Entanglement of charge transfer, hole doping, exchange interaction and octahedron tilting angle and their influence on the conductivity of La1-xSrxFe0.75Ni0.25O3-{\delta}: A combination of x-ray spectroscopy and diffraction

TL;DR

This study investigates how Sr substitution in LaFeO3 affects its structure, charge transfer, and magnetic interactions, leading to increased electrical conductivity through changes in superexchange interactions and orbital overlaps.

Contribution

It combines x-ray spectroscopy and diffraction to elucidate the relationship between structural crossover, charge transfer mechanisms, and conductivity in doped LaFeO3.

Findings

Structural crossover from orthorhombic to cubic symmetry with Sr doping.

Transition from superexchange to double exchange interactions.

Enhanced conductivity due to increased orbital overlap.

Abstract

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.