Dresden 2026 – scientific programme

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MM: Fachverband Metall- und Materialphysik

MM 11: Structurally and Chemically Complex Alloys

MM 11.5: Talk

Tuesday, March 10, 2026, 11:15–11:30, SCH/A215

Accurate temperature-dependent Gibbs free energies of point defects in B2 MoTa — •Xiang Xu¹, Xi Zhang¹, Sergiy V Divinski², and Blazej Grabowski¹ — ¹University of Stuttgart, Stuttgart, Germany — ²Universität Münster, Münster, Germany

Controlling order-disorder motifs is proven to be a key strategy for tuning performance in complex concentrated alloys. To this end, understanding ordered configurations is particularly important, as they represent the theoretical boundary of atomic diffusion, phase stability, and order-disorder phenomena. Since point defects like vacancies and antisites control diffusion and thereby affect ordering and phase evolution, their thermodynamic properties provide critical insight into the fundamental mechanisms behind property tuning. However, difficulties in stabilizing highly ordered refractory phases and the computational complexity of finite-temperature free energy calculations have limited quantitative understanding of their defect thermodynamics. To address this gap, we employ first-principles methods to investigate vacancy thermodynamics in the prototype B2-ordered MoTa alloy systematically. By explicitly accounting for electronic excitations and thermal vibrational contributions, particularly the explicit anharmonicity, we reveal distinct temperature-dependent Gibbs energies for vacancies and antisites in the B2-ordered MoTa. Vibrational pair distribution analysis, performed using an accurate machine-learning potential, demonstrates that the difference in thermal contributions arises from the vibrational phase spaces of the investigated point defects.

Keywords: Refractory alloys; Defect thermodynamics; Density functional theory; B2-ordered compounds; Point defects