NaCa2FeMn2O5

NaCa2FeMn2O5 is a mixed‑valence transition‑metal oxide that belongs to the family of layered perovskite‑derived structures. The formula reflects a composition of one sodium (Na), two calcium (Ca), one iron (Fe), two manganese (Mn), and five oxygen (O) atoms per formula unit. Synthesis is typically performed by solid‑state reaction of oxides or carbonates of the constituent metals, heated under an oxygen atmosphere at 950–1100 °C. In some reports, a sol‑gel route has been used to improve homogeneity and reduce particle size. The resulting material is a dense polycrystalline powder composed of plate‑like crystallites.

The crystal structure is orthorhombically distorted from the ideal perovskite archetype, with the Na+ ions occupying interlayer sites between rock‑salt Ca2FeMn2O5 slabs. The Fe and Mn cations occupy octahedral positions within the slabs, with mixed valence states (Fe3+ / Fe4+ and Mn3+ / Mn4+) that give rise to electronic conductivity and magnetic interactions. Neutron diffraction and X‑ray diffraction studies indicate a layered arrangement where the conductivity pathway is largely two‑dimensional, lying in the ab‑plane of the orthorhombic lattice.

Physically, NaCa2FeMn2O5 exhibits reversible Na‑ion intercalation chemistry. Cyclic voltammetry shows redox couples near 4.0 V versus Na/Na+, attributable to Fe3+/Fe4+ and Mn3+/Mn4+ transitions. When evaluated as a cathode material in Na‑ion batteries, the oxide delivers initial capacities around 140 mAh g⁻¹ and retains more than 85 % of capacity after 200 cycles at 0.1 A g⁻¹. The presence of calcium enhances structural stability during Na‑ion insertion/extraction, reducing lattice strain compared with binary Fe–Mn oxides.

Magnetically, the material displays antiferromagnetic ordering below 150 K, with a weak ferromagnetic component appearing at lower temperatures due to canting. The mixed valence and layered geometry also give rise to notable electronic conductivity improvements upon partial reduction, making NaCa2FeMn2O5 a candidate for mixed‑conducting applications such as solid‑state electrolytes or multifunctional oxides.

In summary, NaCa2FeMn2O5 is a layered mixed‑metal oxide offering promising electrochemical performance as a Na‑ion battery cathode, coupled with intriguing magnetic and structural properties that arise from its mixed valence and interlayer sodium chemistry.