Large temperature coefficient of resistivity (TCR) of La_0.67Ca_0.33MnO₃ polycrystalline ceramics improved by optimizing sintering temperatures

This work investigates fabrication of La0.67Ca0.33MnO3 (LCMO) polycrystalline ceramics using a facile sol-gel method at sintering temperatures (T-s) ranging from 1470 degrees C to 1540 degrees C and explores relationship between their electrical transport properties and T-s. X-ray diffraction, scanning electron microscopy, energy-dispersive spectroscopy, and X-ray photoemission spectroscopy were employed to characterize crystal structure, morphologies, element distributions, and Mn3+/Mn4+ ratio of the as-obtained LCMO ceramics. The influence of T-s on phase purity, microstructure, morphology, and electrical transport properties was also investigated. LCMO ceramics exhibit increased grain size and higher temperature coefficient of resistivity (TCR) at higher temperatures. An increase in T-s can reduce the strength of electron-lattice interactions and theoretical Curie temperature in LCMO ceramic samples, which can in turn optimize their electrical transport properties. Moreover, an increase in T-s enhances double-exchange (DE) effect to some extent. The DE effect further affects resistivity and metal-insulator transition temperature of material. Additionally, small-polaron hopping model and phenomenological percolation model were used to characterize electrical transport in metal-insulator transition region. The temperature at which TCR is maximum (265.78 K) and the largest TCR value (58.16 %) were achieved at a T-s of 1530 degrees C. By modulating the sintering temperature, we achieved LCMO ceramics with larger grains and enhanced electrical properties. This optimization renders materials suitable for highly sensitive infrared bolometer applications.