Vibrational and thermodynamic properties of Ni3S2 polymorphs from first-principles calculations

• Published in: Physics and chemistry of minerals Vol. 38; no. 3; pp. 241 - 249
• Main Authors: Yu, Yonggang G., Ross, Nancy L.
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer-Verlag 01-03-2011; Springer Nature B.V
• Subjects: Anharmonicity; Approximation; Crystallography and Scattering Methods; Density functional theory; Earth and Environmental Science; Earth Sciences; Experiments; First principles; Geochemistry; Gruneisen parameter; High temperature; Mathematical analysis; Mineral Resources; Mineralogy; Nickel sulfide; Original Paper; Orthorhombic phase; Specific heat; Temperature measurement; Thermodynamic properties; Transition pressure; S; Thermal expansion coefficient; Heat capacity; Heazlewoodite; Ni; Vibrational properties; High pressure; Phase transition
• ISSN: 0342-1791; 1432-2021
• DOI: 10.1007/s00269-010-0399-7

We have calculated the compressional, vibrational, and thermodynamic properties of Ni
3
S
2
heazlewoodite and the high-pressure orthorhombic phase (with Cmcm symmetry) using the generalized gradient approximation to the density functional theory in conjunction with the quasi-harmonic approximation. The predicted Raman frequencies of heazlewoodite are in good agreement with room-temperature measurements. The calculated thermodynamic properties of heazlewoodite at room conditions agree very well with experiments, but at high temperatures (especially above 500 K) the heat capacity data from experiments are significantly larger than the quasi-harmonic results, indicating that heazlewoodite is anharmonic. On the other hand, the obtained vibrational density of states of the orthorhombic phase at 20 GPa reveals a group of low-frequency vibrational modes which are absent in heazlewoodite. These low-frequency modes contribute substantially to thermal expansivity, heat capacity, entropy, and Grüneisen parameter of the orthorhombic phase. The calculated phase boundary between heazlewoodite and the orthorhombic phase is consistent with high-pressure experiments; the predicted transition pressure is 17.9 GPa at 300 K with a negative Clapeyron slope of −8.5 MPa/K.