Structural, theoretical, and experimental study of AC electrical conduction mechanism and thermodynamic properties of Cu_0.6Cd_0.4Cr₂O₄ spinel oxide

In this work, Cu_0.6Cd_0.4Cr₂O₄ spinel oxide was synthesized by means of sol–gel auto-combustion route. The refined X-ray powder diffraction pattern confirmed the single-phase formation of the material, which crystallized in a cubic spinel structure with space group Fd-3 m. The alternating current conduction mechanism and modulus behavior of this sample were investigated over a broad frequency range (from 100 Hz to 1.6 MHz) for various temperatures ranging from 300 to 660 K. Two equivalent circuit models, R//C//CPE below 440 K and above this temperature R₁//C₁//CPE₁ in series with R₂//CPE₂, were applied to fit the impedance data. The temperature dependence of the direct current conductivity could be described in terms of Arrhenius relation with four activation energies, 1.8 eV, 0.76 eV, 0.80 eV, and 0.98 eV, in regions I (T < 360 K); II (360–420 K); III (440–500 K); and IV (T > 500 K), respectively. The temperature and frequency dependence of AC conductivity was found to satisfy Jonscher’s law (developed) at different temperatures. The variation of the exponent “s” with temperature strongly suggests that the conduction mechanism takes place by correlated barrier hopping (CBH) model in each region. A theoretical study of (AC) electrical conduction in this material has been interpreted using Elliot’s theory, and Elliot’s parameters are determined. For the modulus formalism, the extracted activation energies from the linear fit of ln(fp) as a function of 1000/T match well with those obtained from DC conductivity confirming that transport mechanisms were based on hopping phenomena.