LATTICE-DYNAMICS OF SIC POLYTYPES WITHIN THE BOND-CHARGE MODEL
LATTICE-DYNAMICS OF SIC POLYTYPES WITHIN THE BOND-CHARGE MODEL
复制标题
DOI：
10.1103/physrevb.50.13401
复制
发表时间：
1994-11-01
影响因子：
3.7
通讯作者：
BECHSTEDT, F
中科院分区：
文献类型：
--
作者：
HOFMANN, M;ZYWIETZ, A;BECHSTEDT, F
我们提出了一种现象学方法来研究各种 SiC 多型体的晶格动力学性质。广义键电荷模型适用于立方和六方多型体 3C、6H、4H 和 2H。通过 Ewald 技术充分考虑了离子和键电荷的长程微观电场。短程弹性相互作用通过离子之间的弯曲力和拉伸力以及键的变化来描述。力常数和有效电荷适合拉曼和发光测量已知的声子频率。通过与 3C-和 2H-SiC 的从头计算结果进行比较，不仅测试了频率模型的可靠性，还测试了特征向量的可靠性。我们证明单轴六方多型体的各向异性主要是由于库仑力的非解析性造成的。相应的频率分裂与依赖于键方向的键电荷的轻微变化有关。平行和不平行于六角轴的弹力差异仅是稳定区域边界声子所必需的。讨论了所得频率和态密度的趋势与六方性百分比的关系。考虑了不同声子色散对 3C、6H、4H 和 2H 多型体弹性性能的影响。我们推测通过晶格振动实现多型稳定的可能机制。
We present a phemomenological approach to the lattice-dynamical properties of various SiC polytypes. A generalized bond-charge model is applied to the cubic and hexagonal polytypes 3C, 6H, 4H, and 2H. The long-range microscopic electric field of ions and bond charges is fully taken into account via an Ewald technique. The short-range elastic interactions are described by bending and stretching forces between ions and bond changes. The force constants and effective charges are fit to phonon frequencies known from Raman and luminescence measurements. The reliability of the model is tested not only for the frequencies but also for the eigenvectors by comparison with results of ab initio calculations for 3C-and 2H-SiC. We show that the anisotropy in the uniaxial hexagonal polytypes is mainly due to the nonanalyticity of the Coulomb forces. The corresponding frequency splittings are related to slight changes of the bond charges in dependence on the bond orientation. Differences in the elastic forces parallel and nonparallel to the hexagonal axis are only necessary to stabilize the zone-boundary phonons. The trends of the resulting frequencies and density of states are discussed versus the percentage hexagonality. Consequences of the different phonon dispersions for the elastic properties of the 3C, 6H, 4H, and 2H polytypes are considered. We speculate about possible mechanisms of polytype stabilization by the lattice vibrations.