Engineering Multicationic Pathways for Next-Gen Dielectric and Thermistor Applications

Abstract

In this study, a novel multicationic spinel system Cd_0.6Mg_0.2Cu_0.2Co_2-xFe_xO₄ (x = 0, 0.5, 1.0, 1.5) was synthesized via a sol–gel method and systematically investigated for its structural, chemical, and dielectric properties. XRD and Rietveld refinement confirmed a single-phase cubic spinel structure across all compositions, while XPS and Raman spectroscopy revealed the evolution of Fe³⁺/Fe²⁺ and Co³⁺/Co²⁺ redox pairs with increasing Fe content, enabling tunable polaronic conduction. Dielectric analyses, including impedance, electric modulus, and AC conductivity, demonstrated thermally activated relaxation governed by small polaron hopping, with a progressive shift from overlapping large polaron tunneling (OLPT) to non-overlapping small polaron tunneling (NSPT) mechanisms. Fe substitution significantly enhanced dielectric response and conductivity, reducing activation energy and relaxation time. Additionally, thermistor parameters (β, TCR, α) indicated high thermal sensitivity and negative temperature coefficient behavior, suggesting potential for temperature sensing applications. These findings underscore the synergistic role of multicationic doping and Fe-mediated conduction in optimizing dielectric and thermoelectric performance in spinel ferrites.