%AAryana, Kiumars%AStewart, Derek%AGaskins, John%ANag, Joyeeta%ARead, John%AOlson, David%AGrobis, Michael%AHopkins, Patrick%BJournal Name: Nature Communications; Journal Volume: 12; Journal Issue: 1 %D2021%I %JJournal Name: Nature Communications; Journal Volume: 12; Journal Issue: 1 %K %MOSTI ID: 10316669 %PMedium: X %TTuning network topology and vibrational mode localization to achieve ultralow thermal conductivity in amorphous chalcogenides %XAbstract Amorphous chalcogenide alloys are key materials for data storage and energy scavenging applications due to their large non-linearities in optical and electrical properties as well as low vibrational thermal conductivities. Here, we report on a mechanism to suppress the thermal transport in a representative amorphous chalcogenide system, silicon telluride (SiTe), by nearly an order of magnitude via systematically tailoring the cross-linking network among the atoms. As such, we experimentally demonstrate that in fully dense amorphous SiTe the thermal conductivity can be reduced to as low as 0.10 ± 0.01 W m −1 K −1 for high tellurium content with a density nearly twice that of amorphous silicon. Using ab-initio simulations integrated with lattice dynamics, we attribute the ultralow thermal conductivity of SiTe to the suppressed contribution of extended modes of vibration, namely propagons and diffusons. This leads to a large shift in the mobility edge - a factor of five - towards lower frequency and localization of nearly 42% of the modes. This localization is the result of reductions in coordination number and a transition from over-constrained to under-constrained atomic network. %0Journal Article