Disordered solids form when atomic size difference is small and Δ Δ G m i x is not negative enough. This is because every atom is about the same size and can easily substitute for each other and Δ Δ H m i x is not low enough to form a compound. More-ordered HEAs form as the size difference between the elements gets larger and Δ Δ G m i x gets more negative. When the size difference of each individual element become too large, bulk metallic glasses form instead of HEAs. High temperature and high Δ Δ S m i x also promote the formation of HEA because they significantly lower Δ Δ G m i x , making the HEA easier to form because it is more stable than other phases such as intermetallics.