Formation Region of Monophase with Cubic SpineL-type Structure in Mn-Fe-Ni Ternary System and Electrical Properties of Sintered-bodies Prepared from the Region

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First object of this study is to define the composition area of cubic spinel-type monophase oxide composed of Mn-Fe-Ni ternary system. The second is to investigate the preparation method for sintered bodies consisting of monophase with cubic spinel-type structure. The third is to evaluate the electrical properties of the sintered bodies. The region to be cubic spinel monophase at 1000℃ was recognized to be near on the line connecting the points of Mn:Fe:Ni=2.25:0:0.75 and 0.5:1.5:1. The bodies, in which a couple of oxides different from the crystal structure were contained, heated at 1400℃ for sintering were confirmed to be converted to monophase cubic spinel-type oxides by heat treatment at 1000℃ for 48 h in air. The electrical conductivities increased exponentially with increasing temperature, indicating that these oxides have intrinsic NTC thermistor characteristics. The electrical properties of the oxides were evaluated to be more stable compared to one on the market in measurement at 700℃ in nitrogen. It was concluded from the mobility and its temperature dependence that the electrical conduction is based on the small polaron hopping mechanism.