Pr0.5Ca0.5CoO3 presents in bulk form a singular valence, spin-state and metal-insulator transition. We report a reduction of the structural symmetry from Pnma (bulk) to P212121 (film) revealed by synchrotron X-rays. In contrast to the general tendency reported for strained ferromagnetic Co perovskite films, we show that unexpectedly a nominal tensile strain can also be compatible with the presence of alternating O vacancy planes parallel to the interface.

Double-cell superstructure and vacancy ordering in tensile-strained metallic thin films of Pr0.50Ca0.50CoO3 on LaAlO3
Jessica Padilla-Pantoja, Xavier Torrelles, Jaume Gazquez, Juan Rubio-Zuazo, Javier Blasco, Javier Herrero-Martín, Jose Luis García-Muñoz
Physical Review Materials 3, 104407, 9pp, 2019
DOI: 10.1103/PhysRevMaterials.3.104407

Figure: (top) Selected synchrotron X-ray diffraction scans at RT from PCCO thin film, showing a double-cell in the film due to the (1/2, 1/2, 1/2) superstructure. (H,K,L) reflections are expressed in the LAO basis. (bottom) High-resolution Z-contrast image of the PCCO/LAO interface. d1 and d2 signal different (Pr/Ca) - (Pr/Ca) distances. Yellow circles in the image Fourier transform mark two superlattice peaks. The arrows mark the O-deficient planes. Scale bar 10 nm. Histogram of the out-of-plane distance values (Δz) between lanthanide neighbors in successive layers.

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