Correlating oxide ion conductivity with ionic size of dopant and defect structures in ThO2-LnO(1.5) (Ln = Y, La and Gd) prepared by modified epoxide gel method

摘要

Up to 60, 50 and 50 mol% of Gd3+, Y3+ and La3+ ions could be dissolved in thoria retaining fluorite structure following a modified epoxide mediated sol-gel synthesis and verified from powder X-ray diffraction and electron microscopy measurements. In addition to the T-2g vibration mode due to fluorite structure, oxygen vacancy defect bands emerged in their Raman spectra whose intensity was found to be sensitive to the ionic size of aliovalent ion. Significant enhancement in the oxygen ion conductivity has been observed for thoria samples loaded with aliovalent ions (373-773 K). Among them, Th0.5La0.50O2-delta exhibited the highest conductivity. Breakdown in the centre of symmetry of the crystallography site of lanthanide ion arising from the distortion in LnO(8) units was noticed when probed by doping with luminescent active, Eu3+. The strength of ion hopping process operative in these systems was deduced from fitting the data using Jonscher empirical relation.