Interestingly, all nanocrystalline materials are highly insensitive to the cooling rates investigated, which are limited up to 20 °C/min by the instrument. This implies very fast oxidation kinetics compared to literature reports. The samples containing both Ti and Tb (Figure (b)-(d)) show the highest oxygen storage capacities, as expected from previous studies of Tia and Tb in hexagonal manganites. The oxygen content of these samples is also above the δ = 0.33 limit for oxidation of 2/3 of Mn only, giving 2 oxygen interstitials per 30-atom unit cell. Oxidation of Tb 3+ to Tb 4+ can charge compensate more oxygen interstitials than possible in samples with only 'inert' R cations. Ti-doped samples (Figure (b)-(e)) show significant oxygen content at T > 350 °C, as Ti increases the thermal stability of interstitial oxygen, and a stable plateau is not reached at T > 700 °C where all Mn is presumed to be Mn 3+ , indicating a small underestimation in the assumption of δ for these samples.