen plane. Sm and Eu easily change in the oxidation state from trivalent to divalent. This results in reducing the Coulombic inter-action between oxide ion and rare earth ion, and in increase the mobility of oxide ion. The hot-press was tried to get high dense sintered samples. Under the condition up to 1200ﾟC and 250kg/cm^2 the geometrical density was up to 85% of theoretical one. To get high dense sintered sample, the control of the particle size distribution of a powdered sample and the vacuum hot-press were found to be effective.
CeO_2, Nd_2O_3, Sm_2O_3 and Eu_2O_3 begin to react with F_2 gas at 260ﾟC, and are completely converted into trifluoride up to 550ﾟC. The neodymium oxide fluoride with the minimum fluorine composition is found to be NdOF and the fluorine-rich compositions is expressed by Nd_4O_<6-x>F_<2x>, where 2<x<6. In this reaction the free oxide ions substituted by fluoride ions are assumed to be not able to migrate in a fluoride layer formed on the oxide particle surface. In the reaction between CeO_2 and F_2 gas, it is found that fluorine was incorporated into the crystal lattice of CeO_2 without change of structure and oxidation state of Ce(+4) below 270ﾟC, and the valence Ce(+4) drastically changes to Ce(+3) with evolution of oxygen at 270-290ﾟC.
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