CHENG Shufeng ¹, CHEN Sheng ¹, MIAO Likun ¹, XIANG Zhengfei ², DENG Tengfei ²

(1. Wuhan Huanghelou Flavor & Fragrance 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) thermistors, characterized by their resistance decreasing with increasing temperature, are widely used in various fields, due to their high sensitivity, thermal stability and cost-effectiveness. Among these, the Y-Cr-Mn-O system perovskite NTC ceramics have been recognized for their precision and heat resistance, making them suitable for high-temperature exhaust gas detection systems. However, achieving consistency in electrical properties during industrial production of Y₂O₃-YCr_0.5Mn_0.5O₃ ceramics remains challenging, significantly affecting yield rates. This study is aimed to study the effects of densification, conductive phase particle size and dispersant on the consistency of electrical properties of the Y₂O₃-YCr_0.5Mn_0.5O₃ ceramics.[Methods] A two-step sintering method was employed to prepare 0.6Y₂O₃-0.4YCr_0.5Mn_0.5O₃ composite NTC ceramics. The initial step involved mixing raw materials, including Y₂O₃, Cr₂O₃, and Mn₃O₄, followed by ball milling and subsequent calcination to obtain YCr_0.5Mn_0.5O₃ powder. In the second stage, the powder was mixed with Y₂O₃ and other additives before being pressed into pellets and sintered at high temperatures. Various factors influencing consistency were examined, such as densification through Zr⁴⁺/Ca²⁺ co-doping, reduction of conductive phase particle size by re-milling and the application of different dispersants [(NH₄)₂SO₄, C₆H₁₁NO₇, Sago 9080]. Consistency was evaluated based on the distribution of resistances measured from cut samples, using statistical methods to quantify how closely the resistance values clustered around the mean.[Results] It is indicated that improving densification via Zr⁴⁺/Ca2⁺ co-doping could enhance consistency by 5%–15%, as compared with the single Ca²⁺ doping. Reducing the particle size of the conductive phase YCr_0.5Mn_0.5O₃ and ensuring uniform distribution contributed to higher consistency as well. Furthermore, the introduction of ammonium sulfate and ammonium citrate dispersants facilitated a more homogeneous dispersion of Y₂O₃ and YCr_0.5Mn_0.5O₃, thereby enhancing overall consistency. Notably, among the tested dispersants, ammonium citrate showed superior performance, achieving highest level of consistency across different tolerance ranges.[Conclusions] It is demonstrated that several strategies can be employed to improve the consistency of electrical properties in Y₂O₃-YCr_0.5Mn_0.5O₃ NTC ceramics. Enhancing densification through Zr⁴⁺/Ca²⁺ co-doping, optimizing the particle size of the conductive phase and utilizing effective dispersants all contributed positively to achieving greater consistency. These findings provided valuable insights for improving industrial production processes, ultimately leading to higher yields and more reliable NTC ceramic products. Future work should focus on further refining these approaches and exploring additional methods to optimize the electrical properties of NTC ceramics for practical applications.

Key words: NTC ceramics; electrical properties; homogeneity