Atomistic modeling of finite-temperature properties of crystalline β-SiC -: II.: Thermal conductivity and effects of point defects

In this, the second part of a theoretical study of the thermal properties of crystalline beta-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 400 K) where quantum effects become dominant. The effects of carbon and silicon vacancies and antisite defects are studied by introducing a single defect into the simulation cell, allowing the atomic configuration to relax, and then performing heat capacity, thermal expansion and conductivity calculations. We find that the heat capacity and thermal expansion coefficient are affected 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. (C) 1998 Elsevier Science B.V. All rights reserved.