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The existing and distributing states of crystal phases in the nonohmic zinc oxide ceramics with five additives, 0.5Bi2O3, 1.0Sb2O3, 0.5Co2O3, 0.5MnO2 and 0.5Cr2O3 (mol.%) were investigated by using various analytical techniques. The ceramics consist of the ZnO and spinel phases and mixed phases of β-and δ-Bi2O3. The ZnO phase corresponds to the main constituent grains, which are single crystals 10 to 20 microns in size with a twinning structure and randomly orientated. The spinel phase corresponds to single crystal grains a few microns in size, which are discontinuously located along comparatively wide grain boundaries. The Bi2O3 phases correspond to continuously spreading intergranular layers, which separate the ZnO grains from each other. The width of the interanular layers in the narrow grain boundaries between two adjacent ZnO grains is less than 500 Å.
Masanori Inada (Sat,) studied this question.