It is typically assumed that acoustic deformation potential scattering limits carrier mobility in thermoelectric materials. However, our detailed charge transport calculations reveal that both electron and hole mobility in Y 2 Te 3 is limited by polar optical phonon scattering (Figures and). In fact, recent studies have revealed that carrier mobility in common semiconductors such as GaAs, CsPbBr 3 , and SnSe 54 is limited by polar optical phonon scattering as well.