Electrical behavior of Gd-doped CeO2 electrolyte ceramics sintered from nanopowders prepared by mechanical alloying process

Abstract

The densification behavior of nanocrystalline Gd-doped ceria electrolyte, synthesized via mechanical alloying process, was investigated by means of the conventional pressure less sintering and the two-step sintering methods. The effect of the heating rate and the amounts of dopant on the sinterability of Ce1−x Gd x O(2−δ) x = 0.2 (2GDC) and x = 0.3 (3GDC) oxides was studied, which indicated that the gadolinium retards densification and grain growth in the final state of the conventional sintering and 2GDC samples reach 94% density at 1,550 °C. Subsequent investigation on the grain growth in the fully densified ceramics showed that lowering of the heating rate and increasing of the soaking time reduce the effect of dopant and cause samples to be densified to the higher theoretical density (97%) at lower temperatures (1,400 °C). Fully dense Gd-doped ceria ceramics with finest grain size (900–1,100 nm) can be obtained by two-step sintering method. Electrical conductivity measurement in the GDC samples was studied by impedance spectroscopy. The grain boundary conductivity in these specimens obtained by two-step sintering method was compared with normal sintered specimens. It is concluded that the reduced conductivity observed in the two-step sintering specimen is attributable to the microstructure changes obtained by increased of grain boundary resistivity.