Overall, the P span two orders of magnitude and are largest for the more symmetric structures, whereas the Ñ2 span one order of magnitude and are largest for the less symmetric structures. Together, these two competing factors account for the roughly one order of magnitude variation in the τ CRTA between 0.48 for Fm 3m GeSe and and 6.07 ps for R3m SnTe. The long τ CRTA of Fm 3m SnTe and the two R3m phases highlighted in the previous section can, based on the analysis here, be attributed to a combination of relatively low P and Ñ2 , indicative of weak anharmonicity and a small scattering phase space, respectively. Similarly, as noted above, the analysis shows that the weak anharonicity (low P) of the Pnma phases is compensated by a large number of scattering pathways (large Ñ2 ) due to the large primitive cells and relatively complex phonon spectra, and this is why these four systems do not follow the trend in Fig. . Finally, the ∼80% shorter averaged lifetime of Cmcm SnSe compared to the related Pnma phase is a favourable balance of an order of magnitude higher P but a 50% smaller Ñ2 .