Thermal conductivity of diamond under extreme pressure: A first-principles study

Abstract

Using a first principles approach based on density functional perturbation theory and an exact numerical solution to the phonon Boltzmann equation, we show that application of large compressive hydrostatic pressure dramatically increases the thermal conductivity of diamond.We connect this enhancement to the overall increased frequency scale with pressure, which makes acoustic velocities larger and reduces phonon-phonon scattering rates. Of particular importance is the often neglected fact that heat-carrying acoustic phonons are coupled through lattice anharmonicity to higher frequency optic modes. An increase in optic mode frequencies with pressure weakens this coupling and contributes to driving the diamond thermal conductivities to far larger values than in any material at ambient pressure and temperature. 63.20.kg, 71.15Mb 2

Thermal conductivity of graphene mediated by strain and size

“…Moreover, unlike the work of Ref. 28, we find qualitatively uniform dependences of k on strain from the full BPE solution and the SMRTA, consistent with that found in strained 3D diamond [40]. Unless specified otherwise, all the results shown below are for N 1 =301 for unstrained and strained is due partly to decreasing magnitude of the anharmonic IFCs with tensile strain [23], which reduces the scattering matrix elements, and partly to the reduction in ZA phonon density of states caused by zone center dispersion linearization [22], which leads to less scatterings of ZA phonons [18].…”

“…Fig.1(a) for which the boundary scattering is neglected totally. Interestingly, the tensile-strain-induced enhancement of k is in contrast to those reported for other carbon-based materials such as 3D diamond [40] and 1D carbon nanotubes [30,45], wherein tensile strains reduce k through phonon softening [45]. While the softening of LA, TA and optic phonons in graphene is indeed observed here, we find hardening of the ZA modes, i.e., higher ZA frequencies and low-frequency group velocities for the strain levels considered.…”

Ab initiothermal transport in compound semiconductors

“…Similar behavior has been previously noted in Si and Ge [7,30]. For systems with very strong N scattering relative to U scattering, such as in diamond [9][10][11], graphene [31,32] and carbon nanotubes [22,33], the full solution to the BTE is required to accurately determine κ L .…”

“…We found that including only 1 st nearest neighbors required very large changes to the anharmonic IFCs in order to enforce the TI conditions and thus was not included here. We have also used a reciprocal-space DFPT approach (black dashed curve) to calculate the anharmonic IFCs and to calculate κ natural , which extends the interactions to 7 th nearest neighbors and includes long range Coulomb interactions [7,[9][10][11][49][50]. As can be seen in Figure 3, the calculated κ natural is fairly insensitive to the nearest neighbor cut-off radius.…”

“…The isotope effect in GaN is very large, with P=68% at T=300K and increases with decreasing temperature as the anharmonic phonon scattering gets weaker. Figure 6 shows previously published [16] calculated isotope effects, P, vs. temperature for cubic GaN (solid black curve), wurtzite GaN (dashed black curve), GaP (green curve), and GaSb (orange curve) with the addition of the calculated P for diamond [11] (gold curve), Ge (red curve), AlSb (brown curve), and 3C-SiC (blue curve). The room temperature P for all the materials studied in this work are also given in Table 1.…”