Given that the Y 2 Ti 2 O 5 S 2 structure would not necessarily be expected to show avoided crossings, it is worth exploring where these features originate from. The atom-projected phonon density of states would normally be used to elucidate which clusters of bands originate from which species. However, as the majority of the avoided crossings are between 6-14 THz, where the PDOS shows overlap between multiple atom types (Figure ), it is not possible to tell the different contributions apart. We therefore instead projected the elemental eigendisplacements, which can be interpreted as the extent to which atoms are displaced along the mode, onto the phonon dispersion (Figure ). This analysis shows which atomic displacements contribute most to the phonon dispersion at each band and wavevector. the biggest frequency gap between them are hard to assign to the movement of a particular atom, so it is likely they are result of a symmetry-forbidden crossing.