Glass-oxide nanocomposites as effective thermal insulation materials

With extremely disordered atomic structures, a glass possesses a thermal conductivity k that approaches the theoretical minimum of its composition, known as the Einstein's limit.¹ Depending on the material composition and the extent of disorder, the thermal conductivity of some glasses can be down to 0.1-0.3 W/m·K at room temperature,^2,3 representing some of the lowest k values among existing solids. Such a low k can be further reduced by the interfacial phonon scattering within a nanocomposite that can be used for thermal insulation applications. In this work, nanocomposites hot pressed from the mixture of glass nanopowder (GeSe₄ or Ge₂₀Te₇₀Se₁₀) and commercial SiO₂ nanoparticles, or pure glass nanopowder, are investigated for the potential k reduction. It is found that adding SiO₂ nanoparticles will instead increase k if the measured k values for usually porous nanocomposites are converted into those for the corresponding solid (k Solid) with Eucken's formula. In contrast, pure glass nano-samples always show k Solid data significantly reduced from that for the starting glass. For a pure GeSe4 nano-sample, k Solid would beat the Einstein's limit for its composition.