Synergistic fabrication and investigation of the structural, morphological, electrical, and dielectric properties of Fe0.01Zn0.99O@C core shell structures: Towards an in-situ energy storage application

Semispherical and semi-hexagonal Fe0.01Zn0.99O@C core–shell structures are synthesized using a hydrothermal method. Their morphology is examined through FESEM and transmission electron microscopy, which clearly highlights the roles of grains and grain boundaries in defining the overall microstructural characteristics of the material. The polycrystalline nature of the freshly prepared sample is confirmed through the FullProf‑refined XRD spectrum, which reveals an average crystallite size of D = 23 ± 0.2 nm. Furthermore, comprehensive temperature-dependent impedance spectroscopy is performed to investigate the electrical response of the material and to distinguish the individual contributions arising from different electroactive regions, such as grains, grain boundaries, and interfaces. The temperature-dependent dielectric analysis reveals colossal permittivity (ε′ > 10³) in the range of 278–433 K, accompanied by a remarkably low tangent loss (~0.02) across the applied frequency window of 1 Hz to 10⁷ Hz. A pronounced increase in AC conductivity with temperature is observed, rising from 5.9 × 10⁻⁸ S·cm⁻¹ to 1.5 × 10⁻⁵ S·cm⁻¹, and the behavior is well described by the correlated barrier hopping (CBH) model. The temperature-dependent physical parameters, including binding energy, barrier height, and minimum hopping distance, are systematically evaluated and thoroughly elucidated in this study. The AC conductivity, together with the enhanced dielectric characteristics, demonstrates that this material is highly suitable for practical applications in energy‑storage systems and advanced electronic devices. Furthermore, the optical properties are examined through diffuse reflectance spectroscopy (DRS), and the observed redshift in the band gap (Eg~3.17 eV) is determined using the Kubelka–Munk (KM) formalism. This comprehensive analysis encompasses the frequency‑ and temperature-dependent dielectric behavior make this material suitable for energy storage devices.