Our calculations predict a κ latt ordering of Bi 2 SO 2 ≈ Bi 2 SeO 2 > Bi 2 TeO 2 . The predicted κ latt at T = 800 K are larger than the equivalent Bi 2 Ch 3 , and the κ latt of Bi 2 SeO 2 is higher than that of both the lower-symmetry P nma and higher-symmetry R3m phases of Bi 2 Se 3 . The κ latt of Bi 2 SO 2 and Bi 2 SeO 2 are also larger than those of SnS and SnSe. Partial substitution of the chalcogen with oxygen therefore results in a larger κ latt compared to similar chalcogenides. On the other hand, all three Bi 2 ChO 2 are predicted to have significantly lower κ latt than the oxide perovskite SrTiO 3 , indicating the oxychalcogenides partially retain the favourable low lattice thermal conductivity associated with the chalcogenides. This may be due in part to the layered structure.