Example: effect on of isotopic disorder
- Normal germanium is 37% 74Ge, with the rest consisting of isotopes
with mass 70, 72, 73, and 76
- sample that is isotopically enriched to 94% 74Ge
- the thermal conductivity is increased considerably at low temperatures, causing the temperature dependence of the thermal conductivity for an isotopically enriched crystal to be sharper than that of a crystal with naturally abundant isotopes
- Thus, crystals that are normally isotopically pure have a steeper rise
in 𝜅ℓ at low temperatures than those with several isotopes
