| 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.La1-xNaxGa0.84Mg0.16O3-?,La1-xNaxGa O3-?,La1-xLi1-xGa O3-?,La1-xKxGa0.84Mg0.16O3-?and 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 La0.94Na0.04Ga0.84Mg0.16O3-?possesses 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 La0.98K0.02Ga0.84Mg0.16O3-?is 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.La1-xNdxGa0.9Mg0.1O3-?samples were synthesized to study the effect of the A site ion radius on electrical properties.As a result,the conductivity of La1-xNdxGa0.9Mg0.1O3-?decreases 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 La0.8Sr0.2Ga0.83Mg0.17O3-?to investigate the electrical properties.Sample La0.8Sr0.17Pb0.03Ga0.83Mg0.17O3-?crystallizes 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. |
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