The aim of the present work was the characterization of a group of compounds with the perovskite‐type structure in respect of their applicability as thermistor materials.
Four compositions: La0.7Sr0.3Zr0.5Co0.22+Co0.33+O3, La0.8Sr0.2Ti0.5Co0.32+Co0.23+O3, La0.4Sr0.6Ti0.3Fe0.7O3 and CaTi0.8Co0.2O3 were synthesized by solid‐state reaction. Ceramic thermistor materials were sintered in the temperature range 1,300‐1,400°C. The synthesized powders were used for fabrication of thick film pastes and thermistors fired at 1,100‐1,250°C. Resistance‐temperature characteristics of the ceramic samples were studied in the range −55 to 800°C for the ceramic samples and 20‐600°C for thick films. Endurance tests at 300°C for 500 h were performed.
The developed NTC materials exhibited high temperature coefficients of resistivity, dense microstructure and good stability. The most advantageous characteristics have been shown by La0.7Sr0.3Zr0.5Co0.22+Co0.33+O3 and La0.8Sr0.2Ti0.5Co0.32+Co0.23+O3 thermistors. The highest Temperature coefficient of resistances for the ceramics were found in the temperature range from −55 to 180°C (−10.7 to −2.9 per cent/°C) and for the thick films in the temperature range 40‐300°C (−5.6 to −1.5 per cent/°C).
This work has been focused on preliminary choice of compositions appropriate for practical thermistor thick film applications. Elucidation of conduction mechanism of the investigated materials needs further complex studies of conductivity, nonstoichiometry, thermoelectric power, etc. as a function of temperature and oxygen partial pressure.
In this work, an attempt has been made to extend the typical range of NTC compositions and to fulfil the demand for improved stability of bulk and thick film thermistors at elevated temperatures.
J. Kulawik, D. Szwagierczak, B. Gröger and A. Skwarek (2007) "Fabrication and characterization of bulk and thick film perovskite NTC thermistors", Microelectronics International, Vol. 24 No. 2, pp. 14-18Download as .RIS
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