  Substitution of La by Sr in the 25% Ni doped charge transfer insulator LaFeO3
creates structural changes that inflect the electrical conductivity caused by
small polaron hopping via exchange interactions and charge transfer. The
substitution forms electron holes and a structural crossover from orthorhombic
to rhombohedral symmetry, and then to cubic symmetry. The structural crossover
is accompanied by a crossover from Fe3+-O2--Fe3+ superexchange interaction to
Fe3+-O2--Fe4+ double exchange interaction, as evidenced by a considerable
increase of conductivity. These interactions and charge transfer mechanism
depend on superexchange angle, which approaches 180{\deg} upon increasing Sr
concentration, leading an increased overlap between the O (2p) and Fe/Ni (3d)
orbitals.
