Atomistic Modeling of Finite - Temperature

In this the second part of a theoretical study of the thermal properties of crystalline-SiC, the thermal conductivity is calculated by using molecular dynamics simulation to evaluate directly the heat current correlation function and thus obtain the conductivity through the Green-Kubo expression in linear response theory. Adopting the same empirical potential model and the temperature scaling method as in part one, we predict absolute conductivity values for a perfect crystal which are in satisfactory agreement with available data, except in the low-temperature region (below 400K) where quantum eeects become important. The eeects of carbon and silicon vacancies and anti-site defects are studied by introducing a single defect into the simulation cell, allowing the atomic connguration to relax, and then performing heat capacity, thermal expansion and conductivity calculations. We nd that the heat capacity and thermal expansion coeecient are aaected very little by point defects even at a high concentration of 0.5%. On the other hand, the thermal conductivity is observed to degrade markedly as a result of the greatly enhanced decay of the heat current correlation, clearly attributable to the dominant mechanism of defect scattering of phonons. The defect simulations also reveal that the conductivity becomes essentially temperature independent. Both characteristics appear to have correspondence with observations on conductivity behavior in neutron-irradiated specimens.