Synergistically enhancing the conductivity and electrical stability of negative-temperature-coefficient Co0.98Mn2.02O4 ceramics by codoping Cu/ Ni at the A/B site

Negative-temperature-coefficient (NTC) ceramics, known for their high sensitivity, accuracy, and costeffectiveness, have consistently garnered notable research attention. Despite their advantages, challenges persist in developing low-resistivity and highly stable NTC ceramics for inrush current suppression and lowtemperature measurements. Herein, CuxCo0.98_ xNiyMn2.02_yO4 ceramics codoped with Cu and Ni are synthesized using a solid-state coordination reaction. The ceramics exclusively doped with Cu comprise tetragonal and cubic spinel phases, and cubic-phase content increases with increasing Cu content. In the codoped Cu0.2Co0.78NiyMn2.02_yO4 ceramics, the cubic-phase content increases with increasing of Ni content when y <= 0.3. They exhibit a single cubic spinel phase at y = 0.4, whereas a (Mn/Co/Ni/Cu)O rock-salt phase precipitates at y = 0.5. Moreover, Cu-Ni codoping can promote grain growth, and the precipitated rock-salt phase hinders grain growth. Compared with the ceramics exclusively doped with Cu, the Cu-Ni-codoped ceramics exhibit lower roomtemperature resistivity (rho 25) and aging values. The rho 25, material constant, and aging values of the ceramics exclusively doped with Cu are 370.9-6329.6 Omega cm, 3079-4084 K, and 2.84%-17.2 %, whereas those of the Cu-Ni-codoped ceramics are 28.0-137.2 Omega cm, 3056-3222 K, and 2.34%-3.02 %, respectively. The optimized ceramics, Cu0.2Co0.78Ni0.4Mn1.62O4 and Cu0.2Co0.78Ni0.5Mn1.52O4, show promise for use in inrush current suppression and low-temperature measurement devices, with low rho 25 (28.0 and 38.8 Omega cm, respectively) and aging (2.65 % and 2.38 %, respectively) values. The study also comprehensively explores the effects of Cu-Ni codoping on microstructure defects and valence states, presenting a straightforward approach for developing NTC ceramics with low resistivity and high stability.