A Comprehensive Multimodal Study of La0.45Sr0.45TiO3 Structure as Matrix for the Exsolution Process: From the Average to the Local Scale.

Abstract

We report a comprehensive structural investigation of La0.45Sr0.45TiO3 (LSTO) as a ceramic matrix for exsolution-based fuel electrodes in solid oxide fuel cells and electrolyzers. Synchrotron radiation powder diffraction reveals an average cubic perovskite structure from room temperature to 900°C, even under the reducing exsolution conditions (5% H2/Ar), where Ti ions occupy centrosymmetric sites. However, pre-edge features of X-ray Absorption Spectroscopy spectra at the Ti K-edge indicate Ti off-centering. Combined Pair Distribution Function analysis of synchrotron and neutron diffraction uncovers local distortion on the 2-3 nm scale. An a-a-c+ octahedral-tilting, coupled with Sr/La ordering in alternating planes perpendicular to the c axis, reduces the local symmetry to the orthorhombic P21am space group. Ti ions shift away from La3+-rich planes, exerting stronger electrostatic repulsion than Sr2+-rich ones, while oxygen ions are drawn toward them. This asymmetric environment creates the observed Ti off-centering. Local distortions persist up to 900°C under a reducing atmosphere. Density Functional Theory calculations support this structural model and clarify the material's electronic structure. The highest occupied electronic states are primarily Ti-derived, consistent with Ti reduction observed by XPS. Excess charge preferentially localizes on two of four Ti ions per orthorhombic cell, exhibiting weak ferromagnetic coupling.