Study of high-temperature dielectric response and AC conduction mechanism of Sr7Mn4O15 compound

This study explores the dielectric properties and AC conductivity of Sr₇Mn₄O₁₅ over 20 Hz–2 MHz and room temperature to500 °C. Single-phase Sr₇Mn₄O₁₅ was synthesized via a ceramic route, and Rietveld refinement of XRD data confirmed a monoclinic structure (P121/c1) with lattice parameters: a = 6.8165 Å, b = 9.6247 Å, c = 10.3864 Å, α = γ = 90°, and β = 91°. The optical band gap, determined from UV–Vis-IR spectra (200–1200 nm), is 1.58 eV. A high dielectric constant at low frequencies is attributed to interfacial polarization at grain boundaries. Relaxor-like behavior was observed in the ε_r' vs. T curve. AC conduction follows the non-overlapping small polaron tunneling (NSPT) model. Impedance (Zʺ) curves indicate a single relaxation phenomenon, with approximately equal activation energies for DC conduction and relaxation suggesting a common mechanism. XPS analysis showed Mn exists as Mn³⁺/Mn⁴⁺ and Sr as Sr²⁺.