High-temperature thermal conductivity of electron-irradiated diamond

The damage in diamond produced by electrons of 0.60, 0.90, and 1.50 MeV was found to give a reduction of the thermal conductivity between 320 and 450 K. The damage was stable upon annealing to about 800 K. For type-IIa diamond the radiation-induced thermal resistivity $R\left(T\right)\mathrm{}$ equals $2.4\times {10}^{-21\mathrm{}}{n}_V$ ${\mathrm{W}}^{-1\mathrm{}}$ cm K at 320 K and $1.7\times {10}^{-21\mathrm{}}{n}_V$ ${\mathrm{W}}^{-1\mathrm{}}$ cm K at 450 K, where $n_V$ denotes vacancy concentration. This conclusion was reached by taking the displacement energy of carbon atoms to be 80 eV, by assuming no instantaneous recombination, and by neglecting any effect of displaced atoms on the high-temperature thermal conductivity. For type-I diamond, larger values were found for $R\left(T\right)\mathrm{}$, suggesting that displaced carbon atoms might be trapped on the nitrogen impurity. The results for irradiated type-IIa diamond and unirradiated type-I diamond indicate that vacancies cause somewhat more strain in the lattice than nitrogen. For these two kinds of point defects there was also a difference in the temperature dependence of the thermal conductivity.