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.)