  High entropy oxides (HEOs) are a class of materials, containing equimolar
portions of five or more transition metal and/or rare-earth elements. We report
here about the layer-by-layer growth of HEO
[(La$_{0.2}$Pr$_{0.2}$Nd$_{0.2}$Sm$_{0.2}$Eu$_{0.2}$)NiO$_3$] thin films on
NdGaO$_3$ substrates by pulsed laser deposition. The combined characterizations
with in-situ reflection high energy electron diffraction, atomic force
microscopy, and X-ray diffraction affirm the single crystalline nature of the
film with smooth surface morphology. The desired +3 oxidation of Ni has been
confirmed by an element sensitive X-ray absorption spectroscopy measurement.
Temperature dependent electrical transport measurements revealed a first order
metal-insulator transition with the transition temperature very similar to the
undoped NdNiO$_3$. Since both of these systems have a comparable tolerance
factor, this work demonstrates that the electronic behaviors of $A$-site
disordered perovskite-HEOs are primarily controlled by the average tolerance
factor.
