上海科技大学知识管理系统

Substitution of La by Sr in the 25% Ni doped charge transfer insulator LaFeO3 leads to structural changes that inflect the electrical conductivity, which is caused by small polaron hopping via charge transfer and exchange interactions. The substitution forms electron holes and causes a structural transition from orthorhombic to rhombohedral symmetry, and then to cubic symmetry. The structural crossover is accompanied by a crossover from the Fe3+-O2--Fe3+ superexchange interaction to the Fe3+-O2--Fe4+ double exchange interaction in the course of substitution, as evidenced by a considerable increase in the conductivity at ambient temperature. The charge transfer and exchange interactions depend on the superexchange angle, which approaches 180 degrees upon increasing Sr concentration. An increase in superexchange angle leads to an increase in overlapping between the O 2p and the Fe/Ni 3d orbitals. (C) 2010 American Institute of Physics. ()[doi:10.1063/1.3517822]