Effect of rare earth oxides on the thermal stability of Mn-Fe-Co-Zn-O ceramics under high-temperature N2 atmosphere

The Mn-Fe-Co-Zn-O series is a widely used thermistor material, but its thermal stability is compromised by nitrogen glass encapsulation, limiting its application in electrical devices. To address this issue, La 2 O 3 and Y 2 O 3 were used as rare earth oxide dopants, and xR 2 O 3 -Mn 0.76 Fe 0.87 Co 1.07 Zn 0.3 O 4 (x = 0.0025, 0.005, 0.01, 0.02) negative temperature coefficient (NTC) materials were synthesized via solid-state sintering. The effect of rare earth doping on the electrical properties after high-temperature nitrogen annealing was investigated. After annealing at 750°C for 4 h, the variation in resistivity ( ρ 25 ) and material constant ( B 25/50 ) significantly decreases with increasing La doping. For the La-doped sample (x = 0.01), Δρ 25 decreased to 7.77% and ΔB 25/50 to 0.77% (for the Y-doped sample (x = 0.01), Δρ 25 decreased to 22.76% and ΔB 25/50 to 1.91%), compared to the undoped sample, where Δρ 25 reduced by 168.84% and ΔB 25/5 0 by 5.57%. This improvement was attributed to rare earth accumulation at grain boundaries, filling voids and forming R-O bonds, which inhibited oxygen vacancy migration and significantly reduced grain boundary resistance. Rare earth doping effectively improved the thermal stability and electrical consistency of NTC thermistor ceramics in high-temperature nitrogen atmospheres, offering a new strategy for high-temperature encapsulation applications. (Y-doped samples showed similar results, as detailed in the Supplementary Materials.)