  Designing and understanding functional electronic and magnetic properties in
perovskite oxides requires controlling and tuning the underlying crystal
lattice. Here we report the structure, including oxygen and cation positions,
of a single-crystal, entropy stabilized perovskite oxide film of
La(Cr0.2Mn0.2Fe0.2Co0.2Ni0.2)O3 grown on SrTiO3 (001). The parent materials
range from orthorhombic (LaCrO3, LaMnO3 and LaFeO3) to rhombohedral (LaCoO3 and
LaNiO3), and first principles calculations indicate that these structural
motifs are nearly degenerate in energy and should be highly distorted
site-to-site. Despite this extraordinary local configurational disorder on the
B-site sublattice, we find a structure with unexpected macroscopic crystalline
homogeneity with a clear orthorhombic unit cell, whose orientation is
demonstrated to be controlled by the strain and crystal structure of the
substrate for films grown on (La0.3Sr0.7)(Al0.65Ta0.35)O3 (LSAT) and NdGaO3
(110). Furthermore, quantification of the atom positions within the unit cell
reveal that the orthorhombic distortions are small, close to LaCrO3, which may
be driven by a combination of disorder averaging and the average ionic radii.
This is the first step towards understanding the rules for designing new
crystal motifs and tuning functional properties through controlled
configurational complexity.
