TAN Jian ¹, CAI Bing ¹, TANG Liangying ¹, WU Cong ¹, HUANG Ting ¹,

LIU Huachen ¹, XIANG Zhengfei ², DENG Tengfei ²

(1. China Tobacco Hubei Industrial Co., Ltd., Wuhan 430040, Hubei, China; 2. State Key Laboratory of Silicate

Materials for Architectures, Wuhan University of Technology, Wuhan 430070, Hubei, China)

Extended abstract:[Background and purposes] Negative temperature coefficient (NTC) thermosensitive ceramics are critical for temperature sensing applications, whereas their high resistivity in systems like Y₂O₃-YCr_0.5Mn_0.5O₃ limits practical use. Although prior doping with Zr⁴⁺ enhanced densification, the resistivity was further increased, deviating from the desired scale of kΩ·cm. Adjusting the phase ratio offered limited resistivity control and compromised thermal stability. This study was aimed to explore co-doping with alkaline earth ions to synergistically optimize resistivity, B-value and aging stability of Zr⁴⁺-modified 0.6Y₂O₃-0.4YCr_0.5Mn_0.5O₃ ceramics.[Methods] The samples were prepared by using a two-step sintering process at 1600 ℃. A baseline group (A0) was co-doped with 4–8 mol% CaO (A1–A3) or MgO (A11–A13). Phase composition was analyzed by using XRD, elemental distribution and valence states were characterized by using SEM-EDS and XPS. Electrical properties were measured after electrode coating. Aging resistance was evaluated by resistance drift (%) after 800 h at 300 ℃.[Results] All samples retained dual-phase structures. Ca²⁺/Mg²⁺ dissolved primarily in the perovskite phase, forming a dense "sea-island" microstructure. Ca²⁺ doping drastically reduced resistivity. At 8 mol%, the room-temperature resistivity (ρ) decreased by approximately 82% compared to the undoped sample (A0), while the B-value remained in the range of 2500-3000 K. In contrast, with 4 mol% Mg²⁺ doping, ρ was lowered to 5.14×104 Ω·cm, accompanied by higher B-values of 3300-3500 K. XPS revealed that the Mn⁴⁺/Mn³⁺ and Cr⁴⁺/Cr³⁺ ratios increased after doping, which was attributed to charge compensation: Ca²⁺ substitution at Y³⁺ sites generated holes and enhanced small-polaron hopping. Mg²⁺ likely enabled partial B-site substitution, weakening its impact. Aging tests showed that doping with Ca²⁺/Mg²⁺ increased the resistance drift; however, the presence of Zr⁴⁺ suppressed the drift by 1-2% through densification and grain refinement, thereby impeding cation vacancy migration.[Conclusions] The doping with Ca²⁺ effectively reduced the resistivity of Zr⁴⁺-modified NTC ceramics through charge compensation and enhanced polaron hopping, while maintaining a low B-value for wide temperature applicability. Mg²⁺'s inferior performance stemmed from possible B-site substitution and limited vacancy generation. Crucially, Zr⁴⁺ mitigated the negative aging effects of Ca²⁺/Mg²⁺ by improving microstructural stability. The Ca²⁺/Zr⁴⁺ co-doping strategy achieved balanced electrical properties and reliability, demonstrating significant potential for the development of industrial NTC thermistors.

Key words: NTC thermosensitive ceramics; YCr_0.5Mn_0.5O₃; Ca²⁺/Mg²⁺ doping; resistivity control