Structural and dielectric properties of the fluorite-type LaxCe1-xO2-δ ceramics

High density (95-97%) LaxCe1-xO2-delta (x = 0.1, 0.2) ceramics were tested for structural and dielectric properties. Dense microstructure and controlled phase-purity were obtained for all the La3+-doped samples. A surprising three-fold increase was noticed in the frequency dependent dielectric permittivity is an element of(r)(f) behavior for the La0.2Ce0.8O2-delta ceramic, associated with the space-charge polarization at grain boundaries or inhomogeneous microstructure of the ceramic. High resistivity (similar to 10(8) Omega m) at room temperature was noticed for the ceramics (at 100 Hz). Hopping of electrons within the oxygen vacancies were noted as the main transport mechanism; strong localization of charge carriers were noticed at high frequencies. The temperature dependent ac-resistivity analysis rho(ac)(T) provides strong evidence for Mott's variable range hopping process of charge carriers, between the localized states with an average hopping length of R-H of 3 nm and hopping energy of W-H of 0.67 eV. Moreover, the effect of grains and grain boundaries on the correlation between ac-conductivity sigma(ac) and angular-frequency omega has been discussed in detail.