The group velocities were previously discussed in the context of the phonon dispersion in Section 3. as a function of frequency. The lifetimes are calculated at T = 1000 K. The modal contributions to the lattice thermal conductivity κ λ at 1000 K are overlaid as a colour scale so that the darker the colour the greater the contribution of the mode to the lattice thermal conductivity. Plotted with ThermoPlotter. The phonon lifetimes are inversely proportional to the phonon linewidths Γ λ via: