Influence of hydration on the thermal transport properties of yttria-doped barium zirconate

Perovskites exhibit excellent protonic conductivity in the mid-temperature range, and among them, yttria-doped barium zirconate (BZY) is considered one of the most promising perovskite proton conductors. Molecular simulations provide an efficient approach to investigating the thermal transport behavior of nanocrystalline materials. The effect of doping concentration on the thermal transport properties of BZY structures was investigated using the equilibrium molecular dynamics (EMD) method combined with phonon spectral energy density (SED) analysis. The results show that the thermal transport properties gradually decrease with increasing doping concentration, and for structures with dopants only and without oxygen vacancies, the thermal conductivity exhibits a similar decreasing trend but remains higher than that of structures containing both dopants and oxygen vacancies. Comparison of phonon lifetime and group velocity reveals that oxygen vacancy defects enhance phonon scattering, thereby leading to a reduction in thermal transport properties, while doping reduces the thermal transport properties by weakening lattice harmonicity. The effect of different hydration levels on the thermal transport properties of BZY was also investigated, and the results indicate that the thermal conductivity fluctuates in structures with low hydration levels and continues to decrease as the proton defect concentration increases with hydration. Further analysis of phonon lifetime and group velocity demonstrates that proton defects reduce the thermal transport properties through both enhanced phonon diffusion and weakened harmonicity.