The electrical transport properties of MgAl2−xCoxO4 (where x = 0.0, 0.5, 1.0, 1.5, 2.0) were investigated at room temperature. The dielectric behavior of the samples, and the contribution of the grains and the grain boundary regions to the electric response of the samples were observed using impedance spectroscopy in the frequency range of 20 Hz to 2 MHz. The DC conduction behavior was studied by measuring current density J against electric field E. It was observed that the grains and grain boundaries both contribute equally to the variation in electric response caused by changing the dopant concentration of cobalt in MgAl2O4. The combined Z″ and M″ spectroscopic plots indicated the presence of small polaron hopping conduction in the grain region of the samples. Moreover, the 25% doped sample showed minimum conductivity among all samples, which was two orders of magnitude less than that of the pure sample.
The infrared reflectivity spectra for potassium-doped polycrystalline magnesium aluminates Mg[Formula: see text]K[Formula: see text]Al2O4 (x=0, 0.25, 0.50, 0.75, 1) are measured in the frequency range between 10–15, 500 cm[Formula: see text] using FTIR spectrometer at room-temperature. Four optical phonon modes are observed in measured spectra, which are fitted by Lorentz oscillator model for semiconducting behavior and Lorentz–Drude model for metallic behavior. Moreover, optical parameters are also determined for these modes which may attribute to spinel structure for samples Mg[Formula: see text]K[Formula: see text]Al2O4, their reflectivity spectra shows a typical semiconducting nature. To study ionicity and effect of polarization, Born and Szigeti effective charges are calculated from longitudinal optical and transverse optical (LO–TO) splitting of modes for all samples. Optical bandgap has been estimated through optical conductivity ([Formula: see text]([Formula: see text])) and found to be x dependent.
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