Polaron hopping conduction in La$_{0.85}$Sr$_{0.15}$MnO$_3$ single crystal

Temperature dependences of electrical resistance and thermopower of a La$_{0.85}$Sr$_{0.15}$MnO$_3$ single crystal were measured in the paramagnetic and ferromagnetic dielectric phases. It was shown that charge transfer in both phases is due to the variable-range polaron hopping over the localized states. The activation energies in both phases linearly depend on $T^{3/4}$ but differ from each other by a constant which is approximately equal to the exchange energy $kT_c$. The results obtained are in compliance with the concept of percolation character of metal-insulator transition in manganites.