The Effect Of Single/Double Sintering Aids On The Structure And Properties Of Gd_0.2Ce_0.8O_2-δ（GDC） And GDCSi

Dense solid oxide electrolyte is one of the main components of SOFC.CeO₂-based electrolytes have been investigated mainly owing to their high ionic conductivity and outstanding compatibility with a variety of electrode materials.Nevertheless,high sintering temperature might result in poor compatibility between components,interface reactions and high manufacturing costs,which limits the development of CeO₂-based electrolytes.The negative effect on the GDC grain boundary came from the enrichment of the Si O₂impurities in the grain boundary.The metal oxides were added as sintering aids and grain boundary scavengers in CeO₂-based electrolytes.The metal oxides could reduced the sintering temperature and improved the densification of CeO₂-based electrolyte.Morever,the conductivity was increased by adding metal oxides.In this paper,a solid state mixing method was used to prepare x ESB-GDC（x=0-5wt.%）composite electrolyte materials.Sol-gel method was used to prepare Gd₂O₃ doped CeO₂(Gd_0.2Ce_0.8O_2-δ,GDC)Electrolyte.Er_0.2Bi_0.8O_1.5（ESB）as sintering aids and its composite effect with GDC were studied.The effects of the addition of MgO/Fe₂O₃sintering aids on the sintering behavior,microstructure and conductivity of GDC and GDCSi(Gd_0.2Ce_0.8O_2-δ+500 ppm Si O₂)electrolytes were investigated.The results show:（1）An appropriate level of ESB was added to the GDC increased the effective densification of the samples and reduced theσ_gi,σ_gb andσ_t of the samples.The doping of ESB was able to improve the densification of electrolyte and generate more oxygen vacancies.It should be noticed that 4 wt.%ESB doping could result in the highestσ_gb andσ_t.At 450°C,theσ_gb andσ_t of the composite were 9.23 and 3.12 times higher than GDC,respectively.（2）A small level of sintering aids MgO and Fe₂O₃ were added to GDC electrolyte alone or in combination.Without changing the crystal structure,the sintering temperature of the GDC electrolyte could be reduced by adding a small level of sintering aids MgO and Fe₂O₃.At the same time,the relative density and the conductivity of electrolytes were improved.Furthermore,the GDC electrolyte co-doped with MgO and Fe₂O₃（GDC-MF）had a more obvious effect than the GDC doped with MgO or Fe₂O₃ single sintering aid.In the same condition,GDC-MF had higher density and electrical properties.GDC-MF had the highestσ_gb andσ_t.At 400℃,theσ_gb andσ_t of GDC-MF were 15.89 times and 5.56times that of GDC.（3）The Fe₂O₃ and MgO incorporation in the Gd_0.2Ce_0.8O_2-δ+0.05%（ω）Si O₂（GDCSi）could reduce the sintering temperature and improve the conductivity ofσ_gb.The addition of4 mol%MgO,4 mol%Fe₂O₃ and 2 mol%MgO-2 mol%Fe₂O₃ could promote the grain growth of the GDCSi system and reduced the inter-grain porosity.It is of interest that 2mol%MgO-2 mol%Fe₂O₃ co-doped GDCSi-MF resulted in the highestσ_gb andσ_t.At400°C,theσ_gb andσ_t of the GDCSi-MF were 10.41 and 1.82 times higher than GDCSi,respectively.