Preparation, crystal structure and oxide ion conductivity of binary rare earth fluoride oxides

Abstract

Binary rare earth metal fluoride oxides, BMFOs containing neodymium, which were prepared by a solid-state reaction between NdF 3 and Ln 2O 3, were found to give a high oxide ion conductivity. The ionic conductivity was considered in connection to the crystal structure and the valency change of rare earth elements. All compounds of Nd 2Ln 2F 6O 3 give a tetragonal structure which resembled closely the fluorite structure. As an oxide ion conductible structure, the super-lattice consist of a oxygen plane and a fluorine plane can be supposed, and oxide ions can be considered to transport along the oxygen plane. Sm and Eu easily vary n the oxidation state from trivalent to divalent, on the other hand, those of Gd and Ce are settled. This results in reducing the Coulombic interaction between oxide ion and rare earth ion, and in increase the mobility of oxide ion. On table 1 some sample data are listed. 1 Summary of sample data Ln in E.C.(S/cm) O 2−T.No. Density Lattice const. Nd 2Ln 2F 6O 3 650°C 450°C 650°C a o C o(A) Y 1.3×10 −3 0.70 0.85 6.50 5.58 5.59 Ce 2.5×10 −3 0.15 0.25 5.91 5.70 5.74 Sm 2.3×10 −2 0.85 0.90 6.90 5.63 5.67 Eu 1.2×10 −2 0.90 0.90 7.27 5.63 5.64 Gd 7.9×10 −3 0.70 0.80 6.96 5.61 5.65