Doping Rare Earth Dependent Mechanical Strength Improvement on Reduction of Ceria Based Solid Electrolytes

抄録

The reduction strengthening of various rare earth-added ceria-based electrolytes was investigated. Sm³⁺, Gd³⁺ and Y³⁺ were selected as the dopants, and the dependence of the lattice constant and conductivity on the doping amount was investigated. The lattice constant changed linearly with the amount added. Only the addition of Y³⁺ decreased the lattice constant with the addition amount. This is probably because Y³⁺ has a slightly larger ionic radius than Ce⁴⁺, but is affected by the formation of oxygen vacancies. The ionic conductivity increased with the addition of rare earth elements, and showed the maximum value at 20 mol% addition due to the relationship between the increase in carrier concentration and the association of defects. It was found that the conductivity of the sample with Y³⁺ addition was lower than that of the others when the addition amount was the same. A 10-20% improvement in strength was observed when contact reduction was carried out at the composition showing the maximum conductivity. Formation of a surface compression layer due to contact reduction was confirmed by a hardness test with different indentation depths. In addition, XPS confirmed that there is a concentration gradient of Ce³⁺ from the inside to the surface in the reinforced sample, suggesting that the formation of the compressive layer is due to the reduction expansion only on the surface. Depth profile of XPS and TG-MS showed that only Gd added ceria is difficult to be reduced, which is considered to be related to strength optimization temperature.