Effect of sintering temperature on structure and electrical transport properties of La0.7Ca0.26Na0.04MnO3 ceramics

LCNMO (La0.7Ca0.26Na0.04MnO3) ceramics are prepared via the sol-gel method and sintered at different temperatures, ranging from 1000 to 1300 °C. The influences of sintering temperature on structure and electrical properties are systematically investigated. X-ray diffraction analysis reveals that uniform phase of perovskite structure is formed after sintering. Furthermore, scanning electron microscope (SEM) images demonstrate the presence of on the surface, a highly dense grain boundary and an average grain size of ~2.5 μm. The resistivity-temperature (ρ-T) measurement shows that the resistivity decreases with increased sinter temperature. Moreover, the metal-insulation transition temperature (Tp) and peak resistivity (ρmax) gradually decreased with increasing sintering temperature. The influence of various scattering mechanisms on resistivity at low temperatures is studied, revealing that the residual resistivity (ρ0) dictates the electrical transport performance of the LCNMO ceramics. Also, the different models employed to analyze the ρ-T curves in the temperature range of 100–300 K, confirming the occurrence of phase-separation mechanism in the entire temperature range. The resistance temperature coefficient (TCR) of 10.6%·K−1 and maximum magnetic resistance (MRmax) of 57.12% are achieved after sintering at 1200 °C. These results indicate that LCNMO are promising candidates for infrared detector and magnetic sensor.