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Thermodynamic assessment of the Ba-La-S and Ga-La-S systems

Jiayang Wang, Guangyu Hu, Pierre Lucas, Marat I. Latypov

TL;DR

This study delivers the first CALPHAD thermodynamic assessment of the Ba--La--S and Ga--La--S systems, integrating experimental phase-diagram data with ab initio molecular dynamics results to constrain liquid-phase behavior. It employs substitutional solutions, stoichiometric compounds, liquids with short-range order, and vacancies-enabled sublattice models to build a comprehensive thermodynamic database calibrated against literature and AIMD data. The resulting phase diagrams and thermochemical properties show good agreement with reported data within the investigated composition ranges, and AIMD data help address gaps in liquid data. The work provides a publicly available thermodynamic database and highlights the need for additional high-temperature measurements to extend validity beyond the studied binary and pseudo-binary regions.

Abstract

This paper presents the first thermodynamic assessment of binary and pseudo-binary phase diagrams in the Ba--La--S and Ga--La--S systems by means of the CALPHAD method. Experimental phase diagram equilibrium data and thermodynamic properties available from the literature were critically reviewed and assessed using thermodynamic models for the Gibbs energies of individual phases. The associated solution model was used to describe the short-range ordering behavior of the liquid phases. To supplement the limited experimental data reported in the literature, ab initio molecular dynamics calculations were employed to derive mixing enthalpies of the liquid phases in the binary subsystems. The resulting phase diagrams and calculated thermodynamic properties show good agreement with available literature within the investigated compositional ranges of binary and pseudo-binary systems.

Thermodynamic assessment of the Ba-La-S and Ga-La-S systems

TL;DR

This study delivers the first CALPHAD thermodynamic assessment of the Ba--La--S and Ga--La--S systems, integrating experimental phase-diagram data with ab initio molecular dynamics results to constrain liquid-phase behavior. It employs substitutional solutions, stoichiometric compounds, liquids with short-range order, and vacancies-enabled sublattice models to build a comprehensive thermodynamic database calibrated against literature and AIMD data. The resulting phase diagrams and thermochemical properties show good agreement with reported data within the investigated composition ranges, and AIMD data help address gaps in liquid data. The work provides a publicly available thermodynamic database and highlights the need for additional high-temperature measurements to extend validity beyond the studied binary and pseudo-binary regions.

Abstract

This paper presents the first thermodynamic assessment of binary and pseudo-binary phase diagrams in the Ba--La--S and Ga--La--S systems by means of the CALPHAD method. Experimental phase diagram equilibrium data and thermodynamic properties available from the literature were critically reviewed and assessed using thermodynamic models for the Gibbs energies of individual phases. The associated solution model was used to describe the short-range ordering behavior of the liquid phases. To supplement the limited experimental data reported in the literature, ab initio molecular dynamics calculations were employed to derive mixing enthalpies of the liquid phases in the binary subsystems. The resulting phase diagrams and calculated thermodynamic properties show good agreement with available literature within the investigated compositional ranges of binary and pseudo-binary systems.
Paper Structure (21 sections, 9 equations, 8 figures, 8 tables)

This paper contains 21 sections, 9 equations, 8 figures, 8 tables.

Table of Contents

  1. Introduction
  2. Literature review
  3. Phase diagram data
  4. Thermodynamic data
  5. Ba--S system
  6. La--S system
  7. Ga--S system
  8. Methods
  9. Ab initio molecular dynamics
  10. Thermodynamic modeling
  11. Substitutional solutions
  12. Stoichiometric compounds
  13. Liquid phases with short-range order
  14. Solid solution phase with vacancies and substitution
  15. Optimization methodology
  16. ...and 6 more sections

Figures (8)

  • Figure 1: Representative equilibrium snapshots of the supercells for (a) pure Ba liquid, (b) pure La liquid, and (c) the 50 at.% Ba--La liquid alloy at 1600K, as well as their corresponding PCFs at three time steps.
  • Figure 2: Representative equilibrium snapshots of the supercells for (a) pure Ga and (b) GaS liquids at 1600K; (c) pure La and (d) LaS liquids at 3200K as well as their corresponding PCFs at three time steps.
  • Figure 3: Mixing enthalpy of alloy liquids at various compositions for (a) Ba--La at 1600K, (b) Ga--GaS at 1600K, and (c) La--LaS at 3200K. The mixing enthalpy from the present AIMD simulations (red symbols) and the ensuing CALPHAD assessment (black curves) are seen to be consistent. The inset shows the equilibrium supercell volumes at different compositions under nearly zero internal pressure.
  • Figure 4: Phase diagrams calculated for the Ba--La--S system along with the literature data: (a) Ba--S; (b) Ba--La; (c) La--S; (d) BaS--La2S3. Symbols overlaid with the phase diagram lines represent literature data. The dashed lines represent calculated liquidus lines in regions currently lacking experimental data (and thus require further validation).
  • Figure 5: Thermodynamic properties for the Ba--S binary system: (a) formation Gibbs free energy, (b) enthalpy increment, and (c) heat capacity of BaS; (d) formation enthalpy of the Ba--S phases. Symbols represent literature data: filled for data included in the parameter calibration, open symbols for data shown only for comparison.
  • ...and 3 more figures