Phase evolution of KFeO2 synthesized by sol-gel auto-combustion: Effect of precursor composition on iron oxide suppression

Potassium ferrite (KFeO 2 )-containing powders were synthesized by sol–gel auto-combustion using two precursor compositions to assess reagent redesign effects on phase formation, iron oxide suppression, and nanostructural refinement. X-ray diffraction and Rietveld refinement showed that S1 was mainly Fe 3 O 4 (75.30%), with KFeO 2 (24.50%) and minor γ -Fe 2 O 3 (0.20%). In contrast, S2 contained KFeO 2 as the major phase (55.72%), residual orthorhombic KNO 3 (37.28%) and rhombohedral KNO 3 (7.00%), with no refined magnetite, maghemite, or hematite contributions. The KFeO 2 crystallite size decreased from 169.62 Å in S1 to 116.52 Å in S2. Mössbauer spectroscopy indicated magnetic relaxation in nanosized KFeO 2 -rich domains and a more homogeneous hyperfine response for S2, whereas S1 was dominated by Fe 3 O 4 (70.5%) and a KFeO 2 -related relaxation contribution (26.0%). FTIR and Raman spectroscopy identified Fe–O modes and surface carbonate/hydroxylated species, while thermal analysis indicated adsorbed species and residual nitrate/carbonate compounds. TEM/HRTEM confirmed a refined S2 nanostructure, with an average particle/grain size of 3.97 ± 1.14 nm, compared with 19.31 ± 14.42 nm for S1. EDS/EELS confirmed the spatial association of Fe, K, and O and ionization features compatible with potassium-containing ferritic oxides. EPR supported magnetic relaxation/blocking behavior, with broad lines and effective g values of 2.12 (S1) and 1.72 (S2). Overall, precursor redesign increased the KFeO 2 fraction, suppressed secondary iron oxides, reduced crystallite size, and produced a more homogeneous nanostructure, although residual KNO 3 remains the main limitation to phase-pure KFeO 2 .