ABSTRACT: Enhanced crystal nucleation in a Sc−Sb−Te phase-change material has enabled subnanosecond switching in phase-change memory devices, making cache-type nonvolatile memory feasible. However, the microscopic mechanisms remain to be further explored. In this work, we present a systematic ab initio study of the relevant parent compounds, namely, Sc2Te3 and Sb2Te3. Despite similar bond lengths and angles in the amorphous phases of the two compounds, Sc2Te3 displays a much more ordered amorphous network without homopolar bonds. As a result, the local structural order in amorphous Sc2Te3 is dominated by square motifs, remarkably similar to those of the metastable rocksalt-like phase. Chemical bonding analysis indicates more robust Sc−Te bonds compared with Sb−Te bonds in the amorphous phase, as well as a substantial role of electrostatic interactions in Sc2Te3 but not in Sb2Te3. The robustness of Sc−Te bonds explains the enhanced nucleation in Sc−Sb−Te compounds. Finally, we discuss an alloying strategy of Sc2Te3 and Sb2Te3 for cache-type Sc−Sb−Te-based phase-change memory.

This work is done by the XJTU-MSE PhD student Getasew M. Zewdie and master student Yuxing Zhou under the supervision of Prof. Wei Zhang from CAMP-Nano. The work received essential support from the national natural science foundation of China, School of International Education, International Office and High-Performance Computing Center of Xi’an Jiaotong University.

The work is published as a Cover paper at Chemistry of Materials this month. G. M. Zewdie, Y.-X. Zhou, L. Sun, F. Rao, V.L. Deringer, R. Mazzarello and W. Zhang*, Chemical design principles for cache-type Sc-Sb-Te phase-change memory materials. Chem. Mater. 31, 4008−4015 (2019). The article can be accessed freely via https://pubs.acs.org/doi/10.1021/acs.chemmater.9b00510