Anomalous thermal response of bulk diamond to uniaxial (100) strain: A first-principles prediction

Diamond, a material that exhibits ultrahigh thermal conductivity with a sensitive thermal response to stress, is an ideal heat-sink material in the embedded cooling paradigm. This study uses first-principles calculations with the phonon Boltzmann transport equation to predict the variation rules of the thermal conductivity of diamond along the $\langle 100\rangle$ crystal direction under strains at three orders of magnitude: 0.1%, 1%, and 10.5%. Density functional theory is used to predict the stress–strain dependence of diamond and the temperature-dependent thermal conductivity of unstrained diamond. The predictions are in good agreement with the experimental results. The calculated uniaxial strain–thermal conductivity dependence results reveal that the thermal conductivity of diamond abnormally increases by approximately 15% under small-scale uniaxial strain because of the weakened anharmonic interatomic force constants. Under large-scale strain, the thermal conductivity considerably decreases because of reduced phonon group velocities and increased numbers of phonon scattering channels. The findings in this study will guide analyses of the dependence of thermal conductivity on strain in other diamondlike structures, such as Group IV element-based materials. The abnormal thermal response at small strain is expected to lead to the realization of an artificial thermal conduction channel.

Figure 1

Stress-strain relationships in diamond. (a) Isotropic strain and (b) uniaxial strain along the $\langle 100\rangle$ crystal direction.

Figure 2

Grid independence verification.

Figure 3

Calculated phonon dispersion relationships in diamond under different tensile stresses and phonon densities of state (DOSs). (SS strain represents small-scale strain, $\varepsilon =0.1\%$; MS strain represents medium-scale strain, $\varepsilon =1.0\%$; LS strain represents large-scale strain, $\varepsilon =10.5\%$).

Figure 4

(a) Temperature dependence of the thermal conductivity (κ) of diamond. The inset shows the strain dependence of κ (at room temperature, 300 K) under uniaxial and isotropic strains. (b) Mean mode κ under different tensile stresses, (c) contribution to κ from each acoustic band, and (d) normalized cumulative thermal conductivity ${\kappa }_{\mathrm{acc}}/{\kappa }_0$ of isotopically pure diamond.

Figure 5

Strain dependences of (a) squared group velocity, (b) phonon mean free path (The inset shows the corresponding polynomial fitted curves), and (c) phonon lifetime (The inset presents the effects of SS strain on N and U scattering).

Figure 6

Weighted phase space at room temperature as a function of frequency for strained and unstrained diamond.