Designing Optimal Perovskite Structure for High Ionic Conduction

There has been an incomplete understanding of the structure-property relationships that would enable the rational design of better ion-conducting electrolytes for SOFC. Here, using epitaxial thin-film growth, synchrotron X-ray diffraction, impedance spectroscopy, and density-functional theory, we delineate the impact of structural parameters (i.e., unit-cell volume and octahedral rotations) on ionic conductivity in La0_.9Sr0_.1Ga0_.95Mg0_.05O3_-δ. As compared to the zero-strain state, compressive strain reduces the unit-cell volume while maintaining large octahedral rotations, resulting in a strong reduction of ionic conductivity, while tensile strain increases the unit-cell volume while quenching octahedral rotations, resulting in a negligible effect on the ionic conductivity. Calculations reveal that larger unit-cell volumes and octahedral rotations decrease migration barriers and create low-energy migration pathways, respectively. The desired combination of large unit-cell volume and octahedral rotations is normally contraindicated, but through the creation of superlattice structures we experimentally realize both expanded unit-cell volume and strong octahedral rotations which result in an enhancement of the ionic conductivity by 250 % at around 600°C.

NSF Grant OISE-1545907.