2019 Volume 87 Issue 5 Pages 265-269
In this work, we investigated electrical conduction properties, crystal structures, and electron-density distributions of LaBaGaO4-based protonic conductors; i.e., La0.95M0.05BaGaO4−δ (M = Ba, Sr, and Ca) and La0.9Ba1.1Ga0.9M′0.1O4−δ (M′ = Ga, Al, and In). It was demonstrated from the conductivity measurements that the Sr-substituted sample showed the highest conductivity among La0.95M0.05BaGaO4−δ and the partial substitutions of Al and In for Ga deteriorated the conductivity. To clarify effects of the substitutions on crystal structures and electron-density distributions, we performed a Rietveld refinement and a maximum-entropy method. As a result, it was found that a distortion of the crystal structure was the lowest in the Sr-substituted sample among La0.95M0.05BaGaO4−δ and became larger by the partial substitution for Ga. It was also suggested that both the Al and In substitutions made (Ga, M′)-O bond stronger and thus (Ga, M′)O4 tetrahedra rigid. Such structural changes by the partial substitutions could be considered to affect the electrical conduction properties.