Thermodynamic properties of the Nd-Bi system via emf measurements, DFT calculations, machine learning, and CALPHAD modeling

• Published in: Acta materialia 2022-01, Vol.223 (C), p.117448, Article 117448
• Main Authors: Im, Sanghyeok, Shang, Shun-Li, Smith, Nathan D., Krajewski, Adam M., Lichtenstein, Timothy, Sun, Hui, Bocklund, Brandon J., Liu, Zi-Kui, Kim, Hojong
• Format: Article
• Language: English
• Subjects: CALPHAD modeling; Emf measurement; First-principles calculations; Machine learning; Nd-Bi phase diagram; Rare-earth alloys
• ISSN: 1359-6454; 1873-2453
• DOI: 10.1016/j.actamat.2021.117448

Thermodynamic properties of the Nd-Bi system were investigated using a combination of experimental measurements, first-principles calculations based on density functional theory (DFT), data mining and machine learning (DM + ML) predictions, and calculation of phase diagrams (CALPHAD) modeling. The electromotive force (emf) of Nd-Bi alloys in molten LiCl-KCl-NdCl3 at 773–973 K was measured via coulometric titration of Nd into Bi for the determination of thermochemical properties such as activity coefficients and solubilities of Nd in Bi. A new peritectic reaction of [liquid + NdBi2 = Nd3Bi7] at 774 K was confirmed using differential scanning calorimetry, structural (X-ray diffraction), and microstructural (scanning electron microscopy) analyses. The unknown crystal structure of NdBi2 was suggested to be a mixture of the anti-La2Sb configuration and the La2Te-type configuration based on ML predictions for over 26,000 data-mined AB2-type configurations together with DFT-based verifications. Using the newly acquired experimental data and DFT-based calculations, the thermodynamic description of the Nd-Bi system was remodeled, and a more complete Nd-Bi phase diagram was calculated, including the Nd3Bi7 compound, invariant transition reactions, and liquidus temperatures. [Display omitted]