Investigation of Structural and Electrical properties of cobalt-doped calcium nano ferrites suitable for chemical and gas sensor applications

Cobalt-substituted calcium ferrites (CCAFs) with compositions Co _x Ca _1–x Fe ₁₂ O ₁₉ (x = 0–0.25) were synthesised using the solution combustion method to examine their structural and electrical properties for chemical and gas sensing applications. X-ray diffraction confirmed the formation of a single-phase hexagonal magneto-plumbite structure, with crystallite dimensions increasing from 34.75 to 45.19 nm, indicating nanoscale grain growth following Co substitution. FTIR spectra showed typical metal-oxygen stretching vibrations at tetrahedral and octahedral sites. This showed that Co²⁺ ions had been successfully added to the ferrite lattice. SEM tests revealed that the nanograins were evenly distributed and had a porous structure, resulting in a large active surface area suitable for gas adsorption. Dielectric analysis revealed a high dielectric constant and loss at low frequencies that decrease as the frequency increases. This agrees with Maxwell-Wagner interfacial polarisation and the two-layer model of Koops, where conductive grains and resistive grain boundaries are responsible. The Verwey electron-hopping mechanism between Fe²⁺ and Fe³⁺ ions caused the AC conductivity to go up with frequency. Cobalt substitution made this even better. Complex impedance analysis revealed non-Debye relaxation behaviour, with relaxation times spanning from 0.2 to 1.99 µs. The materials also acted as semiconductors when the temperature went up. These combined structural, dielectric, and conduction properties demonstrate that CCAFs are suitable for chemical and gas-sensing applications that require stability, sensitivity, and affordability.