Effect of sintering temperature on structural and electrical transport properties of La0.7Ca0.28K0.02MnO3 ceramics

Manganites with large temperature coefficient of resistance (TCR) have been considered as potential candidate for infrared detecting. To date, A-site doping with alkaline-earth metal (+2 oxidation state) has been widely used to improve the TCR. However, doping with alkali ions (+1 oxidation state) was less explored. In this study, 2% K doped La0.7Ca0.28K0.02MnO3 (LCKMO) ceramics were prepared by sol-gel method and sintered within the temperature range of 1000–1300 °C for structural and electrical transport properties investigation. X-ray diffraction (XRD) analysis demonstrated that all samples exhibited an orthorhombic perovskite structure with space group Pnma. Elevated sintering temperature would lead to an increase in grain size, which could account for the concurrent decrease of the resistivity (ρ). By optimizing the sintering process, the magnetoresistance (MR) and TCR reached their maxima of 60.95% and 13.54% K−1, respectively, for sintering temperature of 1200 °C. By fitting the temperature dependence of resistivity (ρ-T), grain boundary scattering and small-polaron hopping (SPH) were found to dominate in the low-temperature ferromagnetic and high-temperature paramagnetic regions, respectively. In addition, the ρ-T in the whole temperature range of 100–300 K can also be explained by the percolation model.