Grain growth correlated complex impedance spectroscopy, modulus spectroscopy and carrier hopping mechanism in MnCo2O4: Influence of sintering temperature

This work primarily focuses on grain growth dependent electrical properties of spinel nano-cobaltite MnCo2O4 prepared by co-precipitation method and sintered at different temperatures between 400 and 1000 degrees C. XRD confirms formation of cubic manganese cobaltite. Rietveld method was used to estimate different microstructural parameters. Crystallite size increases with increasing sintering temperature from similar to 12.18 nm to similar to 97.95 nm which is comparable with grain growth noticed from FESEM micrographs. TGA-DSC curve shows long range phase stability of the materials. Cole-Cole plot obtained from complex impedance spectroscopy analysis shows non-Debye type depressed semi-circular nature. Activation energies evaluated from ac conductivity, migration energy and relaxation time approaches are consistent with each other indicating that the charge carriers have same barrier potential for conducting, migrating and relaxing. Hopping mechanism of charge carriers was confirmed from ac conductivity analysis. Conductivity is higher for sample sintered at higher temperature which might be associated with lowering of inter granular hopping distance. Master curves show good scaling behaviour of different spectra. It depicts that time-temperature superposition principle (TTSP) is valid for the samples and conduction mechanism is same at all temperatures.