Effect of Al2O3 addition on the microstructure and electrical properties of LaMnO3-based NTC thermistors

Abstract

A study to develop a new system of negative temperature coefficient thermistors for wide temperature range, A series of Mn-based perovskite-structured ceramics of composition (LaMn1−x Al x O3)0.9(Al2O3)0.1 has been synthesized by conventional solid state reaction at 1350 °C. The X-ray diffraction patterns showed that for all the samples, the substitution of manganese by aluminum up to x = 0.1 preserved the rhombohedral perovskite LaMnO3-like phase. For x = 0.2, apart from the LaMnO3-like structure, a second perovskite phase based on the cubic LaAlO3 structure was formed. For x = 0.3 and 0.4, the phase present was LaAlO3 -type structure. The grain sizes of the sintered body detected by scanning electron microscope were decreased with increasing Al2O3 content. The resistivity increases with increasing the Al content. The obtained values of ρ 25 °C and B 25/50 and E a are in the range of 10–13103 Ω cm, 1813–2794 K, 0.156–0.241 eV, respectively. The resistance variation (ΔR/R) was <0.241% and the minimum value (0.0483%) was obtained for aging at 125 °C at 500 h. The aim of this work was explored new composite ceramics materials, which could be used as potential candidates for wide temperature range from −100 to 500 °C thermistors applications.