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X-Ray Nanodiffraction Studies of Ionically Controlled Nanoscale Phase Separation in Cobaltites



Geoffery Rippy, Lacey Trinh, Alexander M. Kane, Aleksey L. Ionin, Michael S. Lee, Rajesh V. Chopdekar, Joyce M. Christiansen-Salameh, Dustin A. Gilbert, Alexander Grutter, Peyton D. Murray, Martin V. Holt, Zhonghou Cai, Kai Liu, Yayoi Takamura, Roopali Kukreja


Complex oxide heterostructures provide access to emergent functional and structural phases which are not present in the bulk constituent materials. In this letter, we focus on Gd/La0.67Sr0.33CoO3 (LSCO) heterostructures due to the high oxygen ion conductivity, as well as the coupled magnetic and electronic properties of LSCO, which are strongly dependent on the oxygen stoichiometry. This combination of properties enable the ionic control of the functional properties of LSCO thin films through the presence of oxygen getter layers such as Gd. We utilize x-ray nanodiffraction to directly image the nanoscale morphology of LSCO thin films as they are progressively transformed from the equilibrium perovskite phase to the metastable brownmillerite (BM) phase with increasing Gd thickness. Our studies show the coexistence of perovskite and BM phases with a critical oxygen vacancy concentration threshold which leads to the formation of extended BM filaments. These filaments were oriented at either 10° or 50-60° angles from the [100] direction. In addition to lateral phase separation, we observed phase separation within the film thickness possibly due to pinning of the perovskite or BM phase by the substrate/LSCO or Gd/LSCO interface, respectively. Furthermore, strain maps reveal that the perovskite phase changes from compressive to tensile strain on opposite sides of a BM filament.
Physical Review Materials


Diffraction, oxide, ionics, thin film, perovskite, brownmillerite, phase separation


Rippy, G. , Trinh, L. , Kane, A. , Ionin, A. , Lee, M. , Chopdekar, R. , Christiansen-Salameh, J. , Gilbert, D. , Grutter, A. , Murray, P. , Holt, M. , Cai, Z. , Liu, K. , Takamura, Y. and Kukreja, R. (2019), X-Ray Nanodiffraction Studies of Ionically Controlled Nanoscale Phase Separation in Cobaltites, Physical Review Materials, [online], (Accessed April 19, 2024)
Created August 4, 2019, Updated October 12, 2021