Microstructure correlated electrical conductivity of Manganese alloyed nanocrystalline cubic zirconia synthesized by mechanical alloying

Abstract

Fully stabilized cubic (c) ZrO2 phase has been synthesized by mechanical alloying (MA) the stoichiometric powder mixture of elemental Mn (5–20mol%) and monoclinic (m) ZrO2 at room temperature. XPS study reveals that major part of metallic Mn is ionized to Mn2+ oxidation state during MA. Mn-alloyed c-ZrO2 nanoparticles with ∼18nm particle size have been synthesized within 10h of MA. Microstructures of the compounds have been precisely evaluated by analyzing the X-ray powder diffraction patterns employing Rietveld refinement and transmission electron microscopy images. A decrease in lattice parameter from 5.11Å to 5.09Å is correlated with an increase in oxygen vacancy from 14% to 26% with increasing Mn concentrations. Elemental compositions in the compounds are obtained from electron probe microanalysis. The role of Mn alloying in the polymorphic phase transformation (m→c) has been established with changes in structure and microstructure parameters. Electrical conductivities of all c-ZrO2 compounds are measured in the temperature range 350–550°C. Grain and grain boundary contributions to total conductivity are calculated from frequency dependent real and imaginary impedance. Conductivity of Mn alloyed c-ZrO2 increases with increasing temperature and Mn concentrations. Electrical transport mechanism in the compound is studied by impedance and modulus spectroscopy. The relaxation frequency is found to be temperature, microstructure and composition dependent.