Electrical properties of Ag-La0.67Sr0.33MnO3

A series of La0.67Sr0.33MnO3/Ag composites were synthesized using a sol-gel method followed by a conventional solid-state reaction route. The temperature dependence of the magnetic properties and electrical resistivity has been investigated between 80 and 450 K. Except for the sample with x = 0.01, Ag addition has increased the conductivity of this system dramatically. Curie temperature (T-C) is almost independent of Ag content and is 352 K for Ag-dopant samples, while the metal-insulator transition temperature T-p increases with Ag addition, which is mainly due to the improvement of grain boundaries and opening a new metal conductivity channel caused by the segregation of Ag on the grain surfaces. At low temperature, the rho - T curves are fitted well by the expression of rho = rho(0) + rho T-2(2) + rho T-4.5(4.5) while all data for the above T-C can be fitted by using the adiabatic small-polaron-hopping model rho = rho T-0 exp(E/k(B)T).