Lower limit to the thermal conductivity of disordered crystals

Measurements of the thermal conductivity above 30 K of mixed crystals with controlled disorder, (KBr)1-x(KCN)x, (NaCl)1-x, (NaCn)x Zr1-xYxO2-x/2, and Ba1-xLaxF2+x, support the idea of a lower limit to the thermal conductivity of disordered solids. In each case, as x is increased, the data approach the calculated minimum conductivity based on a model originally due to Einstein. These measurements support the claim that the lattice vibrations of these disordered crystals are essentially the same as those of an amorphous solid.