抄録
The phase transition of high oxide-ion conductor Bi2(V1−xMEx)O5.5+δ (ME=Li and Ag, x=0.05 and 0.1) and its long-term phase stability against thermal decomposition have been studied. The transition behavior was determined by differential scanning calorimetry (DSC) as well as high-temperature X-ray diffraction (HT-XRD) analysis. The observed thermal and structural changes during temperature scans reveal the temperature dependence of electrical conductivity. Li- and Ag-doping do not sufficiently suppress thermal decomposition at intermediate temperatures between 400 and 600°C. In particular, partial decomposition was detected in Bi2(V0.9Ag0.1)O5.3 during a temperature scan by HT-XRD analysis, which explains the distinct change in electrical conductivity. We have generated pseudo-binary phase diagrams for Bi2(V1−xMEx)O5.5+δ based on the X-ray diffraction analysis of powders annealed for 200 h and differential thermal analysis. The thermodynamically stable region of Bi2(V1−xMEx)O5.5+δ is not sufficiently expanded by Li- and Ag-doping. At around 500°C, Bi2(V1−xMEx)O5.5+δ is metastable, although it shows the highest oxide-ion conductivity among solid oxides.
