The Na-β″-Al
2O
3 electrolyte possessing high sodium ion conductivity is a candidate material for secondary batteries and thereto-electric converters. Sintered compacts of β″-Al
2O
3 containing 0-10vol% of ZrO
2 were made from calcined powder consisting of β″-Al
2O
3 and β-Al
2O
3. The effects of the ZrO
2 addition on the normalized index
f(β″) and microstructure of the sintered compacts were investigate, and the improvement of the density and normalized index was observed. It is therefore suggested that the ZrO
2 addition to β″-Al
2O
3 accelerates diffusion of the materials. The small amount of ZrO
2 is dissolved into the liquid which is generated during heat treatment. The dissolution ability or surface tension of that liquid appears to be influenced by the dissolution of ZrO
2, leading to improved sintering characteristics. The addition of ZrO
2 affects the microstructure, especially the grain growth of Al
2O
3. While abnormal grain growth of Al
2O
3 takes place in the case of 0.1vol% of ZrO
2 addition, such abnormal grain growth is prevented by a 1vol% of ZrO
2 addition. The concentration of Zr at the grain boundary, which decreases grain boundary mobility, was observed. The concentration of Zr is therefore considered to prevent abnormal grain growth.
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