A novel LaAl1-xNbxO3 NTC ceramic with excellent stability for high-temperature thermistor

Abstract

A series of LaAl1-xNbxO3 (0 ≤ x ≤ 0.100) samples were synthesized via the solid phase method. Characterization techniques including X-ray diffraction (XRD), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS) confirmed the formation of a solid solution in LaAl1-xNbxO3 (0 ≤ x ≤ 0.100) materials without the emergence of additional phases following Nb doping. Transmission electron microscopy (TEM) revealed distinct lattice fringes with a d value of 0.274 nm, corresponding to the (110) plane of LaAlO3 (PDF #82–0478). The introduction of Nb dopant caused distortions in the cell parameters of LaAlO3 due to ionic radius size effects, changes in Nb valence, fluctuations in oxygen vacancy concentration and Coulomb forces. Specifically, the lattice exhibited a shrinkage for 0 ≤ x ≤ 0.025, expansion for 0.025 <x ≤ 0.075, and subsequent shrinkage for 0.075 <x ≤ 0.100. Resistance measurements indicated that LaAl1-xNbxO3 (0 ≤ x ≤ 0.100) materials exhibited favorable negative temperature coefficient (NTC) characteristics in the temperature range of 600 °C–1400 °C. Hall measurements revealed that the materials functioned as P-type semiconductors with hole carriers, and Nb doping enhanced carrier concentration. Aging tests demonstrated that the aging drift rate of LaAl0.9Nb0.1O3 could be as low as 0.906% after aging it at 1000 °C for 500 h, a crucial parameter for practical applications of LaAl1-xNbxO3 (0 ≤ x ≤ 0.100) materials in high-temperature NTC applications.