Low-temperature fabrication and electrical property of 10 mol% Sm₂O₃-doped CeO₂ ceramics

Ten mol% Sm2O3-doped CeO2 solid-solution (20SDC) powders have been synthesized via carbonate coprecipitation using ammonium hydrogen carbonate (AHC) and urea as the precipitants, respectively. Characterizations were achieved by elemental analysis, X-ray diffractometry, differential thermal analysis/thermogravimetry, and FESEM. An amorphous hydroxyl carbonate precursor (Ce,Sm)(OH)CO3·2H2O having nanosized (~10 nm) spherical particles was formed with AHC, while a mixture of crystalline (Ce,Sm)2(CO3)2(OH)2·H2O and (Ce,Sm)2O(CO3)2·H2O phases exhibiting irregular particle morphologies was obtained with urea. Both the precursors convert to oxide solid solutions without any phase detected corresponding to Sm2O3 during calcination. The oxide powder processed via the AHC method can be sintered to >99% of the theoretical at a low temperature of 1200 ˚C, due to the good dispersion and ultrafine size (~15 nm) of the particles, while that from the urea method can only reach ,67.2% dense at the same temperature. Electrical conductivity of the densified ceramic was measured in air in the range 400—700 ˚C by the DC three-point method, and an activation energy of ~60.5 kJ/mol was derived from the experimental data.© 2003 Elsevier Ltd. All rights reserved.