Structural Stabilities and Elastic Constants of EuX (X = O, S, Se, and Te) Compounds at High Pressure

Abstract

The structural stabilities, elastic properties and charge transfers of EuX (X = O, S, Se, Te) compounds as a function of pressure are investigated extensively using rst-principles calculations. The ground-state parameters, such as lattice constants, bulk modulus are predicted and compared with the available data, our results are satisfactory. The calculated phase transition pressures from the NaCl-type (B1) structure to the CsCl-type (B2) structure for EuX (X = O, S, Se, Te) also accord with the experiments. Particularly, the elastic constants of EuX (X = O, S, Se, Te) under zero pressure and high pressure are simulated appropriately for the rst time via density functional theory. The softening behaviors of the elastic shear modulus C44 under pressure for the B1 phase of EuX (X = O, S, Se, Te) are captured, which should be responsible for the pressure-induced structural phase transition in the EuX system. It is also suggested that the softening behavior might be induced partly by the p → d and f → d electron transfers of Eu atom under pressure. In addition, the aggregate elastic modulus (B, G, E), Poisson's ratio (σ), Debye temperature ΘD are also successfully obtained for both B1 and B2 phases of EuX.

Rare-earth pnictides and chalcogenides from first-principles

“…Other first-principles approaches have similarly been applied to the Eu chalcogenides. With respect to the structural properties, the agreement between LSDA/GGA studies and experiment tends to be rather good [86], indicating that the fully occupied majority (and minority) band of the Eu 2+ configuration can be reasonably described without taking into account the localized character of the f-electrons. However, as mentioned earlier, the LSDA usually positions the f-band states at the Fermi level, which can result in an unphysical metallic behaviour [87].…”

“…In the neighbouring EuTe, a structural NaCl to CsCl transition is observed at pressures above 10 GPa, but with the exception of an early measurement by Rooymans [157] no indication of a valence transition has been detected up to the pressure of 30 GPa [73,158,159]. A number of different first-principles predictions [86] have been able to model the structural transition, with the calculated pressures ranging from 10 to 17 GPa, depending on the approximation used [86]. Using for example the standard LDA gives a transition pressure of 9.9 GPa [160], compared to 12 GPa when using GGA + Hubbard-I [90].…”

Structural phase transitions of (Bi1−xSbx)2(Te1−ySey)3 compounds under high pressure and the influence of the atomic radius on the compression processes of tetradymites

“…Under high pressure, the B1 structure transforms into a CsCl-type structure (B2, space group Pm-3m), with or without an intermediate phase. [72][73][74][75] The intermediate phases between B2 and B1 phases are different from each other for these materials, depending on the chemical composition.…”

Phase transitions in rare earth tellurides under pressure

“…In good agreement with these latter experimental data, our calculations predict a structural B1 2+ → B2 2+ transition around 13 GPa, with an isostructural B2 2+ → B2 3+ valence transition only setting in at significantly higher pressures of around 47 GPa. A number of theoretical studies have focused on the NaCl to CsCl structural transition in EuTe [47], with calculated transition pressures ranging from 10 to 17 GPa. In these studies exchange and correlation is mostly taken into account at the LDA or GGA level; the rather good agreement with experiment indicates that the electronic structure associated with the fully occupied majority-spin f band of the Eu 2+ configuration can be reasonably described without taking into account the localized character of the f electrons.…”