Negative Temperature Coefficient Thermistor Ceramics Research Articles

Sintering and electrical properties of Mn–Co–Fe–Zn–Ni–O high-entropy ceramics for NTC thermistors

In this work, the dual-phase structure Mn–Co–Fe–Zn–Ni–O high-entropy negative temperature coefficient (NTC) ceramics were synthesized by a solid-phase reaction method. The ceramics are mainly composed of the cubic spinel phase and the rock salt phase. Electron microscopic images revealed the typical morphology and the homogeneous distribution of all elements. The results confirmed that the microstructure and electrical properties of the high-entropy ceramics are closely related to the sintering temperature. As the sintering temperature increased, the content of the rock salt phase gradually improved, meanwhile, the higher resistivity of samples was achieved. Notably, it was found that an appropriate proportion of the rock salt phase could significantly enhance the aging stability of ceramics. The aging drift of the samples sintered at 1175 °C was only 0.632 %. In addition, the ratio of the two phases was adjusted by adding NiO. The ρ25 and B25/50 of the materials can be tuned in the range of 22.25 kΩ cm∼24.19 kΩ cm and 4047 K–4145 K, respectively. Regulating the phase ratio of dual-phase materials is a novel strategy for designing NTC ceramic materials with excellent characteristics. This work provides an idea for future research on high-entropy NTC thermistor ceramics.

Fabrication of high-sensitivity Bi0.2-xCexSr0.5La0.3TiO3 (0

High density negative temperature coefficient (NTC) thermistor ceramics Bi0.2-xCexSr0.5La0.3TiO3 (0 < x < 0.05) (BCSLTO) were synthesized by the Pechini method. This work is the first to characterization analysis the excellent NTC characteristics of BCSLTO ceramics at high temperatures. BCSLTO NTC thermistor ceramics have wide operating temperature is 300 °C-1000 °C, and mild sintering conditions with the conventional sintering at 1250 °C. The important electrical performance parameters of BCSLTO ceramics are as follows: the resistivities at 300 °C, 700 °C, and 1000 °C are 3.26 × 109–8.99 × 107 Ω cm, 2.21 × 105–1.05 × 105 Ω cm, and 1.18 × 103–1.13 × 103 Ω cm, respectively; the thermal constant B300/700 is 13385.9–9408.8 K; the activity energy Ea300/700 is 1.15–0.81 eV. The resistivity and the thermal constant B can be widely control by doping Ce. In addition, the resistivity drift improves as the Ce doping content increases (below 5%). The new high-temperature Bi0.2-xCexSr0.5La0.3TiO3 ceramic materials with mild sintering conditions, wide operating temperature and high-temperature stability can be used as potential candidates for high temperatures and harsh environments.

Core–shell NTC materials with low thermal constant and high resistivity for wide‐temperature thermistor ceramics

AbstractCore–shell structures have been proposed to improve the electrical properties of negative‐temperature coefficient (NTC) thermistor ceramics. In this work, Al2O3‐modified Co1.5Mn1.2Ni0.3O4 NTC thermistor ceramics with adjustable electrical properties were prepared through citrate‐chelation followed by conventional sintering. Co1.5Mn1.2Ni0.3O4 powder was coated with a thin Al2O3 shell layer to form a core–shell structure. Resistivity (ρ) increased rapidly with increasing thickness of the Al2O3 layer, and the thermal constant (B) varied moderately between 3706 and 3846 K. In particular, Co1.5Mn1.2Ni0.3O4@Al2O3 ceramic with 0.08 wt% Al2O3 showed the increase of ρ double, and the change in its B was less than 140 K. The Co1.5Mn1.2Ni0.3O4@Al2O3 NTC ceramics showed high stability, and their grain size was relatively uniform due to the protection offered by the shell. The aging coefficient of the ceramic was less than 0.2% after aging for 500 hours at 125°C. Taken together, the results indicate that as‐prepared Co1.5Mn1.2Ni0.3O4@Al2O3 NTC ceramics with a core–shell structure may be promising candidates for application as wide‐temperature NTC thermistor ceramics.

Effect of Y Substitution on Electrical Properties of Yn(Ba0.8Bi0.2)1–nFe0.9Sn0.1O3 Negative Temperature Coefficient Thermistor Ceramics

Effect of Y Substitution on Electrical Properties of Yn(Ba0.8Bi0.2)1–nFe0.9Sn0.1O3 Negative Temperature Coefficient Thermistor Ceramics

New negative temperature coefficient thermistor ceramics in Mn-doped CaCu3−xMnxTi4O12 (0≤x≤1) system

New negative temperature coefficient (NTC) ceramics based on CaCu3−xMnxTi4O12 (0≤x≤1) compositions have been investigated. The grain size of the CaCu3−xMnxTi4O12 samples decreases at first and then increases with increasing Mn content. The X-ray photoelectron spectroscopy analysis corroborates the presence of Mn3+ and Mn4+ in Mn-doped samples, which results in a decrease in the activation energy. All the NTC thermistors prepared show a linear relationship between the natural logarithm of the resistivity and the reciprocal temperature, indicative of NTC characteristics. The Mn-doped CaCu3−xMnxTi4O12 NTC thermistors provide various electrical properties, depending on Mn content. The values of ρ25, B constant and activation energy of the NTC thermistors are in the range of 2.22×106–3.22×108Ωcm, 5488–8031K, and 0.473–0.692eV, respectively.

Material Design for High Strength NTC Thermistor Ceramics

Various factors were investigated to decide the mechanical properties of (Mn1–xNix)3O4 ceramics, that are typical composition systems of NTC (negative temperature coefficient) thermistors. The strength of NTC thermistor ceramics can be improved by designing the material so that the compressive stress may remain at the surface of the ceramics. At high temperature, the thermal expansion coefficient of a rock salt phase segregated internally ceramic increases over that of the spinel phase, further, on the surface of the ceramics, this compressive stress remains below room temperature. Moreover, it was confirmed that the stress analysis result by the FEM corresponded well with the stress measurement result on the surface of the ceramics measured by μ -XRD.