Encyclopedia of Crystallographic Prototypes

α-Ni$_{7}$S$_{6}$ Structure: A9B5_oC56_63_c4f_c2f-001

• This structure goes by various names: (Pearson, 1967) calls it Ni$_{6}$S$_{5}$, while (Villars, 2018) calls it Ni$_{5.6}$S$_{4.9}$ or $\gamma$–Ni$_{7}$S$_{6}$. This confusion exists because most of the sites are only partially occupied:
  • The Ni I (4c) site has 96.5% occupation.
  • The S I (4c) site is fully occupied.
  • The Ni II (8f) site has 43.6% occupation.
  • The Ni III (8f) site has 91.9% occupation.
  • The Ni IV (8f) site has 51.8% occupation.
  • The Ni V (8f) site has 45.9% occupation.
  • The S I (8f) site has 98.5% occupation.
  • The S II (8f) site has 94.5% occupation.
• Thus the stoichiometry of this system is Ni$_{22.516}$S$_{19.440}$, Ni$_{7}$S$_{6.044}$, or Ni$_{5.6}$S$_{4.83}$. Allowing for rounding, Ni$_{7}$S$_{6}$ seems to be the best choice.
• (Villars, 2018) gives this as a high-temperature structure, stable in the range 520-800K, with the exact boundaries depending on the composition.
• (Fleet, 1972) gives the structure in the $Bmmb$ setting of space group #63. We used FINDSYM to transform this to the standard $Cmcm$ setting.

Base-centered Orthorhombic primitive vectors

References

• M. E. Fleet, The Crystal Structure of α-Ni$_{7}$S$_{6}$, Acta Crystallogr. Sect. B 28, 1237–1241 (1972), doi:10.1107/S0567740872004029.
• W. B. Pearson, A Handbook of Lattice Spacings and Structures of Metals and Alloys, Volume 2, International Series of Monographs on Metal Physics and Physical Metallurgy, vol. 8 (Pergamon Press, Oxford, London, Edinburgh, New York, Toronto, Sydney, Paris, Braunschweig, 1967).
• P. Villars, H. Okamoto, and K. Cenzual, eds., ASM Alloy Phase Diagram Database (ASM International, 2018), chap. Nickel-Sulfur Binary Phase Diagram (1990 Singleton M.). Copyright © 2006-2018 ASM International.

Found in

• R. T. Downs and M. Hall-Wallace, The American Mineralogist Crystal Structure Database, Am. Mineral. 88, 247–250 (2003).

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