Low κ latt is often associated with materials composed of heavy elements with weak chemical bonds, and it is therefore interesting that, given CTO is the lightest of the three materials (c.f. Table ), it also has the lowest κ latt . This indicates that differences in structure and bonding, rather than the mass of the A-site cation, play a significant role in determining the lattice thermal conductivity. To investigate this further, we applied the constant relaxation-time approximation (CRTA) analysis developed in pre- Calculated lattice thermal conductivity of the three perovskites examined in this work at T = 1000 K. Each row gives the three diagonal components of the κ κ κ latt tensors, κ xx , κ yy and κ zz , together with the diagonal average κ ave and its decomposition into harmonic and lifetimes components κ κ κ/τ CRTA ave and τ CRTA as defined in Eq. 3. The atomic masses and radii 75 of the A-site cations are also listed for comparison. vious work to the κ ave . In this model, the κ κ κ latt is written as: