Abstract
Spinel-type novel compositions of mesoporous ternary metal oxides ZnFeNiO4 (ZFNO) and CoFeNiO4 (CFNO) microspheres were synthesized through a facile hydrothermal method with post calcination approach. X-ray powder diffraction and X-ray photoelectron spectroscopy studies reveal the phase pure spinel-type cubic crystal formation. Electron microscopic studies show the mesoporous microspheres were constructed by the porous nano-lamellae which are formed by the nanoparticles. Specific surface area of ZFNO and CFNO is found as 107 and 28 m2 g−1 with maximum pore diameter of 4 and 3 nm respectively. The optical Eg of ZFNO and CFNO is found to be 2.21 and 1.98 eV respectively. Impedance spectroscopy is used to study the electrical properties of the samples in the temperature range of 150–600 °C. The conductivity of CFNO is higher than that of ZFNO. The activation energy of conductivity is found to be 0.67 and 0.42 eV for ZFNO and CFNO respectively. Isothermal AC conductivity were analysed with Koops theory and Jonscher's power law. Frameworks of various theoretical models are considered in order to explain the frequency and temperature dependent conductivity. It is observed that the quantum mechanical tunnelling mechanism is consistent for conductivity's frequency exponent of ZFNO and only below 330 °C for CFNO.
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