Enhanced room temperature coefficient of resistivity (RT-TCR) and broad metal-insulator transition temperature (TMI) of La0.67Ca0.33-xAgxMnO3 polycrystalline ceramics

Polycrystalline La0.67Ca0.33-xAgxMnO3 (LCAMO, x = 0, 0.06, 0.15, 0.18, and 0.24) ceramics were fabricated by conventional sol-gel route at relatively low sintering temperature of 1100 degrees C for 12 h. Effects of silver content (x) on crystal structure, grain size, resistivity and magnetic properties of as-prepared LCAMO specimens were investigated by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), elemental mapping and energy dispersive spectrometry (EDS), X-ray photoelectron spectroscopy (XPS), and standard four-probe method (rho-T). The data from XPS, XRD and EDS revealed that silver existed as Ag ions in the lattice matrix position of LCAMO ceramics. Broad metal-insulator transition temperature (T-MI) values ranging from 267.0 K (x = 0) to 302.6 K (x = 0.24) were obtained with LCAMO specimens prepared with variable Ag+ added contents. Peak temperature coefficient of resistivity (TCR) enhanced from 4.1% K-1 at 263.2 K (for x = 0) to 10.9% K-1 at 278.5 K (for x = 0.18), and reached 7.5% K-1 at room-temperature (295.9 K) for x = 0.24. Meanwhile, magnetoresistance (MR) of materials reached 17.7% at room-temperature (299.2 K) for x = 0.24. Overall, these findings demonstrated that Ag doping was beneficial for improving electrical and magnetic properties of LCAMO materials. In summary, LCAMO ceramics achieved RT-TCR and MR at optimal Ag stoichiometric ratio, promising for applications in infrared bolometers or magnetic sensors.