Conducting phonon frequencies higher than

In diamond, thermal conductivity occurs by aflow of phonons (see Ch. 11, Sec. 5.2). These phonons are scattered by imperfections such as isotopic imperfections and the scattering varies as the fourth power of the phonon frequency. Thus, the exclusion of C should result in a significant increase in thermal conductivity. This increase was confirmed experimentally as C diamond is reported to have a 50% higher thermal conductivity than natural diamond.i l i It is also reported to be harder than natural diamond by a few percent as determined by the relation between hardness and the elastic coefficients (see Ch. 11, Sec. 10.2). 

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