Core-shell structures have been proposed to improve the electrical properties of negative-temperature coefficient (NTC) thermistor ceramics. In this work, Al 2 O 3 -modified Co 1.5 Mn 1.2 Ni 0.3 O 4 NTC thermistor ceramics with adjustable electrical properties were prepared through citrate-chelation followed by conventional sintering. Co 1.5 Mn 1.2 Ni 0.3 O 4 powder was coated with a thin Al 2 O 3 shell layer to form a coreshell structure. Resistivity (ρ) increased rapidly with increasing thickness of the Al 2 O 3 layer, and the thermal constant (B) varied moderately between 3706 and 3846 K. In particular, Co 1.5 Mn 1.2 Ni 0.3 O 4 @Al 2 O 3 ceramic with 0.08 wt% Al 2 O 3 showed the increase of ρ double, and the change in its B was less than 140 K. The Co 1.5 Mn 1.2 Ni 0.3 O 4 @Al 2 O 3 NTC ceramics showed high stability, and their grain size was relatively uniform due to the protection offered by the shell. The aging coefficient of the ceramic was less than 0.2% after aging for 500 hours at 125°C. Taken together, the results indicate that as-prepared Co 1.5 Mn 1.2 Ni 0.3 O 4 @Al 2 O 3 NTC ceramics with a core-shell structure may be promising candidates for application as widetemperature NTC thermistor ceramics. K E Y W O R D S ceramic matrix composites, core-shell structures, electrical properties, NTC thermistors 4394 | LIU et aL.

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