Mechanical and electronic properties of CeO2, ThO2, and (Ce,Th)O2 alloys

A systematic first-principle study is conducted to calculate bulk modulus, elastic constants, phonon-dispersion curves, and electronic structures of CeO2, ThO2, and their ordered binary alloys CexTh8-xO16 with x=1, 2, 4, 6, and 7 using local-density approximation (LDA), generalized gradient approximation (GGA), LDA+U, and GGA+U approaches. In order to get accurate results for these type of systems including f electrons [Ce(4f) and Th(5f)] we optimized the U parameter for use in LDA+U and GGA+U approaches. The computed structural, mechanical, and electronic properties of CeO2 and ThO2 are observed to display strong correlation with experimental data. In particular, the best agreement with experiment is obtained within the LDA+U in which on-site Coulomb interaction parameter (U-eff) for Ce and Th are taken as 6.0 and 5.0 eV. To check the stability of alloy forms, phonon-dispersion curves of CexTh8-xO16 with x=2, 4, and 6 are computed. In all concentrations, mechanical stability conditions are satisfied for alloys. Furthermore, we observed no negative phonon branches in the phonon spectrum of alloys. Our calculations indicated a strong effect of concentration, x, on the electronic structure of CexTh8-xO16.