The crystal structures of ThC2

First-principles study of structural, elastic and electronic properties of thorium dicarbide (ThC2) polymorphs

“…As can be seen, for a and c polymorphs our results are very similar to experiments. On the other hand, for tetragonal b-ThC 2 our calculations have overestimated the parameter c (c theor = 6.3826 Å versus c exp = 5.395 À 5.408 Å [5,20]) whereas, the parameter a is underestimated (a theor = 3.8069 Å versus a exp = 4.221 À 4.235 Å [5,20]). This result presumably may be explained taking into account the partial thermal disorientation for C 2 dumbbells (for example, the orientation of a part of the C 2 dumbbells in the plane perpendicular to the c axis, see Ref.…”

“…Thorium dicarbide exists as stoichiometric (C/Th = 2) phase in three polymorphic modifications: low-temperature a-ThC 2 polymorph (up to 1700 K) and two high-temperature polymorphs: b-ThC 2 (in range 1700 K < T < 1754 K) and c-ThC 2 (at T > 1754 K), see [3,5,6].…”

Pressure-induced structural transformations and polymerization in ThC2

“…Under ambient conditions, the ThC 2 has a monoclinic structure (space group C2/c) with four formula units in unit cell1013141521, as shown in Fig. 1(a).…”

“…. Thorium dicarbide has three stoichiometric phases at ambient pressure10131415: monoclinic structure (space group C2/c), stable from room temperature to 1713 K; CaC 2 -tetragonal structure (space group I4/mmm), stable for 1713 K ≤ T ≤ 1768 K; KCN-fcc structure (space group ), stable above 1768 K. In these phases, the carbons group in pairs as C-C dumbbells. The C-C bond in carbon dumbbell has strong covalent character and the carbons present as anions1316.…”

“…Previous research suggests various crystalline structures of ThC under high pressure111218. For ThC 2 , although its structures have been obtained at ambient pressure and high temperature10131415, the structural evolution under high pressure has not been fully understood until now. A clear understanding of the nuclear fuels’ stabilities under extreme conditions is very important for the safe operation of nuclear reactors.…”