The effect of Pr co-doping on the densification and electrical properties of Sr-LaAlO3

Abstract

Perovskite-type materials have been investigated extensively in the attempt to discover new electrolyte materials for solid oxide fuel cells (SOFC) operating at low temperatures. These materials include LaAlO 3 -based perovskite, which, when adequately doped, presents high ionic conductivity. However, despite the high conductivity of doped LaAlO 3 , two characteristics limit its application as solid electrolyte: low sinterability and p-type electronic conductivity in oxidizing conditions. The purpose of this work was to investigate the effect of Pr co-doping on the densification and electrical conductivity of Sr-doped LaAlO 3 . The addition of Pr eliminated the deficiencies mentioned above. Pr in solid solution acts as a perfect sintering aid because promoted densification without forming secondary phase which should be detrimental for electrical conduction. The addition of Pr also increased the bulk electrical conductivity measured in air atmosphere but had no effect at low oxygen partial pressure. However, the addition of Pr had a strong effect on the grain boundary, improving the ionic grain boundary electrical conductivity at air atmosphere which was attributed to the Pr influence on the space charge layer.

Effects of Sr and Mn co-doping on microstructural evolution and electrical properties of LaAlO3

“…larger atoms scatter more electrons compared to lighter ones and thus create a higher signal, the dark regions correspond to a phase rich in low atomic number elements as compared to the brighter matrix. The brighter grains are richer in La, while the darker grains have a composition closer to that of the theoretical phase, in similar way to other published results [3,15]. It is also interesting to note the differences in grain size and grain size distribution of the different compositions and sintering conditions.…”

“…4), with some grains richer in La as discussed previously. The distribution of Sr is uniform and homogeneous throughout the en-tire sample, as shown by EDS analysis in a previous work [15].…”

Ionic and electronic transport in calcium-substituted LaAlO3 perovskites prepared via mechanochemical route

“…The substitutions of lanthanum by alkaline-earth elements (A = Ca, Sr, Ba) [2˗4, 9,10] or aluminum by magnesium [4,8,10] as well as simultaneous co-substitutions into both sublattices [4,10˗12] Enhancement of the ionic conductivity was also achieved via co-doping by Ba and Y into La and Al sublattices, respectively [1], while the substitution of aluminum by manganese in (La,Sr)AlO3-δ results in an increase of electronic transport [3,14,15]. Villas-Boas and de Souza [16] reported a positive effect of Pr co-doping on the electrical transport properties of Sr-substituted LaAlO3, mainly by suppressing the grain boundary resistivity.…”

Recent Progress in the Design, Characterisation and Application of LaAlO3- and LaGaO3-Based Solid Oxide Fuel Cell Electrolytes

“…The possibility of forming good oxygen-ionic conductivity by doping LaAlO 3 oxides has promoted studies on their potential application in SOFCs [53,65,71,[82][83][84][85][86][87][88][89][90]. The codoping strategy is a beneficial way to further increase ionic conductivity [80,82,83,87]; this is due to the fact that, along with Equation (2), an additional quantity of oxygen vacancies can be formed according to the following mechanism [80]:…”

“…Therefore, co-doped (La,Sr)(Al,Mn)O 3 is attributed to mixed ionic-electronic conductors (MIEC). The Pr-doping of (La,Sr)AlO 3 had a positive influence on transport properties due to the suppression of grain boundary resistivity [85], and the isovalent substitution of La 3+ -ions with Sm 3+ -ions in (La,Sr)AlO 3−δ resulted in the formation of a pronounced mixed ion-electron conduction [88] due to the generation of more electrons than in the case of the aliovalent substitution of La 3+ ions with Ba 2+ ions.…”