Structural, optical, electric and dielectric characterization of a NaCu0.2Fe0.3Mn0.5O2 compound

Abstract

The compound NaCu_0.2Fe_0.3Mn_0.5O₂ was synthesized using a solid-state method and it crystallized in a hexagonal system with a Rm space group in an O3-type phase. The optical properties were measured using UV-Vis absorption spectrometry to determine the absorption coefficient α and the optical band gap E_g. The optical band gap energy of this sample is 2.45 eV, which indicates that it has semiconductor characteristics. Furthermore, the electrical and dielectric properties of the material were investigated using complex impedance spectroscopy between 10⁻¹ Hz and 10⁶ Hz at various temperatures (333–453 K). The permittivity results prove that there are two types of polarization, dipolar polarization and space charge polarization. The Nyquist diagrams show the contribution of the effects of the grain, grain boundary, and electrode properties. The frequency dependence of the conductivity was interpreted in terms of Jonscher's law. The DC conductivity follows both the Mott and Arrhenius laws at low and high temperature, respectively. The temperature dependence of the power law exponent(s) suggests that the overlapping large polaron tunneling (OLPT) model is the dominant transport process in this material. The optimum hopping length of the polaron (4 Å) is large compared with the interatomic spacing (2.384 Å for Na–O and 2.011 Å for Cu, Fe, Mn–O).