Structural and electrical properties of La0.67(Ca0.3Sr0.03)MnO3 composites prepared with added Ag

Abstract

In this account, La0.67(Ca0.3Sr0.03)MnO3:mol%Agx (LCSMO:Agx, 0 ≤ x ≤ 0.5) high-density composites were successfully prepared by the conventional sol-gel method using deionized water as solvent. The structures, surface morphologies and electrical transport properties of obtained composites were analyzed by various analytical methods. The X-ray diffraction (XRD) profiles of LCSMO:Agx exhibited single perovskite structure with pure orthorhombic crystal structure (Pnma space group) and without presence of traces secondary phases. Field emission scanning electron microscopy (FESEM), XRD and X-ray photoemission spectroscopy (XPS) depicted good grain surface connectivity of the specimens. In addition, grain size increased with Ag doping. The influences of Ag2O doping on materials electrical properties were also explored. The results indicated the presence of silver as Ag+ ions substituting A-site ions. Furthermore, small amounts of metallic silver gathered at the grain boundaries (GBs) were detected. This increased both the MnO bond length and MnOMn bond angle, and slightly expanded both cell volume (V) and lattice constant (a, b, c). The maximum value of temperature coefficient of resistivity (TCR) reached 11.2% K−1 with peak TCR temperature (Tk) of 281.5 K. The improved electrical transport performances of LCSMO:Agx materials were attributed to Ag doping, which enhanced Mn4+ ion amounts and GBs connectivity in each specimen. In addition, excess replacement of A-site ions by Ag+ expanded the metal-insulator transition characteristics and reduced the temperature coefficient of resistivity. Finally, a double exchange based mechanism was proposed to explain the above results.