Complex impedance analysis of (Y2O3 +CeO2)–YCr0.5Mn0.5O3 composite NTC ceramics

Abstract: Ceramic compositions based on (aY2O3 + bCeO2)–0.4YCr0.5Mn0.5O3 (a + b =0.6) were prepared by conventional solid state reaction at 1200°C, and sintered under air atmosphere at 1600°C. For 0≤ a <0.6, XRD patterns have shown that the major phases presented in the calcined powders are Y2O3, CeO2 and orthorhombic perovskite YCr0.5Mn0.5O3 phase, respectively. SEM and EDAX observations confirm the YCr0.5Mn0.5O3 phases mostly exist at the grain, whereas the Y2O3 and CeO2 phases mainly exist at the grain boundaries. Complex impedance analysis shows that, for 0< a ≤0.6, single semicircular arc whose shape does not show any change with temperature. Nevertheless, for a =0, two overlapping semicircular arcs are observed at and above 300°C. The grain boundary properties exhibit thermistor parameters with a negative temperature coefficient characteristic. The relaxation behavior and conduction for the grain boundary could be due to a space-charge relaxation mechanism and oxygen vacancies, respectively. [Copyright &y& Elsevier]