Limits...
Pressure-induced structural transformations and polymerization in ThC 2

View Article: PubMed Central - PubMed

ABSTRACT

Thorium-carbon systems have been thought as promising nuclear fuel for Generation IV reactors which require high-burnup and safe nuclear fuel. Existing knowledge on thorium carbides under extreme condition remains insufficient and some is controversial due to limited studies. Here we systematically predict all stable structures of thorium dicarbide (ThC2) under the pressure ranging from ambient to 300 GPa by merging ab initio total energy calculations and unbiased structure searching method, which are in sequence of C2/c, C2/m, Cmmm, Immm and P6/mmm phases. Among these phases, the C2/m is successfully observed for the first time via in situ synchrotron XRD measurements, which exhibits an excellent structural correspondence to our theoretical predictions. The transition sequence and the critical pressures are predicted. The calculated results also reveal the polymerization behaviors of the carbon atoms and the corresponding characteristic C-C bonding under various pressures. Our work provides key information on the fundamental material behavior and insights into the underlying mechanisms that lay the foundation for further exploration and application of ThC2.

No MeSH data available.


Related in: MedlinePlus

Calculated (a) enthalpies and (b) volumes per f.u. as a function of pressure for C2/c, C2/m, Cmmm, Immm and P6/mmm phases of ThC2. The enthalpy of Cmmm phase is chosen as zero reference. The inset of (a) is an enlarged detail view for the selected portion by rectangular box. The transition pressures are 3 GPa, 56 GPa, 128 GPa and 203 GPa, and the corresponding abrupt volume collapses are about 9.5%, 11.6%, 2.3% and 2.4%, respectively.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC5382917&req=5

f2: Calculated (a) enthalpies and (b) volumes per f.u. as a function of pressure for C2/c, C2/m, Cmmm, Immm and P6/mmm phases of ThC2. The enthalpy of Cmmm phase is chosen as zero reference. The inset of (a) is an enlarged detail view for the selected portion by rectangular box. The transition pressures are 3 GPa, 56 GPa, 128 GPa and 203 GPa, and the corresponding abrupt volume collapses are about 9.5%, 11.6%, 2.3% and 2.4%, respectively.

Mentions: In order to obtain the transition pressure and transition sequence among these phases, the enthalpy differences as a function of pressure are calculated and presented in Fig. 2(a). It can be seen that the ambient-pressure C2/c phase is the most stable structure below 3 GPa; the C2/m phase becomes more favorable at the pressure ranging from 3 to 56 GPa; the Cmmm phase is stable from 56 to 128 GPa; the Immm phase is stable from 128 to 203 GPa, above which the P6/mmm phase is energetically favorite. The pressure-induced evolution of the unit cell volume for the various phases of ThC2 is calculated and shown in Fig. 2(b). The abrupt volume collapse through each transition are about 9.5%, 11.6%, 2.3% and 2.4% at around 3 GPa, 56 GPa, 128 GPa and 203 GPa, respectively, indicating that these transitions are of the first-order.


Pressure-induced structural transformations and polymerization in ThC 2
Calculated (a) enthalpies and (b) volumes per f.u. as a function of pressure for C2/c, C2/m, Cmmm, Immm and P6/mmm phases of ThC2. The enthalpy of Cmmm phase is chosen as zero reference. The inset of (a) is an enlarged detail view for the selected portion by rectangular box. The transition pressures are 3 GPa, 56 GPa, 128 GPa and 203 GPa, and the corresponding abrupt volume collapses are about 9.5%, 11.6%, 2.3% and 2.4%, respectively.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5382917&req=5

f2: Calculated (a) enthalpies and (b) volumes per f.u. as a function of pressure for C2/c, C2/m, Cmmm, Immm and P6/mmm phases of ThC2. The enthalpy of Cmmm phase is chosen as zero reference. The inset of (a) is an enlarged detail view for the selected portion by rectangular box. The transition pressures are 3 GPa, 56 GPa, 128 GPa and 203 GPa, and the corresponding abrupt volume collapses are about 9.5%, 11.6%, 2.3% and 2.4%, respectively.
Mentions: In order to obtain the transition pressure and transition sequence among these phases, the enthalpy differences as a function of pressure are calculated and presented in Fig. 2(a). It can be seen that the ambient-pressure C2/c phase is the most stable structure below 3 GPa; the C2/m phase becomes more favorable at the pressure ranging from 3 to 56 GPa; the Cmmm phase is stable from 56 to 128 GPa; the Immm phase is stable from 128 to 203 GPa, above which the P6/mmm phase is energetically favorite. The pressure-induced evolution of the unit cell volume for the various phases of ThC2 is calculated and shown in Fig. 2(b). The abrupt volume collapse through each transition are about 9.5%, 11.6%, 2.3% and 2.4% at around 3 GPa, 56 GPa, 128 GPa and 203 GPa, respectively, indicating that these transitions are of the first-order.

View Article: PubMed Central - PubMed

ABSTRACT

Thorium-carbon systems have been thought as promising nuclear fuel for Generation IV reactors which require high-burnup and safe nuclear fuel. Existing knowledge on thorium carbides under extreme condition remains insufficient and some is controversial due to limited studies. Here we systematically predict all stable structures of thorium dicarbide (ThC2) under the pressure ranging from ambient to 300 GPa by merging ab initio total energy calculations and unbiased structure searching method, which are in sequence of C2/c, C2/m, Cmmm, Immm and P6/mmm phases. Among these phases, the C2/m is successfully observed for the first time via in situ synchrotron XRD measurements, which exhibits an excellent structural correspondence to our theoretical predictions. The transition sequence and the critical pressures are predicted. The calculated results also reveal the polymerization behaviors of the carbon atoms and the corresponding characteristic C-C bonding under various pressures. Our work provides key information on the fundamental material behavior and insights into the underlying mechanisms that lay the foundation for further exploration and application of ThC2.

No MeSH data available.


Related in: MedlinePlus