PHONONS IN AX2 GLASSES - FROM MOLECULAR TO BAND-LIKE MODES
PHONONS IN AX2 GLASSES - FROM MOLECULAR TO BAND-LIKE MODES
复制标题
DOI：
10.1103/physrevb.15.4030
复制
发表时间：
1977-01-01
影响因子：
3.7
通讯作者：
THORPE, MF
中科院分区：
文献类型：
--
作者：
SEN, PN;THORPE, MF
我们研究了玻璃态 A X 2 系统的振动密度，例如 SiO 2 和 Ge S 2，它们由连接在一起形成随机网络的四面体组成。我们表明，具有单个最近邻中心力的模型可以很好地表示高频模式。该模型导致振动模式与 Weaire 和 Thorpe 研究的四面体网络的电子特性同构。这使我们能够研究振动模式从分子状到带状的转变，作为 AXA 键角和质量的函数。找到了描绘允许的频率区域和模式特征的频谱限制。这些与随机网络的详细性质无关。对于 AXA 键角的两个极限（即 90 度和 180 度），考虑了非中心力的影响。我们得出的结论是，当 AXA 键角接近 90°且角力较弱时，可以将无定形网络视为弱相互作用分子单元的组装体。我们将Be F 2 、Ge S 2 和Ge Se 2 归类为以分子效应为主，而固态效应在Si O 2 和Ge O 2 中最为重要。
We study the vibrational density of states of glassy A X 2 systems such as Si O 2 and Ge S 2 which consist of tetrahedra linked together to form a random network. We show that the higher-frequency modes can be well represented by a model with a single-nearest-neighbor central force. This model leads to an isomorphism of the vibrational modes to the electronic properties of the tetrahedral network studied by Weaire and Thorpe. This allows us to study the metamorphosis of the vibrational modes from molecular-like to band-like as a function of the AXA bond angle and the masses. The spectral limits delineating the allowed frequency regions and the character of the modes are found. These are independent of the detailed nature of the random network. The effect of a noncentral force is considered for the two extreme limits of AXA bond angles (ie, 90 and 180). We conclude that it is justified to consider an amorphous network as an assembly of weakly interacting molecular units when the AXA bond angle is close to 90 and the angular forces are weak. We classify Be F 2, Ge S 2, and Ge Se 2 as being dominated by molecular effects, whereas the solid-state effects are most important in Si O 2 and Ge O 2.