The HEO1-n and HEO2-n samples oxidize fast (Figure ) and the lattice parameters stabilize within 20 minutes or less at all temperatures, with shorter times at higher temperatures. Ti-doped HEO2-n is subtly faster than the undoped HEO1-n, as expected from previous studies of Ti 4+ -doping. As some R3c is present before switching gas from N2 to O2 (Figure ), the time necessary for full oxidation from a completely unoxidized state is believed to be longer, but only subtly as the rate of oxidation is expected to fastest for the lowest degree of oxidation. The oxidation time for HEO1-n is substantially shorter than previous findings for RMnO3 without aliovalent dopants, with e.g. Y0.95Pr0.05MnO3 reported to need several hours to oxidize in air at multiple temperatures and HoMnO3 being far from fully oxidized after 20 minutes at 250 °C in O2 atmosphere. This shows that high entropy compositions greatly improves the oxidation rate of hexagonal manganites. This may be attributed to lattice site disorder causing overlap in site energies which promotes ionic transport. Site disorder has e.g. been shown to enhance Li + transport in solid electrolytes, and similar microscopic mechanisms may also be relevant for other 2D and 3D ionic conductors with high configurational entropy.