Thermal conductivity of isotopically enriched diamonds

The results of Anthony et al. Phys. Rev. B 42, 1104 (1990) on the thermal conductivity at 25 ^ of diamonds grown with a reduced ^13C concentration are analyzed. The effect of reducing the ^13C concentration is about ten times greater than these authors expected, but it is shown here that the results are not out of line with calculations made by using the variational theory of thermal resistivity, although exact predictions of the effect could not have been made prior to the measurements.