Phonon scattering from the boundaries of small crystals embedded in a dielectric porous-glass matrix

The thermal conductivity of porous glass with randomly distributed connecting pores ∼70 Å in size (glass porosity ∼25%), as well as of a porous glass + NaCl composite, was measured in the temperature range 5–300 K. NaCl filled one fourth of the pores in the composite. The experimental results on the composite thermal conductivity can be accounted for only by assuming that phonons scatter from the boundaries of NaCl nanocrystals embedded in channels of the porous glass.