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Molecular dynamics simulation was used to study the effects of each grain dimension and of grain boundary characteristics on the inter-grain thermal boundary resistance (TBR) and intragrain thermal conductivity of nanocrystalline diamond. The effect of the grain boundaries perpendicular to the heat flow was studied using a multiple slab configuration, which greatly reduced the artifacts associated with the heat source/sink. The TBR between the slabs was found to be more sensitive to the atomic arrangement at the boundary than to the tilt angle between the slabs. When the atomic arrangement at the interface was altered from the minimum energy configuration, the TBR increased by a factor of three, suggesting that a sub-optimal interface quality between the grains could play a large role in reducing the thermal conductivity of nanocrystalline diamond. The thermal conductivity between the boundaries was found to be similar to the bulk value, even when the boundaries were only 25 nm apart. The effect of grain boundaries parallel to the heat flow was found to have a large dependence on the microstructural details. Parallel boundaries which were 2 nm apart reduced the thermal conductivity of defect-free diamond by between one third and a factor of ten. [ABSTRACT FROM AUTHOR]

The lattice thermal conductivity is known to depend on crystal quality, but the reduction in thermal conductivity due to specific defects is presently unclear. Molecular dynamics simulations were used to investigate the impact of microstructural defects on the thermal conductivity of gallium nitride. The conductivity of a finite crystal was reduced to (39 ± 4)% by a screw dislocation density of 2.0 × 1013 cm−2 and to (51 ± 4)% by an edge dislocation of similar density, illustrating that the type of dislocation is important for thermal conductivity. The effect of stacking faults on thermal conductivity was also investigated. [ABSTRACT FROM AUTHOR]