【作者】 刘欣然；

【导师】 刘志国；

【作者基本信息】 哈尔滨工业大学 ， 凝聚态物理， 2021， 硕士

【摘要】 LaGaO₃基材料作为固体氧化物燃料电池电解质具有广泛的研究和应用背景,自20世纪90年代以来发展迅速。Sr²⁺和Mg²⁺是被广泛使用的掺杂离子,掺杂这两种离子可以为LaGaO₃材料提供氧空位,增加氧离子传输通道,提高材料导电性。在掺杂20%Sr、17%Mg时,电导率最高,但在继续增加掺杂量的情况下,容易产生Sr La Ga₃O₇等杂相。由于碱金属离子为+1价,在相同掺杂量下可以提供更多氧空位,因此本文尝试在LaGaO₃中A位掺杂碱金属离子（Li⁺/Na⁺/K⁺）观察其导电性的变化;同时,在LaGaO₃材料中B位掺杂Mg以提高A位离子的固溶度,研究碱金属/Mg双掺杂对电解质性能的影响。采用固相法制备了La_1-xNa_xGa_0.84Mg_0.16O_3-δ、La_1-xNa_xGa O_3-δ、La_1-xLi_1-xGa O_3-δ、La_1-xK_xGa_0.84Mg_0.16O_3-δ等样品,并通过X射线衍射实验观察成相情况。以上几种碱金属掺杂样品成相良好,均无杂相生成,样品中元素分布较均匀,且致密度较高。交流阻抗结果显示,Na掺杂样品中La_0.94Na_0.04Ga_0.84Mg_0.16O_3-δ的电导率较高,800℃条件下电导率0.093 S/cm,活化能为0.35 e V。K掺杂样品中La_0.98K_0.02Ga_0.84Mg_0.16O_3-δ的电导率最高,800℃达到0.085 S/cm。与LaGaO₃类似,NdGaO₃也具有正交钙钛矿结构,Nd³⁺半径略小于La³⁺且La³⁺可以与Nd³⁺在A位以任意比例替代。本文制备了La_1-xNd_xGa_0.9Mg_0.1O_3-δ,研究A位离子半径对钙钛矿结构镓酸盐电解质导电性能的影响。实验结果表明,Nd³⁺替代La³⁺使钙钛矿材料电导率下降,说明在形成钙钛矿结构的情况下,A位离子半径越大,氧离子在材料中迁移越容易。由于Pb²⁺能提供孤对电子,可以降低氧离子迁移时的势垒,因此在La_0.8Sr_0.2Ga_0.83Mg_0.17O_3-δ中用Pb取代Sr,研究了其导电性质。样品La_0.8Sr_0.17Pb_0.03Ga_0.83Mg_0.17O_3-δ成相及电导率较好,800℃条件下电导率为0.147S/cm,活化能为0.45 e V,性能较不掺杂Pb时性能有所提升;在Pb掺杂量超过6%时,样品中产生杂相,且逐渐偏离立方结构,电导率有所降低。更多还原

【Abstract】 As electrolytes for solid oxide fuel cells,LaGaO₃-based materials exhibit extensive background for investigation and application,and have been developed rapidly since the 1990s.Sr and Mg are widely used as doping ions to create oxygen vacancies in LaGaO₃ materials,enlarge oxygen ion transport channels and improve the conductivity.When doping 20%Sr and 17%Mg,the highest conductivity is attained,while impurity such as Sr La Ga₃O₇ appears with further doping.Due to the valence of+1,alkali metal doping can provide more oxygen vacancies than alkaline-earth metal at the same doping level.Therefore,alkali metal（Li⁺/Na⁺/K⁺）doping was attempted at the A sites of LaGaO₃,and the electrical propterties were investigated.Mg co-doping was performed at the B site of LaGaO₃ materials to increase the doping limit at A sites,and the effect on electrical properties was evaluated.La_1-xNa_xGa_0.84Mg_0.16O_3-δ,La_1-xNa_xGa O_3-δ,La_1-xLi_1-xGa O_3-δ,La_1-xK_xGa_0.84Mg_0.16O_3-δand other samples were prepared by solid state technique,and the phase composition was checked by X-ray diffraction.Perovskite phase with high density was formed for the above-mentioned samples,and no impurity was detected.Furthermore,the distribution of elements in the sample is uniform.The AC impedance spectra show that sample La_0.94Na_0.04Ga_0.84Mg_0.16O_3-δpossesses the highest conductivity of 0.093 S/cm at800℃,with the activation energy 0.35 e V.Among the K doping samples,The conductivity of La_0.98K_0.02Ga_0.84Mg_0.16O_3-δis the highest,i.e.,0.085 S/cm at 800°C.Similar to LaGaO₃,NdGaO₃ also crystallizes in perovskite structure with orthorhombic symmetry.The radius of Nd³⁺is slightly smaller than that of La³⁺,and La can be substituted by Nd at any ratio.La_1-xNd_xGa_0.9Mg_0.1O_3-δsamples were synthesized to study the effect of the A site ion radius on electrical properties.As a result,the conductivity of La_1-xNd_xGa_0.9Mg_0.1O_3-δdecreases with increasing Nd content,indicating that the higher average radius at A sites,the easier the migration of oxygen ion in these materials.Pb can provide a lone pair of electrons,which can reduce the barrier for oxygen ion migration,hence Pb was doped for Sr in La_0.8Sr_0.2Ga_0.83Mg_0.17O_3-δto investigate the electrical properties.Sample La_0.8Sr_0.17Pb_0.03Ga_0.83Mg_0.17O_3-δcrystallizes well,and exhibits a high conductivity of 0.147 S/cm at 800℃,and an activation energy of0.45e V,exhibiting better performance than the samples without Pb doping.When the doping level of Pb exceeds 6%,impurity phase is detected,and the symmetry deviates from cubic.Consequently,the conductivity decreases as well.更多还原