Dielectric relaxation, AC conductivity behavior and its relation to microstructure in mechanochemically synthesized Mn-doped CeO2 nanocrystals

Abstract

A simple mechanical alloying process has been implemented to obtain cerium oxide nanocrystallites monodoped with transition metal element (Mn). The microstructural, compositional and crystallographic information are investigated by employing Rietveld refinement using X-ray diffraction (XRD) data, energy dispersive X-ray (EDX) pattern and analyzing high resolution transmission electron microscopy (HRTEM) images. The results reveal that the sample exhibits a single phase cubic fluorite-type Ce0.95Mn0.05O2-δ structure. Rietveld analysis shows the coexistence of Ce3+ and Ce4+ ions in the sample. HRTEM image reveals the sheer plastic deformation on lattice planes. The frequency and temperature dependent electrical behavior of the undoped, Mn-doped and sintered samples are analyzed by impedance spectroscopy, dielectric relaxation and ac conductivity studies. The correlated barrier hopping (CBH) model has well explained the ac conduction mechanism. The release of electrons during the reduction of Ce4+ and/or Mn4+ ions to Ce3+ and/or Mn3+/Mn2+ ions by the exclusion of excess oxygen in the lattice are responsible for the electronic conductivity of the samples. The activation energy of the sintered sample is estimated both from relaxation and hopping processes and the estimated values ascertain that the charge carrier hopping process in the samples is accompanied by the dielectric relaxation.