Large thermal conductivity switch ratio in ferroelectric materials under electric field through first-principles calculation

Barium titanate is considered as an example that has order-disorder feature due to the existence of the “central mode”, which could be a potential material that can have large thermal conductivity switch ratio if the disordered structure can be aligned to the ordered structure. Solving the Boltzmann transport equation (ShengBTE), the fully disordered structure was found to have a thermal conductivity a factor of ~4 lower than the ordered structure. Then an electric field was applied in the simulations to align the disordered structure. In doing so, the polarization hysteresis loop of barium titanate in rhombohedral phase is obtained for the first time by a full first-principles method. We found the electric field can at most increase the thermal conductivity of ordered structure by a factor of ~2. Therefore, combining both of the above effects suggests a maximum possible switch ratio of ~8. These results yield two guidelines for searching high thermal conductivity switch ratio in ferroelectric materials: the structure should be single domain, and the phase transition should be fully order-disorder rather than displacive.