Synthesis and NTC properties of YCr1-xMnxO3 ceramics sintered under nitrogen atmosphere

YCr1-xMnxO3 (0 <= x <= 0.8) negative temperature coefficient (NTC) compositions were synthesized by classical solid state reaction at 1200 degrees C, and sintered under nitrogen atmosphere at 1500 degrees C and 1600 degrees C. XRD patterns analysis has revealed that for x <= 0.6, the structure consists of a solid solution of an orthorhombic perovskite YCrO3 phase with Mn substitute for Cr. For x >= 0.8, a second phase with a structure similar to the hexagonal YMnO3 phase appears. SEM images and calculated open porosity have shown that the substitution of Mn for Cr results in a decrease in porosity. Whatever the sintering temperature, the electrical characterizations (between 25 and 900 degrees C) have shown that the increase in the manganese content involves the decrease in both resistivity and material constant B (parameter which characterizes the thermal sensitivity of material) when x <= 0.6. The magnitude order of the resistivity at 25 degrees C is of 10(4)-10(8) Omega cm and activation energies vary from 0.28 to 0.99 eV at low and high temperatures, respectively. (C) 2011 Elsevier Ltd. All rights reserved.