The influence of carbon non-stoichiometry on the electronic properties of thorium monocarbide ThC

The first-principle band structure calculations are employed to examine the influence of carbon non-stoichiometry on the structural and electronic properties of the cubic thorium monocarbide ThC. As a result, the equilibrium geometries, electronic bands, densities of states (DOS), Sommerfeld constants and Pauli paramagnetic susceptibility for ThC_1?x (where x = 0, 0.25 and 0.50) are obtained and analyzed in comparison with available experimental data. Additionally, the formation energies of carbon vacancies are theoretically estimated for ThC_1?x.The results obtained indicate that the introduction of carbon vacancies in ThC is accompanied by pronounced DOS changes due to the appearance of novel “vacancy states” in the near-Fermi region formed by comparable contributions of Th 6d and 5f states. The carbon deficiency strongly affects the structure and stability of thorium carbide. For example, for the hypothetical “over-deficient" composition ThC_0.50 the initial cubic structure undergoes significant tetragonal distortions. On the contrary, for ThC_0.75 the value of E_vf is positive and the cubic structure of this phase is preserved.