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Stability of a new cubic monoxide of Thorium under pressure.

Sun W, Luo W, Ahuja R - Sci Rep (2015)

Bottom Line: It is found out that the pressure can stabilize the rocksalt phase of ThO, and the transition pressure is estimated between 14 and 22 GPa.The phonon dispersion curves of the rocksalt phase show the positive frequencies which indicates its dynamical stability.Our successful prediction of the stabilization of the metallic ThO has proposed a route to synthesize novel actinide monoxides.

View Article: PubMed Central - PubMed

Affiliation: Department of Material Science and Engineering, KTH-Royal Institute of Technology, Stockholm SE-10044, Sweden.

ABSTRACT
Density functional theory has been applied to elucidate the stability of thorium monoxide (ThO). It is found out that the pressure can stabilize the rocksalt phase of ThO, and the transition pressure is estimated between 14 and 22 GPa. The stability of ThO can be attributed due to the gradually filling 5f orbitals at the expense of 7s and 6d electrons in Th metal. For ThO, the pressure induces stronger Th-O bond reflected by the newly established 6d-2p hybridization which is the dominant cause of its stability. The phonon dispersion curves of the rocksalt phase show the positive frequencies which indicates its dynamical stability. Our successful prediction of the stabilization of the metallic ThO has proposed a route to synthesize novel actinide monoxides.

No MeSH data available.


The band structures of Th, ThO and ThO2 at 20 GPa with the weighted 6d (red) and 5f (green) bands.
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f3: The band structures of Th, ThO and ThO2 at 20 GPa with the weighted 6d (red) and 5f (green) bands.

Mentions: The band structures of Th, ThO and ThO2 at 20 GPa along Γ-X-L-Γ-W directions are shown in Fig. 3, where the 6d and 5f weighted bands are in green and red colors, respectively. The comparison of the 6d bands within these three substances shows that the oxidation on Th leads to a strong excitation to higher energy scale. If the 5f bands in the three substances are compared, it is clear that the oxidation can compress its band width step by step from Th, ThO and to ThO2. Increase in oxidation prompts us to look in to the crystal field effects associated with the ligands, namely the number of oxygen atoms. In the structure of ThO, each thorium atom is surrounded by six oxygen atoms while for ThO2, each thorium atom has eight coordinated oxygen atoms. Hence, we simply employ the crystal field splitting (CFS) that the d/f bands split by a stronger strength in a higher number of coordination number of ligands. Since the 5f bands are becoming narrower with the increase of oxygen atoms per Th atom, the CFS of 5f orbital is marginal in the contrast to that of 6d orbital. This can be explained by the rather small occupation number of 5f orbital, therefore 6d orbital is the core of the oxidation. In ThO2, we observe one more interesting finding is that the valence band maximum are located at two points along Γ-X and Γ-W direction and the conduction band minimum are located at X-L and Γ-W direction. It will be very interesting to investigate the absorption spectrum of ThO2 to see whether the higher oxidation compound, ThO2 having a large band gap is due to the stronger 6d CFS or not.


Stability of a new cubic monoxide of Thorium under pressure.

Sun W, Luo W, Ahuja R - Sci Rep (2015)

The band structures of Th, ThO and ThO2 at 20 GPa with the weighted 6d (red) and 5f (green) bands.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4559911&req=5

f3: The band structures of Th, ThO and ThO2 at 20 GPa with the weighted 6d (red) and 5f (green) bands.
Mentions: The band structures of Th, ThO and ThO2 at 20 GPa along Γ-X-L-Γ-W directions are shown in Fig. 3, where the 6d and 5f weighted bands are in green and red colors, respectively. The comparison of the 6d bands within these three substances shows that the oxidation on Th leads to a strong excitation to higher energy scale. If the 5f bands in the three substances are compared, it is clear that the oxidation can compress its band width step by step from Th, ThO and to ThO2. Increase in oxidation prompts us to look in to the crystal field effects associated with the ligands, namely the number of oxygen atoms. In the structure of ThO, each thorium atom is surrounded by six oxygen atoms while for ThO2, each thorium atom has eight coordinated oxygen atoms. Hence, we simply employ the crystal field splitting (CFS) that the d/f bands split by a stronger strength in a higher number of coordination number of ligands. Since the 5f bands are becoming narrower with the increase of oxygen atoms per Th atom, the CFS of 5f orbital is marginal in the contrast to that of 6d orbital. This can be explained by the rather small occupation number of 5f orbital, therefore 6d orbital is the core of the oxidation. In ThO2, we observe one more interesting finding is that the valence band maximum are located at two points along Γ-X and Γ-W direction and the conduction band minimum are located at X-L and Γ-W direction. It will be very interesting to investigate the absorption spectrum of ThO2 to see whether the higher oxidation compound, ThO2 having a large band gap is due to the stronger 6d CFS or not.

Bottom Line: It is found out that the pressure can stabilize the rocksalt phase of ThO, and the transition pressure is estimated between 14 and 22 GPa.The phonon dispersion curves of the rocksalt phase show the positive frequencies which indicates its dynamical stability.Our successful prediction of the stabilization of the metallic ThO has proposed a route to synthesize novel actinide monoxides.

View Article: PubMed Central - PubMed

Affiliation: Department of Material Science and Engineering, KTH-Royal Institute of Technology, Stockholm SE-10044, Sweden.

ABSTRACT
Density functional theory has been applied to elucidate the stability of thorium monoxide (ThO). It is found out that the pressure can stabilize the rocksalt phase of ThO, and the transition pressure is estimated between 14 and 22 GPa. The stability of ThO can be attributed due to the gradually filling 5f orbitals at the expense of 7s and 6d electrons in Th metal. For ThO, the pressure induces stronger Th-O bond reflected by the newly established 6d-2p hybridization which is the dominant cause of its stability. The phonon dispersion curves of the rocksalt phase show the positive frequencies which indicates its dynamical stability. Our successful prediction of the stabilization of the metallic ThO has proposed a route to synthesize novel actinide monoxides.

No MeSH data available.