La1-xCaxMnO3 NTC ceramics for low temperature thermistors with high stability

Abstract

A new perovskite-structured NTC ceramic with high stability for low temperature thermistors, the La1-xCaxMnO3 (0 ≤ x ≤ 0.25) system, was originally explored by the conventional solid-state reaction. XRD analysis confirmed that the sintered La1-xCaxMnO3 ceramics were composed of a hexagonal perovskite when x ≤ 0.05 and an orthorhombic perovskite when x ≥ 0.1 with a tiny amount of Mn3O4 phase. SEM images showed that the grain size and the segregated Mn3O4 both decreased with Ca content increasing. The effects of Ca doping on the electrical properties were also investigated. With Ca increasing, the resistivity ρ decreased slowly within a narrow range (ρ25 °C: 1.52–4.13 Ω•cm), while the B25/50 value decreased sharply (from 1559 K to 385 K). Such combination of parameters enables it a potential candidate for NTC thermistors applied to low temperature. The thermal stability was also obviously improved by Ca doping, reducing △R/R0 from 10.91% (x = 0) to 0.25% (x = 0.20) after aging at 125 °C for 1000 h.