Influence of polytypism on thermal properties of silicon carbide

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Abstract
We present calculations of thermal properties of the 3C, 6H, 4H, and 2H polytypes of silicon carbide (SiC). The underlying lattice-dynamical properties are calculated within a generalized bond-charge model which gives also correct phonon eigenvectors. In the case of the zinc-blende structure the results are checked by comparison with those of ab initio density-functional calculations. Explicitly, we determine the free energy, the specific heat, the Debye temperature, and the Debye-Waller factors. The influence of the polytypism, in particular of the anisotropy in the hexagonal cases, is studied in detail. The theoretical results are in good agreement with available experimental data. A temperature-dependent axial next-nearest-neighbor Ising model is derived. Consequences are discussed for the polytypism and the thermodynamics of the different SiC phases. © 1996 The American Physical Society.

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