Sintering temperature–induced evolutions of crystal structure, microstructure, twin defects, and electrical properties of Co0.98Cu0.4Mn1.62O4 ceramics

In this study, Co 0.98 Cu 0.4 Mn 1.62 O 4 ceramics with dual phases and twin defects were successfully prepared by the thermal decomposition of oxalate precursors. The effects of sintering temperature on the phase composition, microstructure, and electrical properties of Co 0.98 Cu 0.4 Mn 1.62 O 4 ceramics were investigated. X-ray diffraction results show that the ceramics are composed of cubic and tetragonal spinel phases and the content of the cubic spinel phase increases with increasing sintering temperature. Scanning electron microscopy images revealed that the grain size increases with increasing sintering temperature and the bulk density first increases and then decreases. Transmission electron microscopy results revealed a change in the twin configuration from needle-shaped twins to lamella without internal twins and finally to lamella with internal twins with increasing sintering temperature. X-ray photoelectron spectroscopy results showed that an increase in the sintering temperature causes the oxidation of Cu + to Cu 2+ , and the average valence state of Mn ions to first increase and then decrease. However, during the aging process, Cu + did not oxidize to Cu 2+ and the Cu + content increased. Co 0.98 Cu 0.4 Mn 1.62 O 4 ceramics sintered in the temperature range of 1000°C–1200°C exhibited excellent electrical properties. The resistivity ( ρ 25 ), material constant ( B 25/85 ), and aging values were 17.6–106.66 Ω·cm, 2836–3338 K, and 1.63%–3.41%, respectively. Herein, the relationships among the microstructures, valence states, and electrical properties are also discussed in detail.