The Study of Extrinsic-Doped LaGaO3 Solid Electrolyte

• Main Authors: Chang-Tse Hsieh, 謝昌哲
• Other Authors: Wen-Ku Chang
• Format: Others
• Language: zh-TW
• Published: 2003
• Online Access: http://ndltd.ncl.edu.tw/handle/43108361439784806891

碩士 === 國立東華大學 === 材料科學與工程學系 === 91 === Abstract Solid state electrolyte lanthanum gallate of the perovskite structure type has been investigated as the replacement for yttria-stabilized zirconia ,YSZ with its low resistivity and almost completely ion conductivity (ti=1). Due to solid oxide fuel cell (SOFC) is operated at high temperature, solid electrolyte also needs good stability in crystal structure for long time heat treatment. In this study, various concentration of aliovalent dopants, SrCO3 and MgO , are adopted for extrinsic doping in LaGaO3 to substitute A、B site ions of La3+ and Ga3+ in order to obtain higher concentration of oxygen vacancy. It makes oxygen ions migrate through the lattice more easier, thus enhances the electrical conductivity of doped lanthanum gallate. The relationship between dopant concentration and the effects upon crystal structure and the conductivity of doped LaGaO3 is extensively researched in the study. Within the solubility range (Sr2+ ~7 mol%, Mg2+ ~4mol%), the larger magnesium and strontium ions solutes in LaGaO3 completely, and we observe the changes as followed：Two dopants solute in crytal both 1.Enlarge the crystal volume due to their larger ion radius than gallium and lanthanum ions’. 2.Suppress the LaGaO3 grain growth. 3.Raise the electrical conductivity. The substitution reaction in the perovskite type of solid solution leads to large defect concentrations and vacancy ordering. And the larger magnesium and strontium ions can also hold additional vacancies in their strain field to help accommodate elastic distortion. Thus oxygen ions migrate in lattice easier, and it causes the resistivity of the ion conductor decrease. Above the solubility, second phase LaSrGaO4 appears on the ground of Sr-doped LaGaO3 bulk, and the conductivity tends to decrease. The great ion radius variation between magnesium and gallium (16%) leads to low solubility of MgO in LaGaO3. Two second phases are observed on the ground of MgO and Ga2O3. As the second phase precipitated, the conductivity changes become unapparent. After aging at 900℃ for long time (50、100、900 hours), all samples’ properties (of crystal structure and conductivity) don’t change apparently. It reflects that the oxygen conductor of doped-LaGaO3 is stable for long-term annealing, and this ceramic material is suitable to be used for electrolyte of solid oxide fuel cell.