Structural, electronic and hyperfine properties on Sm2O3, Eu2O3 and Gd2O3 phases

Abstract

We present a detailed first-principles study of three rare-earth lanthanide sesquioxides (Ln2O3, Ln = Sm, Eu, and Gd) in the hexagonal A, the monoclinic B, and the cubic C phases. The calculations were performed with the Density Functional Theory (DFT)-based Augmented Plane Wave plus local orbital (APW + lo) method, using the local spin density approximation (LSDA) and the LSDA + U approach to take into account the strongly correlated Ln-4f electrons. We calculated the equilibrium structures and the effect of hydrostatic pressure on them, the density of states (DOS), the energy band-gaps and, finally, the electric-field-gradient (EFG) tensor at the different cationic sites. The obtained predictions reveal that for the three considered Ln2O3 sesquioxides, the C phase is the stable one, with a transition pressure to the A phase of about 1–2 GPa. For each Ln2O3, the predicted properties were compared with those obtained by means of different experimental techniques. We found that the crystal equilibrium volume, bulk modulus and its first pressure derivative obtained with LSDA are in good agreement with previous experimental results. On the other hand, the inclusion of the U term gives a correct description of the insulating ground state of these systems. Concerning the EFG tensor, LSDA and LSDA + U predict similar values for the EFG at each cationic site in all cases. These results are consistent with the hyperfine interactions experiments reported for the B and C phases of Gd2O3. Finally, we analyze the origin of the EFG at Ln sites, by considering the contributions of the different Ln orbitals to it, and its relation with the local structure.