YCr0.5Mn0.5O3 negative temperature coefficient perovskite ceramics sintered under reducing atmosphere: Microstructure and electrical properties

Instead of the common oxidizing atmosphere, three-phase high-temperature negative temperature coefficient (NTC) materials were prepared under reducing atmosphere from raw powders by conventional solid-state method in the Y2O3-Mn2O3-Cr2O3 ternary diagram. Owing to dilatometric analysis, the sintering stage was performed at 1500 °C for 1 h, 12 h, and 30 h under reducing atmosphere (1 % H2 – 99 % N2) whereas sintering is not reached at 1600 °C in air atmosphere. The sintered ceramics had 96 to 98 % of relative density. XRD patterns and SEM observations revealed that the sintered pellets consist of three phases: a phase with a structure similar to that of the orthorhombic perovskite YCrO3 and two other phases with structures close to that of Y2O3 and a solid solution of MnO. The results of electrical measurements as a function of temperature have shown that despite this dissociation of the phases, samples kept an NTC behavior with interesting characteristics for low and high temperatures: the resistivity increased slightly with dwell time, but the order of magnitude remained unchanged (105 Ω*cm) at 25 °C… Depending of the dwell time, activation energy obtained from material constant B varied from 0.276 eV at low temperature to 0.690 eV at high temperature. Such materials could be successfully used as potential candidates for temperature sensors applications in a wide range temperature from ambient temperature to 1000 °C.