Effect of the synthesis conditions of Ce0.9Gd0.1O1.95 powder on its morphology and characteristics of the oxygen ion-conducting ceramics obtained by spark plasma sintering

Abstract

In this work, Ce0.9Gd0.1O1.95(10GDC) powders were synthesized by thermal decomposition of oxalate precursor crystals Ce1.8Gd0.2(C2O4)3·10H2O having a plate shape. The morphology of the oxide was found to be strongly influenced by the dehydration conditions of the precursor crystals. Dehydration in air at 125 °C led to the formation of the product in a pseudomorph form, retaining the shape of the precursor crystals and showing only slight dimensional changes. The formation of a pseudomorph was accompanied by a loss of crystallinity. When dehydration occurred at an increased water vapor pressure at the same temperature, a crystalline product formed having a significantly altered morphology. Unlike dehydration in air, after which the crystals retained their shape, an intensive shattering of the crystals occurred upon dehydration at an increased water vapor pressure. Structural transformations during dehydration were shown to determine the product morphology. The 10GDC powders with different textural characteristics were obtained by oxidative thermolysis (at 300 °C) of dehydration products. The oxide powders were sintered by spark plasma sintering at a temperature of 1100 °C and a pressure of 40 MPa. The microstructure, relative densities, and conductivities of the ceramic samples obtained from powders of two different morphologies were compared. The sintered ceramic samples had comparable grain size (<1 μm); however, the material obtained from the crystalline product of dehydration showed a higher relative density. The ionic conductivity of the ceramic material obtained using the crystalline product of dehydration was almost one order of magnitude higher than that of the sintered material obtained from the poorly crystallized product of dehydration.