Properties of hexagonal Al2Ge2RE (RE=Y,La,Ce,Nd,Eu,Gd,Tb,Y b and Lu) : A first-principles study

In this work, we present a study of the structural, elastic and electronic properties of the Al2Ge2RE (RE=Y, La, Ce, Nd, Eu, Gd, Tb, Yb and Lu) through the approaches of generalized gradient approximation (GGA) and local spin density approximation with the Hubbard energy (LSDA+U) based on density-functional theory. For most of the compounds (RE=Y, La, Ce, Nd, Eu, Yb and Lu), the results of the structural constants calculated from the approach of LSDA+U are in good agreement with the reported experimental data. Both the approaches of GGA and LSDA+U have been used to calculate DOS. Compared with the results of the GGA approach, the LSDA+U is more credible because it can show the influence of RE-f states and the RE-f states play an important role in the compound. The magnetic property has been investigated according to the result of DOS and it shows that the Al2Ge2Y, Al2Ge2La, Al2Ge2Y b and Al2Ge2Lu do not exhibit obvious magnetic property, while the other five ternary compounds are magnetic. The Voigt–Reuss–Hill (VRH) approach is used to calculate the elastic properties including bulk and shear moduli. The results of the calculated Poisson’s ratio ν and the B/G ratio demonstrate that all the Al2Ge2RE ternary compounds are brittle materials. The compounds, i.e. Al2Ge2Nd, Al2Ge2Eu, Al2Ge2Gd and Al2Ge2Tb which are mechanically unstable, display differences with the other five in the elastic properties.