Directional heat dissipation across the interface in anatase-rutile nanocomposites

Understanding the structures and properties of interfaces in (nano-)composites helps to reveal their important influence on reactivity and overall performance. TiO₂ is a technologically important material, and anatase/rutile TiO₂ composites have been shown to display enhanced photocatalytic performance over pure anatase or rutile TiO₂. This has been attributed to a synergistic effect between the two phases, but the origin of this effect as well as the structure of the interface has not been established. Using Raman spectroscopy, here we provide evidence of distinct differences in the thermal properties of the anatase and rutile moieties in the composite, with anatase becoming effectively much warmer than the rutile phase under laser irradiation. With the help of first-principles calculations, we analyze the atomic structure and unique electronic properties of the composite and infer possible reasons for the directional heat dissipation across the interface.