||Bi2O3-based materials with various oxide dopants had the potential being used as electrolyte layer for intermediate temperature solid oxide fuel cells (IT-SOFCs). Recent investigations reported that doped-Bi2O3 might produce complex phase transformations during cooling to degrade it ionic conductivity. In order to stabilize the high temperature phase (δ-phase or cubic phase) in room temperature, many reports had addressed the possible routes to maintain the conductivity properties in a temperature range. For example, the addition of various alio-valent cationic dopants, such as TiO2, SnO2, ZrO2, TeO2 and Nb2O5. We focused on M-doped Bi2O3 materials of SOFCs to study the effects of material properties and structure stability in this research, and it divided into two subjects: (1) Bi2O3-TiO2 system and (2) Bi2O3-TiO2-V2O5 system.
In Bi2O3-TiO2 system, we prepared three TiO2-doped Bi2O3 bulky samples by colloidal process. The suspensions of mixtures are dispersed to the best condition, and pressure filtration (See P.33, 2.5). The samples are sintered at 725 to 850 °C for 2 hrs in air and show uniform and dense microstructures. Materials characteristics of the electrolytes are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM). Electrical behaviors were measured by AC impedance and DC conductivity in the range of 400~700 °C in air. The results show that 14.3 mol%-TiO2 doped Bi2O3 (14BTO) samples shows single phase (Bi12TiO20) and relatively high density ( > 95.0% T.D.). As III
sintering at 800 °C for 2 hrs, the highest total conductivities were obtained in 5BTO with σ700℃=1.12×10-3 Scm-1, but the result was still lower than YSZ. Therefore, we kept adding V2O5 to improve the conductivity of Bi2O3-TiO2 system. Finally, we also researched the effect of material stability and the aging time of this system to study if the structure and conductivity would decline.