TEM and electrical properties characterizations of Co0.98Mn2.02O4 NTC ceramic

Abstract

Spinel-type Co0.98Mn2.02O4 negative temperature coefficient (NTC) ceramics were prepared by the solid-state coordination reaction and the influence of sintering temperature on their microstructure and electrical properties are discussed. Because of the phase transformation at high temperatures, the sintered ceramics consist of both tetragonal and cubic spinel phases. Twins defects are observed in all of the prepared ceramics. The grain size and the twin width increase with increasing sintering temperature. The twin type changes from lamellae (L) to large lamellae (LIT) as the sintering temperature increased from 1200 to 1250 °C. The coherent twin interface planes are parallel to the (112) plane. When the sample was sintered at 1250 °C, the twin planes are (112), (1¯12)M and (1¯12)T. The room-temperature resistivity decreases with the increase in sintering temperature, because of the increase in grain size and twin width.