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

YCr_1−xMn_xO₃ (0 ≤ x ≤ 0.8) negative temperature coefficient (NTC) compositions were synthesized by classical solid state reaction at 1200 °C, and sintered under nitrogen atmosphere at 1500 °C and 1600 °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 °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 °C is of 10⁴-10⁸ Ω cm and activation energies vary from 0.28 to 0.99 eV at low and high temperatures, respectively.