Effects of substituting Ca2+ on the structure and electrical properties of 0.6Y2O3–0.4YCr0.5Mn0.5O3 composite NTC ceramics

Abstract

New high temperature negative temperature coefficient (NTC) thermistors based on the 0.6Y2O3–0.4Y1−x Ca x Cr0.5Mn0.5O3 (0 ≤ x ≤ 0.15) composite system have been prepared through the conventional solid-state reaction. The effects of Ca doping on the structure and electrical properties of 0.6Y2O3–0.4Y1−x Ca x Cr0.5Mn0.5O3 have been investigated. The major phases presented in the samples are Y2O3 phase and orthorhombic perovskite phase isomorphic to YCrO3. The resistance decreases with increasing temperature from 25 to 1000 °C, indicative of NTC characteristics. The resistance of NTC thermistors decreases with the increase of Ca content as a result of the enhancement of Cr4+ and Mn4+ concentration, which has been explained by using defect chemistry theory. The values of ρ 25, B 25−150 and B 700–1000 of 0.6Y2O3–0.4Y1−x Ca x Cr0.5Mn0.5O3 NTC thermistors are in the range of 2.73 × 104–3.86 × 105 Ω cm, 2952–3553, 5790–8391 K, respectively. These values can be tuned with the Ca content. These compounds could be used as potential candidates for high temperature thermistors applications.