# Kwon Group, Physics, Kyung Hee University

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## Phase Change Materials

A phase change material is a material exhibiting easy and fast transition between crystalline and amorphous phases. Due to this characteristic, phase change materials have been used for rewritable DVDs and Blueray disks, and are expected to be used for phase change random access memory. Ge-Sb-Te compounds are major phase change materials. We are performing molecular dynamics simulations to identify amorphous phases of various Ge-Sb-Te compounds. Our simulation data are analyzed to explore local atomic structures of amorphous phases, which are compared with those of their crystalline counterparts.

### GeTe

We investigate structural properties of varius amorphous phases and crystalline using molecular dynamics simulation. Also, based on a Radial Distribution Functions(RDFs), Angle Distribution Functions(ADFs) and Order Parameters(OPs) analyses, we study local structure characteristics of several phases. Our calculated OPs and RDFs are analyzed and compared to EXAFS data available. Finally, we estimate energy barriers not only between crystalline and one of amorphous phases, but also between different amorphous phases to explore their structural stability, using nudged elastic band method.

### GeSbTe225

The phase transition of Ge2Sb2Te5 between its crystalline and amorphous phases was investigated by constructing its various amorphous phases.

### Sb$_2$Te$_3$

Sb$_2$Te$_3$ is a very interesting material for rewritable optical media. We study of the switching mechanism between the amorphous and crystal states theoretically.