Microstructural, Mossbauer, thermal and dielectric studies of ZnFeCoO4 spinel oxide for optoelectronic applications

In this article, we have investigated the structural, Mossbauer, thermal and dielectric properties of the ZnFeCoO4 spinel oxide elaborated using the sol-gel process. We have used X-ray diffraction (XRD) and scanning electron microscopy (SEM) to analyze the microstructural properties of our sample. The XRD pattern shows the formation of the ZnFeCoO4 compound as the main phase, matched with the cubic spinel structure, as well as a secondary phase of ZnO was also identified. The SEM micrograph shows the spherical shape of grains with porosity. The Raman spectra reveal five Raman active optical modes (A(1g) + E-g + 3T(2g)), confirming the spinel structure of the prepared sample. The electrical conductivity measurements were analyzed using Jonscher universal power law s (?) =s(dc) + A?(p). The temperature dependence of the exponent p suggests that the non-overlapping small polaron tunneling model (NSPT) is the appropriate conduction mechanism within the synthesized sample. The variation of dielectric permittivity is explained in terms of interfacial polarization based on the Maxwell-Wagner theory. The plots of the imaginary parts of the modulus (M'') reveals two specific relaxation frequency shifted to higher frequencies with increasing temperature. The activation energies deduced from the dc conductivity and electrical modulus are comparable implying that the relaxation and conduction processes are caused by the same type of charge carriers. Nyquist plots (Z'' vs. Z') were well adjusted using an equivalent circuit that includes both grain and grain boundary response, hence, the equivalent circuit configuration is a type of [(R-g//CPEg) + (R-gb//CPEgb)].