Ordering up the Minimum Thermal Conductivity of Solids

Disorder usually interferes with heat conduction in most materials, but an exception has been found for insulators made from multiple layers of crystalline tungsten selenide.  Although record-high thermal conductivities in ordered materials such as diamond and carbon nanotubes have captured headlines, a few researchers have pursued materials with the minimum thermal conductivity. Although the best thermal insulators are porous (like styrofoam), many applications require electrical and mechanical properties that are only available in fully dense materials. The best nonporous insulators are amorphous dielectrics, which have conductivities as much as four orders of magnitude less than that of diamond.  Now, researchers are making progress on achieving substantially lower thermal conductivities through the introduction of material order.