The temperature dependences of the resistivity r and the heat conductivity k of La Ca Mn Fe O (0,x,0.12) fixed valence 0.7 0.3 12x x 32d
doped crystals were studied between 50 and 340 K using the time resolved thermoelectric effects (TTE-method). The heat conductivity k
is dominated by the lattice contribution and changes from a crystalline to a randomized scenario with increasing Fe-content. We also
observe a splitting of the Curie and metal–insulator transition temperature T .T which we assign mainly to a small oxygen deficit in c mi
the TTE-measured sample surface layer. Steps in k at T , Dk , are assigned to polaronic effects. Dk changes sign with increasing x, mi mi mi
suggesting that Fe–Fe pairs in octahedral settings take over from the single Fe-sites (dilute limit) already at x50.04. For x.0.06,
structures in k(T ) suggest that larger Fe-based clusters are introduced.