Novel electrical properties of Mn-doped LaCrO3 ceramics as NTC thermistors

Abstract

A series of Mn-doped LaCrO3 ceramics, LaCr1−xMnxO3 (x = 0.0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, the concentration of doping Mn), were synthesized by traditional solid-state reaction and their novel electrical properties as the negative temperature coefficient (NTC) thermistors were first investigated. X-ray diffraction results indicate that the Mn-doped LaCrO3 ceramics formed a solid solution with an orthorhombic perovskite structure when x ≤ 0.6, with a tiny amount of Mn2O3 remaining when x = 0.7. The SEM/EDS images and calculated relative densities show that all the LaCr1−xMnxO3 ceramics had a uniform grain size distribution, accurate stoichiometric ratio and high density over 98.0%, enabling them to have high stability. After aging for 1000 h at 150 °C in air, the resistance shifts ΔR/R0 were less than 0.57%. The investigation of electrical properties manifests that the LaCr1−xMnxO3 ceramics had excellent NTC characteristics, and that their resistivities and thermal constants decreased with increasing Mn content and exhibited high controllability. The ρ25°C, B25/50 and activation energy Ea varied in the range of 15.0–51,505.3 Ω cm, 3191–4301 K, and 0.28–0.37 eV, respectively. This combination of parameters makes this system an outstanding candidate for NTC thermistors applied to a low temperature range from − 100 to 200 °C.