where the terms are defined as in Eq. 3 above. As for 𝜿 latt the 𝜿 𝜏 CRTA ⁄ are tensors, and the 𝜏 CRTA may be taken as a scalar, like the 𝜏 𝜆 , or as a tensor to provide some flexibility to account for anisotropy in the averaged mode lifetimes. phases the lifetimes increase by a factor of two from Bi2S3 to Bi2Se3, but are reduced by ~25 % in Bi2Te3 compared to Bi2Se3. An increase in lifetime counteracting a reduced harmonic term was also observed when comparing the thermal conductivity of SnS and SnSe. This method of analyzing the 𝜿 latt and comparing between materials is relatively new, but we have previously performed similar calculations on SnS/SnSe and CoSb3, all of which are widely-studied thermoelectric materials. For SnSe, we calculated a room-temperature 𝜅 ave of 1.58 W m -1 K -1 together with a 𝜅 𝜏 CRTA ⁄ of 0.372 W m -1 K -1 ps -1 and a 𝜏 CRTA of 4.23 ps. The 𝜅 ave falls between the Pnma and R3 ̅ m phases of Bi2Se3. The harmonic term is larger than in both materials, and the higher 𝜅 ave of R3 ̅ m Bi2Se3 is thus due to its longer average lifetimes while the lower thermal conductivity of Pnma Bi2Se3 is due to both the smaller harmonic term and shorter 𝜏 CRTA . For CoSb3, we obtained 𝜅 ave = 9.98 W m -1 K -1 with 𝜅 𝜏 CRTA ⁄ = 0.273 W m -1 K -1 ps -1 and 𝜏 CRTA = 36.6 ps. The harmonic term is smaller than in both sulfides, comparable to the R3 ̅ m phase of Bi2Se3, and larger than both tellurides. However, the lifetime is much larger than all six chalcogenide materials investigated here, by a factor of 6-17 ×, and this is the main reason for its much larger thermal conductivity.