On the other hand, the τ CRTA do not display any clear trends (Fig. , Table ). Pnma SnSe, GeTe and SnTe have averaged lifetimes of 3.89-3.98 ps at 300 K, while the τ CRTA of the lighter Pnma GeSe is ∼50% longer at 6.03 ps. Fm 3m GeSe and GeTe have much shorter averaged lifetimes of ∼ 0.5 ps, respectively, whereas SnTe has a much longer τ CRTA = 4.67 ps that exceeds three of the four Pnma systems. The two R3m structures both have longer τ CRTA than other phases with the same composition. Finally, Cmcm SnSe has a τ CRTA around 75% smaller than Pnma SnSe, which compensates for the ∼3 × larger κ κ κ/τ CRTA iso to yield an overall lower κ iso . The trends in the τ CRTA among the chalcogenides are thus complex, requiring a more detailed analysis of the underlying physics, which is the subject of the following section.