Tunable structural and vibrational properties of magnesium-doped Ba(Mn1−x Mgx)O3−δ oxides: Insights from structure, refinement, magnetism, and Raman spectra

Perovskite-type (ABO3−δ) oxides provide a versatile platform to explore charge–spin–orbital–lattice interactions with wide-ranging technological applications. In this work, magnesium-doped Ba(Mn1−xMgx)O3−δ (x = 0–0.08) oxides were synthesized via a cost-effective sol–gel route using metal nitrates and oxalic acid precursors. It exhibits a hexagonal structure (space group R 3̄ m) for undoped (x = 0) and dual “hexagonal + orthorhombic” phases for magnesium-doped oxides for x = 0.02–0.08. The lattice parameters of the hexagonal phase decrease with magnesium content (x) as ah = bh ~ 5.714 Å, ch ~ 21.472 Å (ar ~ 7.881, α ~ 42.51° in rhombohedral axis) for {x = 0} to ah = bh ~ 5.708 Å, ch ~ 21.450 Å (ar ~ 7.878, α ~ 42.53° in rhombohedral axis) for {x = 0.08}, accompanied by total cell volume reduction. Similarly, the orthorhombic unit cell volume decreases (~876.2–866.3 Å3) with magnesium substitution due to charge compensation, while the average bond length increases (~2.639–2.910 Å), indicating lattice distortion. These structural changes confirm the incorporation of Mg2+ into the lattice and its influence on the crystal framework. Raman peak at ~318.7 cm−1 (for x = 0) shifted toward lower wavenumber side along with the decrease in peak intensity. Bands, in the 550–800 cm-1 range, are attributed to A1g symmetric stretching of BO6 octahedra and oxygen vacancy-related modes, confirming octahedral distortions. The M–H curves display narrow hysteresis with low Hc (~61–76 Oe) and Mr (~9.3–10.7 × 10−4 emu/g), confirming the absence of long-range ferromagnetism. The saturation magnetization decreases sharply with Mg2+ substitution due to disrupted Mn–Mn exchange, but partially recovers at higher doping (x = 0.08) owing to stabilization of mixed Mn3+/Mn4+ states via oxygen non-stoichiometry. Presence of anion vacancies and related properties suggests the material’s suitability for technological applications, e.g., fuel cells, catalyst, and membrane.