Thermodynamic properties of binary HCP solution phases from special quasirandom structures

TL;DR

This paper develops special quasirandom structures (SQS) for binary hcp solutions to accurately model their thermodynamic properties using first-principles calculations, validated against experimental data.

Contribution

It introduces new SQS models for binary hcp solutions that effectively mimic randomness and can be used for first-principles property calculations.

Findings

SQS structures successfully reproduce experimental formation enthalpy.

SQS models accurately predict lattice parameters.

Structures are versatile for studying random hcp alloys.

Abstract

Three different special quasirandom structures (SQS) of the substitutional hcp $A_{1-x}B_x$ binary random solutions ($x=0.25$, 0.5, and 0.75) are presented. These structures are able to mimic the most important pair and multi-site correlation functions corresponding to perfectly random hcp solutions at those compositions. Due to the relatively small size of the generated structures, they can be used to calculate the properties of random hcp alloys via first-principles methods. The structures are relaxed in order to find their lowest energy configurations at each composition. In some cases, it was found that full relaxation resulted in complete loss of their parental symmetry as hcp so geometry optimizations in which no local relaxations are allowed were also performed. In general, the first-principles results for the seven binary systems (Cd-Mg, Mg-Zr, Al-Mg, Mo-Ru, Hf-Ti, Hf-Zr, and Ti-Zr) show good agreement with both formation enthalpy and lattice parameters measurements from experiments. It is concluded that the SQS's presented in this work can be widely used to study the behavior of random hcp solutions.