Preparation and characterization of negative temperature coefficient (Ni,Mn)3O4–La(Mn,Ni)O3 composite

Abstract

The composites made of spinel-structured (Ni, Mn) 3 O 4 and perovskite-structured La(Mn,Ni)O 3 were investigated for potential application as negative temperature coefficient (NTC) thermistor. The composites were prepared using the standard ceramic route. The electrical resistivity of the composite at 25°C was found to decrease by one to two orders of magnitude depending the amount of the low-resistivity perovskite phase, while the thermal constant determining the temperature sensitivity of the NTC thermistor was still reasonably large in the range of 4,000 to 3,000 K, and the resistivity drift after annealing at 150°C for 1,000 h in air was relatively small (∼1.2%). The general effective media model was adopted to fit the electrical resistivity data of the composites, giving a value of 0.37 for the percolation volume fraction of the perovskite phase. This work demonstrates that it is possible to tune the electrical resistivity and thermal constant of the spinel-structured oxide through making composite with low-resistivity perovskitestructured oxide.

Negative Temperature Coefficient Resistance (NTCR) Ceramic Thermistors: An Industrial Perspective

“…Later, in 2000, Feltz 62 reported on the preparation, structure, and electrical properties of Sr x La 1Àx Ti x1y Co y III Co 1ÀxÀ2y II O 3 (0oxo1, 0oyo(1Àx)/2) ceramics. Zhao et al 76 also investigated the NTCR behavior of ceramic composites, but based on a mixture between the Ni 0. In 2002, Gutierrez et al 72 74 Based on their data, it appears that the two first materials show NTCR characteristics that are useful for applications only from room temperature to 3001C, whereas the third are useful from 3001 to 8001C.…”

“…Interestingly, the Ba 1Àx K x-BiO 3 and BaPb 1Ày Bi y O 3 were reported to show superconductivity at 30 K (x 5 0.4) and 12 K (y 5 0.3), respectively. Zhao et al76 also investigated the NTCR behavior of ceramic composites, but based on a mixture between the Ni 0.75 Mn 2.25 O 4 spinel phase and the LaMnO 3 perovskite phase. Although they have elegantly fitted experimental resistivity values with an effective media model, transfer of this approach to the industry might not be so straightforward, because of reproducibility difficulties.…”

Negative Temperature Coefficient Material with Low Thermal Constant and High Resistivity for Low‐Temperature Thermistor Applications

“…The composites consisted of cubic‐structured spinel phase and cubic‐structured YSZ, and no other phase was observed. The sintered composite samples were found to possess a density of 93.0%–94.8% relative to the theoretical density ( D th ) which is in turn determined according to the summation law 18 : where M Spinel and M YSZ are molar weight of Fe 0.5 Cu 0.2 Ni 0.66 Mn 1.64 and Zr 0.84 Y 0.16 O 1.92 , x the molar fraction of the spinel phase, V Spinel and V YSZ are the molar volume of the respective phases.…”

“…The composites consisted of cubic-structured spinel phase and cubic-structured YSZ, and no other phase was observed. The sintered composite samples were found to possess a density of 93.0%-94.8% relative to the theoretical density (D th ) which is in turn determined according to the summation law 18 : Figure 3 shows the SEM images obtained from the surface of the as-sintered samples. It can be seen that there are two types of grains with different gray level.…”

“…One way to fill these blank regions is to introduce a second phase of different resistivity into the spinel oxide matrix. For example, a material with low ρ and high B has been obtained by introducing LaMnO 3 second phase into Ni–Mn–O spinel 18 ; the former is of low ρ and latter of high ρ and high B . In principle, the material with high ρ and low B may also be obtained through introducing a second phase of high ρ into a spinel oxide of low ρ and low B .…”