Structural and electrical properties of FeMg0.7Cr0.6Co0.7−xAlxO4 (0 ≤ x ≤ 0.3) thick film NTC thermistors

The microstructure and electrical properties of FeMg0.7Cr0.6Co0.7−xAlxO4 (x = 0, 0.1, 0.2, and 0.3) thick film negative temperature coefficient (NTC) thermistors, fabricated by screen printing, were studied. The sintered FeMg0.7Cr0.6Co0.7−xAlxO4 bodies were the solid solutions of the constituent oxides along with a small amount of MgAl2O4. The electrical resistivity increased with sintering temperature mainly because of an increase in the amount of insulating MgAl2O4 resulting from the partial decomposition of the solid solutions during sintering. In addition, the added Al2O3 led to a significant increase in the resistivity. The effect of the sintering temperature and Al2O3 on the electrical properties of the NTC thermistors was discussed.