Coexistence of pd σ hybridization conduction and double-exchange conduction in heavily doped La 1.85 − 2 x Sr 0 . 1 5 + 2 x Cu 1 − x Mn x O 4

Double-doped samples La 1 . 8 5 - 2 x Sr 0 . 1 5 + 2 x Cu 1 - x Mn x O 4 (0.1≤x≤0.5) have been prepared. The possibility of Mn-O chain formation and its conduction mechanism in this system are discussed. With the increase of x, the room-temperature resistivity (p) is enhanced three orders, whereas the ρ-T relation presents unlike forms in different ranges of x. In the scope of compositions 0.1≤x≤0.3, the resistivity displays the behavior of thermal activation undergoing Kondo scattering. At the doping level 0.32≤x≤0.5, it is surprising that the resistivity at 20 K drops three orders of magnitude compared to that of x=0.3 and the behavior of the susceptibility versus temperature curves is quite different in the two doping ranges. We suggest that double-exchange Mn-O-Mn chains have come into being besides Cu-O-Cu pdσ channel with doped Mn. In the range of 0.32≤x≤0.35, Mn-O-Mn forms clusters in the parent body. The conduction mechanism of Mn-O-Mn chains formed by clusters is variable-range hopping, while for 0.38≤x≤0.40 the clusters are connected to Mn-O-Mn channels. The conduction mechanism of this channel is small-polaron conduction. The coexistence of two kinds of paths, the pdσ channel and Mn-O-Mn chains, dominates the conduction behavior.