Structural stability of Fe[subscript 5]Si[subscript 3] and Ni[subscript 2]Si studied by high-pressure x-ray diffraction and ab initio total-energy calculations
- MXPL-M
We performed high-pressure angle dispersive x-ray diffraction measurements on Fe{sub 5}Si{sub 3} and Ni{sub 2}Si up to 75 GPa. Both materials were synthesized in bulk quantities via a solid-state reaction. In the pressure range covered by the experiments, no evidence of the occurrence of phase transitions was observed. On top of that, Fe{sub 5}Si{sub 3} was found to compress isotopically, whereas an anisotropic compression was observed in Ni{sub 2}Si. The linear incompressibility of Ni{sub 2}Si along the c axis is similar in magnitude to the linear incompressibility of diamond. This fact is related to the higher valence-electron charge density of Ni{sub 2}Si along the c axis. The observed anisotropic compression of Ni{sub 2}Si is also related to the layered structure of Ni{sub 2}Si, where hexagonal layers of Ni{sup 2+} cations alternate with graphite-like layers formed by (NiSi){sup 2-} entities. The experimental results are supported by ab initio total-energy calculations carried out using density functional theory and the pseudopotential method. For Fe{sub 5}Si{sub 3}, the calculations also predicted a phase transition at 283 GPa from the hexagonal P6{sub 3}/mcm phase to the cubic structure adopted by Fe and Si in the garnet Fe{sub 5}Si{sub 3}O{sub 12}. The room-temperature equations of state for Fe{sub 5}Si{sub 3} and Ni{sub 2}Si are also reported and a possible correlation between the bulk modulus of iron silicides and the coordination number of their minority element is discussed. Finally, we report additional descriptions of these structures, in particular, of the predicted high-pressure phase of Fe{sub 5}Si{sub 3} (the cation subarray in the garnet Fe{sub 5}Si{sub 3}O{sub 12}), which can be derived from spinel Fe{sub 2}SiO{sub 4} (Fe{sub 6}Si{sub 3}O{sub 12}).
- Research Organization:
- Argonne National Lab. (ANL), Argonne, IL (United States). Advanced Photon Source (APS)
- Sponsoring Organization:
- USDOE
- OSTI ID:
- 1006521
- Journal Information:
- Phys. Rev. B, Vol. 77, Issue 2008; ISSN 1098-0121
- Country of Publication:
- United States
- Language:
- ENGLISH
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