The calculated lattice thermal conductivity κl of both compounds is shown in Figure . The lattice thermal conductivity decreases with temperature increases due to greater phonon-phonon scattering at higher temperatures. The lattice thermal conductivity of both compounds is found to be relatively low as expected, particularly in the inter-layer (z) direction, with Sc2Si2Te6 exhibiting higher lattice thermal conductivity values than Sb2Si2Te6 (by a factor of ~3x). This behaviour can be rationalised through the calculated phonon dispersions, which are provided in Figure respectively, and so these ranges are used in our analysis.