Detailed study of structural, optical, dielectric and electrical properties of Ni_0.7Cd_0.3Cr₂O₄ (NCCO) chromite prepared using sol-gel method

In this report, the new polycrystalline spinel-type chromite Ni_0.7Cd_0.3Cr₂O₄ (NCCO) was successfully synthesized by sol-gel process. This sample is characterized by X-Ray diffraction (XRD), optical analysis by DRS spectroscopy and dielectric measurements. The X-ray diffraction (XRD) analysis reveals that the prepared sample is well crystallized in the Fd3̅m space group. Optical results from the reflectance spectrum shows indirect band gap energy that was also evaluated from the reflectance spectra using the Kubelka-Munk function and Marotti’s approach, the E_gind is found close to 1.64 eV. The variations of Urbach energy (E_u), the penetration depth (δ), extinction coefficient (K) and refractive index (n) were clearly determined and discussed. The Ac impedance spectroscopy type Agilent model 4294 A was used to examine the dielectric and electrical transport properties over a wide temperature (200 K-400 K) and frequency range (100 Hz to100KHz). The obtained results demonstrate that the electrical conductivity (σ) correlates with the Jonscher power law that indicates a semiconducting behavior and confirm the ′′non-overlapping small polaron tunneling, ′′NSPT′′ model of our sample. The activation energy is estimated to be E_a = 0.529 eV based on the study of continuous conductivity. The behavior of permittivity (ε’,ε”) and the loss coefficient tgδ was attributed to Wagner’s Maxwell theory of interfacial polarization. The imaginary part of the impedance curve (Z′′) shows a dielectric relaxation phenomenon in the present compound. The Nyquist plots show a monotonic decrease in grain resistance (R_g) and grain boundary resistance (R_gb) with increasing temperature. This result confirms that the transport mechanism in the chromite NCCO is governed by the effect of grain boundaries. These analysis prove that our sample may be a good candidate for optoelectronics devices. Graphical Abstract: [Figure not available: see fulltext.]