WPI Advanced Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan.
Mathematics for Advanced Materials-OIL, AIST-Tohoku University, Sendai 980-8577, Japan.
Phys Rev Lett. 2018 May 18;120(20):205502. doi: 10.1103/PhysRevLett.120.205502.
The local atomic structures of amorphous Ge-Sb-Te phase-change materials have yet to be clarified and the rapid crystal-amorphous phase change resulting in distinct optical contrast is not well understood. We report the direct observation of local atomic structures in amorphous Ge_{2}Sb_{2}Te_{5} using "local" reverse Monte Carlo modeling dedicated to an angstrom-beam electron diffraction analysis. The results corroborated the existence of local structures with rocksalt crystal-like topology that were greatly distorted compared to the crystal symmetry. This distortion resulted in the breaking of ideal octahedral atomic environments, thereby forming local disordered structures that basically satisfied the overall amorphous structure factor. The crystal-like distorted octahedral structures could be the main building blocks in the formation of the overall amorphous structure of Ge-Sb-Te.
非晶态 Ge-Sb-Te 相变材料的局域原子结构尚未阐明，而且导致明显光学对比的快速晶-非晶相转变也尚未被很好地理解。我们通过专门用于埃米束电子衍射分析的“局部”倒易蒙特卡罗建模，报告了非晶态 Ge_2Sb_2Te_5 中局域原子结构的直接观察结果。结果证实了存在具有岩盐晶体状拓扑结构的局域结构，与晶体对称性相比，这些结构发生了很大的扭曲。这种扭曲导致理想的八面体原子环境被打破，从而形成了基本上满足整体非晶结构因子的局域无序结构。这种类似晶体的扭曲八面体结构可能是形成 Ge-Sb-Te 整体非晶结构的主要结构单元。
