Structural stability and equation of state of thorium carbide for pressures up to 36 GPa

Abstract

High‐pressure X‐ray diffraction studies have been performed on ThC powder up to 36 GPa. No structural phase transformation has been observed, the rock‐salt structure of ThC being stable over the whole pressure range. The equation of state can be described by the Murnaghan equation with the bulk modulus B0 = 109(7) GPa and its pressure derivative B′0 = 3.1(6). The high‐pressure behaviour of ThC is compared with that of other actinide carbides and nitrides and correlated with the occupation of the 5f electron shell.

A new phase of ThC at high pressure predicted from a first-principles study

“…2 Table 1. The table shows that our calculated constants for the B1 and B2 phases are in very good agreement with the experiments [12,30] and the previous calculations [6,10,16].…”

“…Crystal structure of ThC is a NaCl-type structure (denoted as B1 phase; space group F m3m) at ambient conditions [12], as shown in Fig. 2(a).…”

“…At high pressure, the research on ThC is still limited. Experimentally, Gerward et al and Staun Olsen et al did not observe the structural phase transition from the B1 phase to the B2 phase ( Pm3m) up to 50 GPa [12][13][14]. Recently, Sahoo et al [16] proposed that B1 may be transformed to B2 at around 40 GPa based on their first-principles calculations, however, their dynamical stability was not carefully discussed in their work.…”

“…At ambient conditions, thorium monocarbide (ThC) has a rock-salt type structure (denoted as B1 phase). The structural, electronic, elastic, and thermodynamic properties of the B1 phase have been extensively studied by many groups [5][6][7][8][9][10][11][12][13][14][15][16]. At high pressure, the research on ThC is still limited.…”

First-principle study of B1-like thorium carbide, nitride and oxide

“…a pronounced increase of structural rigidity from metal to carbide due to the direct Th-C bonding formation occurs, as well as for other B1-like metal monocarbides, see [24]. The experimentally estimated ThC bulk modulus B 0 falls in the wide range from 73.9 GPa (the result of extrapolation to stoichiometric ThC 1.0 from the elastic constants c ij , obtained for the ThC 0.063 single crystal [25]) to 107 [22] and 125 GPa (cited in [2]). Thus, in relation to the two last values, our calculations reproduce the experiment with accuracy at about 23-6%.…”