Sintering and electrical properties of Cu-substituted Zn-Co-Ni-Mn spinel ceramics for NTC thermistors thick films

We report on the preparation, sintering and electrical properties of new Cu-substituted spinels Zn0.5Ni0.4Co0.4Mn1.7-xCuxO4 and Zn0,5Ni0,5Co0,5Mn1,5-xCuxO4 (0.1 ≤ x ≤ 0.4) for thick film NTC thermistors. Bulk samples were sintered at 900 °C and Cu-rich spinels achieve high density. The thermal stability is limited by the decomposition temperature Td. However, a Td ≥ 900 °C for x = 0.4 allows firing of bulk samples and films at 900 °C. The room temperature resistivity and thermistor B-values decrease with x. NTC thermistor thick films were fabricated by screen-printing of spinel pastes (x = 0.4) onto alumina substrates and firing at 900 °C. Addition of BBSZ glass to the thermistor paste allows for sintering of the films at 850 °C. The NTC thermistor films exhibit excellent thermistor performance with R□25°C = (652 ± 5) kΩ/sq, B = (3342 ± 17) K, and good ageing stability (< 2% after 600 h at 150 °C).