Short range order and topology of Te-rich amorphous Ge-Sb-Te alloys

TL;DR

This study investigates the atomic structure of Te-rich amorphous Ge-Sb-Te alloys using neutron and X-ray diffraction, revealing chemical ordering and differences in local structure compared to melt-quenched Ge-Te alloys.

Contribution

The paper provides detailed structural models of Ge-Sb-Te alloys and compares their local order to melt-quenched Ge-Te, highlighting chemical ordering and coordination differences.

Findings

Alloys are chemically ordered with Ge and Sb mainly bonded to Te.

The Te-Te pair correlation is shallower than in melt-quenched Ge-Te.

Ge atoms show stronger separation between first and second coordination shells.

Abstract

The structure of evaporated amorphous Ge$_x$Sb$_x$Te$_{100-2x}$ ($x =$ 6, 9, 13) alloys was investigated by neutron diffraction, X-ray diffraction and extended X-ray absorption spectroscopy (EXAFS) at the Ge, Sb and Te K-edges. Large scale structural models were generated by fitting the experimental datasets (5 for each composition) simultaneously in the framework of the reverse Monte Carlo simulation technique. It was found that the alloys are chemically ordered (Ge and Sb have predominantly Te neighbors) and within the experimental uncertainty each component satisfies the $8-N$ rule. A comparison with the pair correlation functions of melt quenched Ge$_{20}$Te$_{80}$ revealed that the first minimum of $g_{\mathrm{TeTe}}(r)$ is shallower in the ternary alloys than in Ge$_{20}$Te$_{80}$. On the other hand, the separation of the first and second coordination environments of Ge atoms is stronger in the Ge-Sb-Te alloys investigated.