Structural, Dielectric, and Energy Storage Properties of Citric Acid and Ethylene Glycol Assisted Hydrothermally Synthesized Y 2 FeCoO 6

Citric acid and ethylene glycol assisted hydrothermal synthesis of pure‐phase double perovskite oxide Y 2 FeCoO 6 is reported. The Rietveld refinement confirm the orthorhombic phase formation with Pnma space group symmetry and lattice parameters as, a  = 5.5039 Å, b  = 7.4734 Å, and c  = 5.2094 Å. The high‐resolution transmission electron micrographs exhibit formation of flakes, composed of agglomerated crystallites, oriented in [121] direction. The oxidation states of Fe as Fe 3+ and Co as Co 2+ /Co 3+ are observed by X‐ray photoelectron spectroscopy. The room temperature relative permittivity, 6.8 × 10 4 , is found to increase to 1.3 × 10 7 at 473 K and frequency 500 Hz. The specific capacitance of ≈31.32 F g −1 is obtained at the current density of 1 A g −1 . The effective charge storage involve the redox reactions of Fe 2+ /Fe 3+ , Co 2+ /Co 3+ , and Co 3+ /Co 4+ , and excellent capacitance retention of ≈99% is achieved after 5000 charging/discharging cycles at current density of 6 A g −1 .