Tolerance factor mismatch-induced phase coexistence in LaFe1−xNixO3: Mössbauer spectroscopy insights

LaFe[Formula: see text]Ni x O 3 ([Formula: see text]) samples were synthesized via the sol–gel method, and the phase coexistence behavior was systematically investigated using X-ray diffraction (XRD) and Mössbauer spectroscopy. XRD analysis revealed a continuous structural transition from the orthorhombic Pnma to the rhombohedral R3c phase with increasing Ni content. A distinct two-phase coexistence was observed in the doping range of [Formula: see text]. Mössbauer spectroscopy enabled quantitative determination of the Fe ion distribution across the coexisting phases. The R3c phase first emerged at [Formula: see text], contributing 30.5%, and became predominant at [Formula: see text] with a contribution of 81.5%. At [Formula: see text], the R3c phase became exclusively present. Importantly, this work is the first to report distinct differences in the electronic environments of Fe ions between the Pnma and R3c phases in the LaFe[Formula: see text]Ni x O 3 system. Such variations are attributed to mismatches in the tolerance factor, which influence both the global crystal symmetry and the local coordination of Fe ions. These findings offer compelling experimental evidence for understanding the microscopic mechanisms governing phase coexistence, thereby contributing to the theoretical basis for designing advanced functional materials.