Metastability relationship between two- and three-dimensional crystal structures: A case study of the Cu-based compounds

TL;DR

This study explores how two-dimensional layer stacking influences the stability of three-dimensional copper-based crystal structures, revealing metastability relationships that could inform computational materials design.

Contribution

It demonstrates a correlation between the stability of 2D and 3D CuX structures and uncovers metastability relationships analogous to elemental metals.

Findings

CuX structures' stability is linked to their 2D layer configurations.

Metastability relationships between different CuX phases are identified.

Total energy pathways for CuX structures are analyzed.

Abstract

Some of the three-dimensional (3D) crystal structures are constructed by stacking two-dimensional (2D) layers. It remains unclear whether this geometric concept is related to the stability of ordered compounds and whether this can be used to computational materials design. Here, using first principles calculations, we investigate the dynamical stability of copper-based compounds Cu$X$ (a metallic element $X$) in the B$_h$ and L1$_1$ structures constructed from the buckled honeycomb (BHC) structure and in the B2 and L1$_0$ structures constructed from the buckled square (BSQ) structure. We demonstrate that (i) if Cu$X$ in the BHC structure is dynamically stable, those in the B$_h$ and L1$_1$ structures are also stable. Although the interrelationship of the metastability between the BSQ and the 3D structures (B2 and L1$_0$) is not clear, we find that (ii) if Cu$X$ in the B2 (L1$_0$) structure is dynamically stable, that in the L1$_0$ (B2) is unstable, analogous to the metastability relationship between the bcc and the fcc structures in elemental metals. The total energy curves for Cu$X$ along the tetragonal and trigonal paths are also investigated.