Thermal conductivity of metallic glasses

The thermal diffusivity D of three metallic glasses Fe₈₀B₂₀, Fe₄₀Ni₄₀P₁₄B₆, and Fe₃₂Ni₃₆Cr₁₄P₁₂B₆ has been measured from 160 to 500 K by the laser-flash radiometry method and the thermal conductivity K has been calculated from these data. The accuracy of D and K is 6% and 8%, respectively. The electronic contribution (K_e) to the thermal conductivity, evaluated by using the Wiedemann-Franz law, increases almost linearly with increasing temperature. The phonon thermal conductivity K_ph follows the temperature dependence exhibited by all amorphous dielectrics, i.e., K_ph is roughly proportional to the phonon specific heat, thus giving an approximately constant phonon mean free path. When the metalloid atom B is replaced by P or the number of chemical components in the alloy is increased, both K_e and K_ph decrease, but the drop in K_ph is much more significant. The phonon mean free paths for Fe₈₀B₂₀ and Fe₄₀Ni₄₀P₁₄B₆ are 14 and 12 Å, respectively, which are substantially higher than the values (5-8 Å) for amorphous insulators.