Phase stability. As configurational entropy favors single-phase solid solution, the presence of many elements may stabilize phases even if the compositional end members are strongly metastable, like e.g. TbMnO3 and GdMnO3. The high entropy compositions used for this study enable incorporation of large R 3+ in the hexagonal manganite structure. As all nanocrystalline samples and the two bulk HEO2-b and HEO5-b samples show high phase purity, with only trace amounts of the orthorhombic phase found for HEO2-n, HEO3-n and HEO5-n, the differences in composition within the present study (Table ) does not significantly affect the phase stability. This indicates that the high configurational entropy is imperative for stabilizing the hexagonal structure even for tolerance factors as high as t = 0.865, which is higher than the "limit" of t = 0.855 usually reported for these materials. The HEO1-b sample was not phase pure, even though it has the lowest tolerance factor of all samples studied (Table ). This tolerance factor is determined by the size of the size of the cations in the material and was calculated by assuming the oxidation states of R and Mn to be R 3+ and Mn 3+ . As the oxidation states of Mn and Tb depend on both temperature and atmosphere, this assumption is imprecise. In reducing conditions or at higher temperatures, Ti 4+ can cause reduction of Mn to Mn 2+ instead of being change compensated by excess Oi, which lowers the tolerance factor. It is therefore likely that the 'effective' tolerance factor of Ti-doped samples is lower at the synthesis temperature (1450 °C for bulk samples) than that of undoped samples, which promotes formation of the hexagonal phase. For Tb, the opposite effect occurs; at higher temperatures, less Tb 4+ will be present, and the larger size of Tb 3+ (0.98 Å) compared to that of Tb 4+ (0.82 Å) will then increase the tolerance factor, promoting formation of the orthorhombic perovskite phase. As the HEO1-b sample needs to be synthesized at higher temperatures through the solid-state synthesis method, and contains Tb but no Ti, the 'effective' tolerance factor is likely too high to achieve phase pure hexagonal manganite.