Ma Panfei,Zhang Huimin,Chen Mingxing,Liu Ting,Chang Aimin,Su Zhi
Highly dense LaCrO 3 negative temperature coefficient (NTC) thermistor ceramics by low-heating solid-state method have been successfully synthesized in air ambient. The X-ray diffraction analysis has shown that both of the calcined powders and as-sintered ceramics crystallize in a perovskite structure. The relative densities of the ceramics synthesized by Cr(NO 3 ) 3 ·9H 2 O and the ceramics synthesized by CrCl 3 ·6H 2 O are 91% and 65%, respectively. The relationship between lnρ and 1000/T shows an approximate line in the measured temperature range. The values of ρ 25 and B 0/25 of the ceramics synthesized by Cr(NO 3 ) 3 ·9H 2 O and the ceramics synthesized by CrCl 3 ·6H 2 O are 424.8 Ω cm, 3252 K and 1835.9 Ω cm, 3636 K, respectively.
High density negative temperature coefficient (NTC) thermistor ceramics Bi 0.2-x Ce x Sr 0.5 La 0.3 TiO 3 (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 × 10 9 –8.99 × 10 7 Ω cm, 2.21 × 10 5 –1.05 × 10 5 Ω cm, and 1.18 × 10 3 –1.13 × 10 3 Ω cm, respectively; the thermal constant B 300/700 is 13385.9–9408.8 K; the activity energy Ea 300/700 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 Bi 0.2-x Ce x Sr 0.5 La 0.3 TiO 3 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.
A series of novel high temperature negative temperature coefficient (NTC) composite ceramics based on (1- x )CaMn 0.05 Zr 0.95 O 3 - x NiMn 2 O 4 ( x = 0, 0.1, 0.2, 0.3) were fabricated by using the solid-state method. The Rietveld refinement method and backscattered electron (BSE) image confirmed the absence of any other phase. The conduction mechanism of the composite ceramics was determined by analyzing the complex impedance and resistance-temperature characteristics, which could be related to the formation of a continuous Mn 3+ -O-Mn 4+ network. The effect of spinel content on the high temperature stability was analyzed using aging tests. The ρ 400°C , ρ 700°C and B 400/700 values of the NTC thermistors were determined to be 4.9 × 10 6 –1.2 × 10 4 , 1.4 × 10 5 –0.8 × 10 3 Ω cm and 12739-5712 K, respectively. This indicated that the electrical properties could be tuned by adjusting the weight ratio of CaMn 0.05 Zr 0.95 O 3 and NiMn 2 O 4 . The findings obtained in this study reveal that the composite NTC thermistor exhibits a good application potential at high temperatures and under harsh environments.
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