Observation of large dielectric permittivity and dielectric relaxation phenomenon in Mn-doped lanthanum gallate

Polycrystalline LaGa_1-xMn_xO₃ (x = 0, 0.05, 0.1, 0.15, 0.2 and 0.3) samples were prepared via the solid-state reaction method. These samples were characterized using synchrotron-based X-ray diffraction (XRD) and the X-ray absorption near edge structure (XANES). XRD studies confirm the orthorhombic structure for the prepared samples whereas XANES analysis reveals the co-existence of Mn³⁺ and Mn⁴⁺ in all Mn-doped samples. Dielectric relaxation is observed for all Mn-doped samples whereas a large dielectric constant (ε′) is perceived in samples with higher Mn doping (x = 0.2 and x = 0.3). Occurrence of a large ε′ is attributed to the huge decrease in impedance with increasing Mn doping which is governed by the hopping charge transport and extrinsic interface effects, whereas at high frequencies, this effect is observed possibly due to dipolar effects associated with the possible off-centrosymmetry of the MnO₆ octahedron which is indicated by the pre-edge feature (Mn K-edge) in XANES and validated through P-E measurements. The appearance of dielectric relaxation was credited to the dipolar effects associated with the flipping of the Mn³⁺/Mn⁴⁺ dipole i.e., with the hopping of charge carriers between Mn³⁺ and Mn⁴⁺ under an external electric field. The value of activation energy (E_a = 0.36 eV), extracted from temperature-dependent dielectric data, reveals the polaron hopping mechanism.