Pressure-induced structural transition of ZnO nanocrystals studied with molecular dynamics

TL;DR

This study uses molecular dynamics simulations to explore how ZnO nanocrystals undergo pressure-induced structural transitions, revealing the influence of nanocrystal morphology on the transition pathway and intermediate structures.

Contribution

It provides new insights into the morphological dependence of phase transition pathways in ZnO nanocrystals under pressure.

Findings

Perfect faceted nanocrystals transition through a fivefold intermediate structure.

Surface disorder affects the transition pathway and intermediate structures.

Transition pressure and pathway depend on nanocrystal morphology.

Abstract

We have studied the pressure-induced structural transition of ZnO nanocrystals using constant pressure molecular dynamics simulations for finite system. We have observed the transition from the fourfold coordination wurtzite to the sixfold coordination rocksalt structure, and the process of transition is strongly dependent on the morphology of the nanocrystals. It is found that the perfect faceted ZnO nanocrystals undergo wurtzite to rocksalt transition with a perfect fivefold h-MgO structure as the intermediate status. But for the faceted ones without perfect surface structure, as the number of the atoms removed from the (001) and (00-1) surface edge increases, the local morphology will become more similar to spherical. The nanocrystal will receive equal stress from every direction and it will be more difficult to compress the structure along only c axis as the perfect faceted ZnO nanocrystal. In this situation, only partial structure experiences intermediate fivefold coordination structure or even no intermediate fivefold coordination structure exists dependent on the surface disorder level.