Structural evolution, charge transport, hopping conduction, and electrochemical response of Co ²⁺ substituted spinel ferrites

Abstract Electrochemical and temperature-dependent transport studies of Co-doped Ni ferrite nanoparticles, Ni 1− x Co x Fe 2 O 4 ( x = 0.1 and 0.9) were prepared using a simple auto-combustion method. FTIR spectra exhibit characteristic tetrahedral and octahedral sites, with an average force constant of 1.910 × 10 5 dyne cm −1 , confirming strong metal-oxygen bonding in the spinel ferrite structure. X-ray diffraction results indicate an average crystallite size of approximately 33–38 nm, consistent with morphological features observed in SEM micrographs. X-ray photoelectron spectroscopy spectra confirm the presence of Ni 2+ , Co 2+ , and Fe 3+ ions in the NC ferrite nanoparticles. Electrical properties were analysed over various frequencies and temperatures. The NC ferrite nanoparticles exhibited frequency-dependent behaviour, relaxation dielectric response and thermally activated characteristics, indicating their semiconducting nature. The frequency dependence of AC conductivity at various temperatures follows Jonscher’s power law, with conductivity 1.003 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mo>×</mml:mo> </mml:mrow> </mml:math> 10 −5 S cm −1 at 453 K (NC-1). NC-1 sample exhibited the best dielectric performance and conductivity, likely due to efficient charge transport via polaron hopping between mixed valence states. The electrochemical investigations revealed a reversible and stable capacitive behaviour, as evidenced by quasi-rectangular cyclic voltammetry profiles and consistent impedance response. Overall, the NC ferrite nanoparticles have potential applications in multifunctional electronic applications.