Materials Science and Engineering A 383 (2004) 229–234 Carbonate Co-precipitation of Gd 2 O 3 -doped CeO 2 solid solution nano-particles A.I.Y. Tok ∗ , L.H. Luo, F.Y.C. Boey School of Materials Engineering, Nanyang Technological University, Nanyang Avenue, Singapore Received 4 March 2004 Abstract This paper reports on the synthesis of 20 mol% Gd 2 O 3 -doped CeO 2 solid solution (20 GDC) nano-particles via carbonate co-precipitation. Precursors and calcined particles were characterized using TGA, XRD, BET, FESEM, and TEM. From the diffraction pattern using XRD with TEM, it was shown that the Gd 3+ replaced the Ce 4+ lattice in the fluorite structure (FCC) of CeO 2 , as opposed to it being a second phase in the CeO 2 structure. The 20 GDC particles were calcined at 700 ◦ C for 2 h, and sintered to >99% density at a very low sintering temperature of 1150 ◦ C for 4 h. © 2004 Elsevier B.V. All rights reserved. Keywords: Gd 2 O 3 -doped CeO 2 ; Carbonate co-precipitation; Nano-particles; Solid oxide fuel cells; Microstructure; Solid solution 1. Introduction Gadolinium oxide-doped fluorite structured cerium ox- ide, 20 mol Gd 2 O 3 –CeO 2 (hereafter referred to as 20 GDC for convenience), is a solid solution formed by replacing the Ce 4+ sites of the CeO 2 lattice by Gd 3+ cations. 20 GDC has been recognized as a low temperature (500–700 ◦ C operating temperature) electrolyte material for applications in solid-oxide fuel cells (SOFC), as GDC has higher ionic conductivity compared to other com- monly used materials such as YSZ[(ZrO 2 ) 0.9 (Y 2 O 3 ) 0.1 ] and LSGM(La 0.9 Sr 0.1 Ga 0.8 Mg 0.2 O 2.85 ) [1]. 20 GDC powders synthesized via current solid-state reactions require very high sintering temperatures (1700–1800 ◦ C) [2]. Traditional ball milling of particles to reduce its size will also introduce impurities such as silicon into the 20 GDC particles, and this will severely decrease its ionic conductivity since silicon form an insulation glassy phase in the grain boundaries [3]. A lower electrolyte sintering temperature is also desired, as the cathode and anode materials are normally sintered at a relatively lower temperature of 1100–1300 ◦ C [4]. There- fore, an electrolyte material that can be co-fired together with the anode/cathode at a lower temperature would be desired. In addition, nano-particles can impart improved ∗ Corresponding author. Tel.: +65 67904935; fax: +65 67904935. E-mail address: miytok@ntu.edu.sg (A.I.Y. Tok). mechanical properties to the electrolyte layer, as compared to those consolidated from micron-sized particles. Several types of wet-chemical methods have been re- ported for the synthesis of 20 GDC particles. These include oxalate co-precipitation [5], sol–gel [6], and hydrothermal treatment [7]. These wet chemistry-derived powders gener- ally show better reactivity than those obtained via solid-state methods, but they still require relatively high densification temperatures of about 1400–1600 ◦ C to reach 99% density. The limitation here seems to stem from severe agglomera- tion of the particles, and undesirable morphologies of the resultant particles. The use of carbonates as the precursor materials for highly sinterable oxides has shown characteris- tics of being non-gelatinous, and exhibit significantly weaker agglomeration after drying [8]. It was also reported that reactive Ce 0.8 RE 0.2 O 1.9 (RE = La, Nd, Sm, Gd, Dy, Y, Ho, Er, and Yb) powders synthe- sized via carbonate co-precipitation required an aging tem- perature of 70 ◦ C and drying in N 2 [9], as opposed to using room temperature aging and air-drying. 2. Experimental procedure 2.1. Powder synthesis Starting materials used for the 20 GDC synthesis were cerium nitrate hexa-hydrate and gadolinium nitrate 0921-5093/$ – see front matter © 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.msea.2004.05.071