57Fe Mossbauer Spectroscopy at 6 K on La-Sr-Fe-Ni-O perovskite materials

57Fe Mossbauer Spectroscopy was conducted on six perovskite powders, synthesised by an optimised auto-combustion route followed by calcination at 1080 °C for 2 h and ball-milling. The compositions are La₀.₈Sr₀.₂Fe₀.₉Ni₀.₁O₃₋δ (LSFN8291), La₀.₇Sr₀.₃Fe₀.₉Ni₀.₁O₃₋δ (LSFN7391), La₀.₆Sr₀.₄Fe₀.₉Ni₀.₁O₃₋δ (LSFN6491), La₀.₇₂Sr₀.₁₈Fe₀.₉Ni₀.₁O₃₋δ (LSFN8291A), La₀.₆₃Sr₀.₂₇Fe₀.₉Ni₀.₁O₃₋δ (LSFN7391A), and La₀.54Sr₀.36Fe₀.₉Ni₀.₁O₃₋δ (LSFN6491A). Mössbauer spectra provide direct, bulk-averaged quantification of the Fe³⁺/Fe⁴⁺/Fe⁵⁺ distribution across the LSFN series. Five spectral sub-components were resolved in each spectrum. Sub-spectra Q1, Q2, and Q3 (isomer shifts = 0.3–0.5 mm s-1) are assigned to high-spin octahedral Fe³⁺ environments characteristic of LaFeO₃-type perovskites. The Q4 component (δ_IS ≈ 0.08–0.13 mm s⁻¹, B_hf > 30 T) is attributed to Fe4+. Most strikingly, a Q5 sub-spectrum with anomalously low isomer shift (δ_IS = −0.13 to −0.04 mm s⁻¹) is detected, which is a signature of Fe5+.

Funded by the European Union (Horizon Europe), KNOWSKITE-X, grant agreement No. 101091534.