Effect of sintering temperature on room-temperature electrical and magnetic properties of La0.625(Ca0.315Sr0.06)MnO3 polycrystalline ceramics

Abstract

Polycrystalline La0.625(Ca0.315Sr0.06)MnO3 (LCSMO) ceramics were prepared by conventional sol-gel method at different sintering temperatures (Ts) of 1273, 1373, 1473, 1573, and 1673 K. Structures, electrical and magnetic properties of obtained LCSMO ceramics were investigated by various analytical techniques. X−ray diffraction (XRD) identified structures of all ceramics as pure perovskite LCSMO phase with Pnma space group. Scanning electron microscopy (SEM) revealed improvements in surface compactness and homogeneity of LCSMO ceramics prepared at various Ts. As Ts rose, resistivity (ρ) dropped and both peak temperature coefficient of resistance (TCR) and magnetoresistance (MR) increased. This, in turn, improved crystalline quality and microstructure of LCSMO ceramics. For LCSMO ceramics sintered at 1673 K, the TCR and MR peaks reached maxima of 4.15% (294.5 K) and 17.4% (296.7 K), respectively. X−ray photoelectron spectroscopy (XPS) suggested no change in La, Ca and Sr, indicative of stable proportion of Mn3+ and Mn4+. The increase in Ts caused lattice distortion and suppressed double exchange (DE) interaction. The latter changed the metal to insulator transition temperature (Tp) of the materials. Overall, room−temperature (295–300 K) electrical and magnetic properties of LCSMO ceramics could significantly be enhanced by increasing Ts.