Mettan, X.Jaćimović, J.Barišić, O. S.Pisoni, A.Batistić, I.Horváth, E.Brown, S.Rossi, L.Szirmai, P.Farkas, B.Berger, H.Forró, L.2019-10-152019-10-152019-10-152019-10-1010.1038/s42005-019-0224-7https://infoscience.epfl.ch/handle/20.500.14299/162023Thermal 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.anataseTiO2thermal conductivitythermoelectricitysingle-crystalnanowirenanoengineeringtext::journal::journal article::research article