Electrical properties of Ni0.5Co0.8Mn1.7O4 and Ni0.5Co1.1Mn1.4O4 negative temperature coefficient ceramics doped with B2O3

Abstract

The influence of B2O3 addition as a sintering aid on the electrical and microstructure properties of Ni–Mn-Co–O based negative temperature coefficient (NTC) ceramics were reported. For this purpose, our focus was to produce NTC thermistors with B2O3 additive without calcination. The B2O3-added Ni0.5Co0.8Mn1.7O4 and Ni0.5Co1.1Mn1.4O4 NTC thermistors were fabricated by the traditional ceramic processing techniques and were sintered at 900, 1000, and 1100 °C without calcination. X-ray diffraction analysis of the sintered samples was performed to determine the formation of crystalline phases. According to XRD results, cubic spinel phase was obtained as a main phase in all samples. The existence of Mn3O4 phase was determined in the samples sintered at 900 °C and disappeared when sintering temperature increased to 1100 °C. The electrical resistivity of the NTC ceramics reduced substantially with an increase in sintering temperature. A similar effect on the electrical resistivity was observed with the increase in the amount of cobalt oxide. The electrical resistivity of samples was found between 550 and 3844 Ω.cm. The electrical properties result also showed that material constant (B25/85) values are in the range of 3421–3656 K. It is important to produce NTC thermistor with low electrical conductivity and high B value. The highest B value with lower electrical resistivity is obtained for the 0.1 mol B2O3-added Ni0.5Co1.1Mn1.4O4 sample sintered at 1100 °C. These results showed that the B2O3 addition is effective in achieving similar electrical properties without calcination compared to B2O3-free NTC thermistors. Alternatively, NTC thermistors with B2O3 addition can be sintered at a lower temperature, continuing to achieve industry-suitable specifications.