Enhanced room-temperature MR and TCR in polycrystalline La-0.67(Ca0.33-xSrx)MnO3 ceramics by oxygen assisted sintering

摘要

Polycrystalline La-0.67(Ca0.33-xSrx)MnO3 (LCSMO, x = 0, 0.03, 0.06, 0.09, 0.12, and 0.15) ceramics were prepared by sol-gel method. Microstructures, electrical/magnetic transport properties, temperature coefficient of resistance (TCR) and magnetoresistance (MR) behaviors, were all investigated. X-ray diffraction (XRD) results showed that all samples crystallized in single phases without detectable secondary phases. At Sr doping (x) above 0.12, crystal structures transformed from orthorhombic phase (space group of Pnma) to rhombohedral phase (space group of R (3) over barc). As x content further rose, metal-insulator transition temperature (T-p) increased and maximum values of TCR and MR decreased. Further data revealed that TCR and MR peaks were controlled by Sr doping level x. In addition, room temperature MR and TCR of LCSMO ceramics were enhanced under oxygen assisted sintering. At Sr doping x = 0.09, the value of T-p attained room temperature (301.8 K), and the maximum values of TCR and MR reached 10.5% K-1 and 43.0%, respectively. These properties were related to combination of double exchange (DE) and Jahn - Teller effects. LCSMO materials may have promising future use in photoelectric (uncooled bolometer or infrared detectors) or magnetic devices (uncooled magnetic sensors) at room temperature.