Studies on the Composition-Structure-Property Relations in Ceramic Grain-Boundaries

TEM observations of the grain boundary areas were made on semiconductng&lt；BaTiO_3&gt；Thick film.The 180 domains across the grain boundary could not be ovserved the possibility of the existence of 90 domains was suggested。Exsolution method was applied to the NiO-ZnO ceramics to control the microstructure in which the grain-boundary regions were rich in ZnO and the grains were NiO rich phase，as detected by XMA.The change in V-I characteristics with the change in relative humidity was measured at 25°c.&lt；Ni_(0.2)Zn_(0.8)O&gt；sintered at 1300°c and further annealed at 800°c for 336h was found to be the most sensitive to humidity.The electrical breakdown strength of single crystal MgO at1000-1400°c decreased with increase in the dislocation density and that of polycrystalline MgO indicated a significant effect of the grain boundaries.A high correlation between the ionic conductivity and the breakdown strength was found，which together with the observed melted track sugested that the electrolytic decomposition took place。The varistor properties were examined for porous ZnO containing no dopants such as&lt；Bi_2O_3&gt；or&lt；Pr_6O_(11)&gt；.Comparison of I-V curves for the oxidized and unoxidized samples indicated that oxygen，which had chemisorbed and diffused into the grain boundary，played a role in giving rise to varistor characteristics.

TEM observations of the grain boundary areas were made on semiconductng <BaTiO_3> Thick film. The 180 domains across the grain boundary could not be ovserved the possibility of the existence of 90 domains was suggested. Exsolution method was applied to the NiO-ZnO ceramics to control the microstructure in which the grain-boundary regions were rich in ZnO and the grains were NiO rich phase, as detected by XMA. The change in V-I characteristics with the change in relative humidity was measured at 25゜c. <Ni_(0.2)Zn_(0.8)O> sintered at 1300゜c and further annealed at 800゜c for 336h was found to be the most sensitive to humidity. The electrical breakdown strength of single crystal MgO at 1000-1400゜c decreased with increase in the dislocation density and that of polycrystalline MgO indicated a significant effect of the grain boundaries. A high correlation between the ionic conductivity and the breakdown strength was found, which together with the observed melted track suggested that the electrolytic decomposition took place. The varistor properties were examined for porous ZnO containing no dopants such as <Bi_2O_3> or <Pr_6O_(11)> . Comparison of I-V curves for the oxidized and unoxidized samples indicated that oxygen, which had chemisorbed and diffused into the grain boundary, played a role in giving rise to varistor characteristics.