1. PREPARATION OF ZINC-DOPED LANTHANUM STRONTIUM GALLATE SOLID ELECTROLYTE USING A REACTION-SINTERING PROCESS Yi-Cheng Liou*, Chung-Che Lan, Song-Ling Yang Department of Electronics Engineering, Kun Shan University, Tainan Hsien 71003, Taiwan, R.O.C. *Corresponding author. ycliou@mail.ksu.edu.tw La 0.8 Sr 0.2 Ga 0.8 Zn 0.2 O 2.8 (LSGZ) ceramics prepared using a reaction-sintering process was investigated in this study. Without any calcination involved, the mixture of raw materials was pressed and sintered directly. SrLaGa 3 O 7 is the major phase in 1150  C sintered pellets and decreased at higher sintering temperature 1250  C. La 0.8 Sr 0.2 Ga 0.8 Zn 0.2 O 2.8 became the major phase in pellets sintered at 1250 o C/2 h. Density of La 0.8 Sr 0.2 Ga 0.8 Zn 0.2 O 2.8 ceramics increases with sintering temperature and reaches a maximum 6.71 g/cm 3 at 1230 o C for 6 h. The reaction- sintering process has proven a simple and effective method in preparing La 0.8 Sr 0.2 Ga 0.8 Zn 0.2 O 2.8 ceramics for solid electrolyte applications in solid oxide fuel cells. The XRD patterns of LSGZ sintered at 1150 o C and 1250  C for 2 h are shown in Fig. 1. It can be seen reflections of SrLaGa 3 O 7, LSGZ, SrLaGaO 4 and La 4 Ga 2 O 9 were detected. SrLaGa 3 O 7 is the major phase in 1150  C sintered pellets and decreased at higher sintering temperature 1250  C. LSGZ became the major phase in pellets sintered at 1250 o C/2 h. Therefore, reaction-sintering process can efficiently transform the mixture of raw materials into LSGZ phase. La 4 Ga 2 O 9 phase decreased obviously at 1250 o C. Using a Pechini-type process, Tas et al. reported that SrLaGaO 4 and SrLaGa 3 O 7 phases appeared in the calcined La 0.9 Sr 0.1 GaO 2.95 at 1200 o C and disappeared at 1340 o C/6 h calcination. SrLaGa 3 O 7 phase appeared after 6 h calcined at 700 o C and about 4-5 wt% of a mixture of the undesired SrLaGaO 4 and SrLaGa 3 O 7 phases still remained even after calcined at 1400 o C for 6 h. They also found SrLaGa 3 O 7 as a major phase in LSGZ calcined at 1000 o C via aqueous chemical precipitation and almost pure LSGZ at 1200 o C. SEM photographs of as-fired LSGZ ceramics sintered at 1150-1250 o C/2 h are shown in Fig. 2. Porous pellet with fine grains of about 2 μm formed at 1150 o C and 1170 o C. This means 1150-1170 o C sintering is not high enough for grain growth and densification in LSGZ ceramics prepared using the reaction-sintering process. It can be easily observed that pores decreased at 1200oC and grain size increased at temperatures 1200-1250 o C. The amount of pores decreased in LSGZ ceramics sintered for 4 h as shown in Fig. 3. Dense LSGZ could be obtained at sintering temperatures above 1230 o C. Dense structure is needed in electrolyte of SOFC to avoid mixing and reaction between fuel and oxygen gas. Tas et al. reported LSGZ powders consisted of round particles with an average diameter of 0.25 μm after calcined at 1000 o C for 6 h. The non-compacted LSGZ powder body consisted of dense 20 to 30 μm chunks was observed at 1300 o C 6 h calcination. Fig. 4 shows the shrinkage percentage of LSGZ ceramics sintered at various temperatures for 2-6 h. It increases from about 19-22% at 1150 o C to 24-25% at 1250 o C. In our study of La 0.8 Sr 0.2 Ga 0.83 Mg 0.17 O 2.815 ceramics via reaction–sintering process, shrinkage of 17-20% at 1300oC and 26-28% at 1400 o C were found. It implies a lower temperature is needed in Zn-doped than in Mg-doped LaSrGaO 3-δ ceramics prepared via reaction-sintering process. In Fig. 5, density of LSGZ ceramics increases with sintering temperature and reaches a maximum 6.71 g/cm 3 at 1230 o C for 6 h. Fig. 3 SEM photographs of as-fired LSGZ ceramics sintered at (A) 1150 o C, (B) 1170 o C, (C) 1200 o C, (D) 1230 o C, and (E) 1250 o C for 4 h. Fig. 5 Density of LSGZ ceramics sintered at various temperatures for 2-6 h. Fig. 4 Shrinkage percentage of LSGZ ceramics sintered at various temperatures for 2-6 h. Fig. 1 XRD patterns of LSGZ sintered at (A) 1150 o C and (B) 1250 o C for 2 h. (1: LaGaO 3 ICDD PDF # 00-054-0870; 2: SrLaGaO 4 ICDD PDF # 01- 080-1806; 3:SrLaGa 3 O 7 ICDD PDF # 00-045-0637; 4: La4Ga 2 O 9 ICDD PDF # 00-037-1433) Fig. 2 SEM photographs of as-fired LSGZ ceramics sintered at (A) 1150 o C, (B) 1170 o C, (C) 1200 o C, (D) 1230 o C, and (E) 1250 o C for 2 h. Materials and Austceram 2007 July 4 - 6, 2007, Sydney, Australia