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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.


Related in: MedlinePlus

The transformation rate of the occupation number for 7s (left), 6d (middle), and 5f (right) orbitals in Th for Th, ThO and ThO2 as a function of pressure.The black curves represent Th, the red for ThO, and the green for ThO2.
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f2: The transformation rate of the occupation number for 7s (left), 6d (middle), and 5f (right) orbitals in Th for Th, ThO and ThO2 as a function of pressure.The black curves represent Th, the red for ThO, and the green for ThO2.

Mentions: The reaction can be further explained by the the behavior of each reactant and product under pressure. In fact, there are a few studies describing the behavior of Th2728 under pressure. The 5f orbitals are filled at the expense of d electrons were reported therefore whereas the 7s orbital is not discussed specifically. In Fig. 2, we have shown the occupation number of 7s, 6d and 5f orbitals in Th, ThO2 and ThO, respectively. The plots reveal that the occupation number for 5f orbital increases as the occupations in 7s and 6d orbitals decreases as a function of pressure. Moreover, 7s electrons mainly contribute to the transformation compare to 6d electrons. In this regard, it can be linked to that the phase transition of fcc metallic Th (spd metal) to low symmetry bct metallic phase27. Stability of low symmetry bct phase indicates that f electrons are now dominant and participating in bonding. The results related to the transformation of 7s and 6d to 5f have also been reported in literature29. This kind of transformation is not very dominant in the case of ThO and ThO2. It is clear that the most inert phase is the highest oxidation state, i.e. ThO2 (no report of sesquioxide or higher oxidation states), which has the lowest transformation rate to 5f orbital. Naturally, the Th-O interaction alters the original behavior in Th (see further discussions). On the other hand, on the basis of the low occupation in 5f shell, the setting of two boundaries of LDA and PBE is reasonable and further beyond single-particle methods, like LDA + DMFT is not needed. In a nutshell, the distinctive transformations of 7s, 6d and 5f orbitals are correlated to the energies of Th, ThO and ThO2, which determine the enthalpy change.


Stability of a new cubic monoxide of Thorium under pressure.

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

The transformation rate of the occupation number for 7s (left), 6d (middle), and 5f (right) orbitals in Th for Th, ThO and ThO2 as a function of pressure.The black curves represent Th, the red for ThO, and the green for ThO2.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f2: The transformation rate of the occupation number for 7s (left), 6d (middle), and 5f (right) orbitals in Th for Th, ThO and ThO2 as a function of pressure.The black curves represent Th, the red for ThO, and the green for ThO2.
Mentions: The reaction can be further explained by the the behavior of each reactant and product under pressure. In fact, there are a few studies describing the behavior of Th2728 under pressure. The 5f orbitals are filled at the expense of d electrons were reported therefore whereas the 7s orbital is not discussed specifically. In Fig. 2, we have shown the occupation number of 7s, 6d and 5f orbitals in Th, ThO2 and ThO, respectively. The plots reveal that the occupation number for 5f orbital increases as the occupations in 7s and 6d orbitals decreases as a function of pressure. Moreover, 7s electrons mainly contribute to the transformation compare to 6d electrons. In this regard, it can be linked to that the phase transition of fcc metallic Th (spd metal) to low symmetry bct metallic phase27. Stability of low symmetry bct phase indicates that f electrons are now dominant and participating in bonding. The results related to the transformation of 7s and 6d to 5f have also been reported in literature29. This kind of transformation is not very dominant in the case of ThO and ThO2. It is clear that the most inert phase is the highest oxidation state, i.e. ThO2 (no report of sesquioxide or higher oxidation states), which has the lowest transformation rate to 5f orbital. Naturally, the Th-O interaction alters the original behavior in Th (see further discussions). On the other hand, on the basis of the low occupation in 5f shell, the setting of two boundaries of LDA and PBE is reasonable and further beyond single-particle methods, like LDA + DMFT is not needed. In a nutshell, the distinctive transformations of 7s, 6d and 5f orbitals are correlated to the energies of Th, ThO and ThO2, which determine the enthalpy change.

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.


Related in: MedlinePlus