Tailoring thermal conduction in anatase TiO2

Thermal conductivity (κ) plays an essential role in functional devices. It is advantageous to design materials where one can tune κ in a wide range according to its function: single-crystals and nanowires of anatase polymorph of titanium dioxide, broadly used in applications ranging from photovoltaics, reflective coatings to memristors, have been synthesized in large quantities. Here we identify a new, strong diffusion mechanism of heat by polaronic structures due to oxygen vacancies, which considerably influences both the absolute value and the temperature dependence of κ. The additional decrease of κ is achieved in anatase nanowires organized into foam, where porosity and the quasi-one-dimensional size-effect dramatically hinder the propagation of heat, resulting in an extremely low κ = 0.014 W/Km at room-temperature. Doping this anatase foam could herald promising applications, in particular in thermoelectricity. The thermal properties of a material often determine its suitability for application and use in devices. Here, the thermal conductivity of anatase TiO2 is tuned over three orders of magnitude from bulk crystals to foam samples, by controlling polaronic effects and texturing.