Phase Relations in the Ni–S System at High Pressures from ab Initio Computations

Abstract

Based on the ab initio calculations within the density functional theory and crystal structure prediction algorithms, the structure and stability of compounds in the Ni−S system at pressures of 100−400 GPa were determined. As a result, a homologous series of discrete compounds (Ni and S) consisting of Ni 14 S-C2/m, Ni 13 S-R3̅ , Ni 12 S-R3̅ , Ni 5 S-C2/m, Ni 4 S-P1̅ , and Ni 3 S-Cmcm is revealed. We also confirmed the absence of the stable Febearing compounds between Fe and Fe 2 S in the studied pressure range. At the Earth's core pressures, 4 wt % of sulfur can be dissolved in solid fcc-Ni without deformation of the structure. Significant deformations in the Ni structure occur at sulfur contents from 4 to 15 wt %. In contrast, up to 0.45 wt % of sulfur could be dissolved in hcp-Fe at 350 GPa and 0 K. For Ni 3 S, two phases with space groups I4̅ and Cmcm were predicted. Ni 3 S-I4̅ is stable at least from 100 GPa, whereas above 330 GPa, it transforms into Ni 3 S-Cmcm. The pressure of phase transition is almost independent of temperature. The Ni 2 S is stable in the entire pressure range and undergoes a single-phase transition from the Pnma-to P6̅ 2m-phase at 266 GPa and 0 K with a Clapeyron slope of 5 MPa/ K. The S-rich sulfide NiS 3 is characterized by Im3̅ m symmetry and is thermodynamically stable from 100 to 318 GPa. Our new data on Ni sulfides might be important to constrain detailed thermodynamic models for Fe−Ni-bearing Earth and planetary cores.

Sulfur-Doped g-C3N4-Supported Ni Species with a Wide Temperature Window for Acetylene Semihydrogenation

“…From another perspective, the lattice spacings of 1.99, 2.00, 2.02, 2.05, 2.06, and 2.07 Å are close to that of Ni (111) (∼2.04 Å), and the lattice spacing of 1.78 Å is close to that of Ni (200) (∼1.76 Å). Density functional theory shows that sulfur can be dissolved in FCC (face-centered cubic) Ni, and the dissolved S atoms can occupy at interstitial and substitutional sites . The former causes the increase of the atom distance and the volume, and the latter causes a slight decrease of the volume.…”