Microstructure and electrical properties of xAl2O3-(1-x) LaCrO3 composite NTC ceramics prepared by microwave sintering

xAl2O3-(1-x)LaCrO3 (x = 0.3, 0.4, 0.5, 0.7) composite negative temperature coefficient (NTC) ceramics were prepared by microwave sintering. The effects of different atmospheres and sintering temperatures on microstructure and electrical properties of the NTC ceramics were studied. X-ray diffraction results showed the ceramics were composed of a perovskite structure LaCrO3 and lanthanum hexaaluminate solid solution as well as a separate corundum phase. The existence of Cr3+ and Cr4+, which resulted in skip conduction, was confirmed by X-ray photoelectron spectroscopy. The resistance of the ceramics sintered in air was lower than that of ceramics sintered in an N2 atmosphere. Ceramics sintered in air and N2 showed NTC characteristics starting at 40 °C and 250 °C, respectively. The ρ50 and B300/700 values of the ceramics sintered in air were in the range of 5.06 × 105–2.21 × 109 Ω·cm and 4144–6828 K, respectively. The ceramics prepared at 1400 °C with a holding time of 5 min possessed excellent microstructure and electrical properties. Compared with conventional pressureless sintering, the sintering temperature and holding time of the microwave sintering process were decreased by 6.6–12.5% and 95.8–99.0%, respectively.