Preparation of La0.67Ca0.33MnO3:Ag x polycrystalline by sol–gel method

La_0.67Ca_0.33MnO₃:mol%Ag _x (LCMO:Ag _x , x = 0, 0.04, 0.08, 0.10 and 0.20) ceramics were prepared by sol–gel method. The X-ray diffraction studies of the LCMO:Ag _x samples confirm the pure phase of the LCMO composites with Pbnm space group. With the increase of Ag doping from x = 0 to 0.20, the normalized resistivity (ρ/ρ _300K ) of the samples around the metal–insulator transition temperature (T _p ) reduced in sequence. Both T _p and the peak of temperature coefficient of resistance (T _k ) improved 5–8 K. Energy dispersive X-ray spectroscopy analysis showed that the composition of La, Ca and Mn of the obtained LCMO composites was in accordance with the composition of the precursor. The results indicated that the improvement of grain boundaries and crystallization were responsible for the enhancements of ρ, T _p and T _k of LCMO:Ag _x composites. The fitted curves of electrical resistivity for LCMO:Ag _x composites indicated that the mechanisms of grain/domain boundary, electron–electron and magnon scattering and adiabatic small polaron hopping are proposed to explain the phase transition of ferro-magnetic metallic region (T < T _p ) and the para-magnetic insulating region (T > T _p ), respectively.