Speaker
Description
The relative stability of different phases, or their mixtures at finite temperatures, can be estimated by comparing their Gibbs free energies. In the case of disordered phases, such as solid solutions, the primary contribution to the free energy comes from configurational entropy, which arises from the number of ways atoms can be arranged in the system. However, other contributions, such as the vibrational contribution to the free energy, which arises from the system's phonon modes, can significantly influence the stability of a particular solid solution.
As an example of such a system, we examine the Al-Ge binary alloy, which exhibits limited solubility of Ge in Al and almost no solubility of Al in Ge. Since ab initio calculations are typically limited to a relatively small number of atoms, reducing the available configuration space for disordered systems, a machine-learning-based forcefield potential for the Al-Ge alloy was developed. This forcefield was trained on data from smaller-scale ab initio calculations. The trained forcefield potential was then used to calculate the phonon density of states at various temperatures and the corresponding vibrational contributions to the Gibbs free energy across a much broader concentration range. By combining these vibrational contributions with configurational entropy in the total Gibbs free energy, we can estimate the phase stability and solubility limits of the alloy. This approach allows for a more comprehensive estimation of solubility limits, considering not only configurational entropy but also vibrational effects, which are essential for accurately describing the behavior of the Al-Ge system.
