Scandium, Yttrium And Erbium Metal Hydrogen, Helium In The Behavior Of The Density Functional Theory Study

Rare earth metals, an efficient and convenient hydrogen storage materials, canabsorb a large number of hydrogen (H) atoms and its isotopes, forming correspondingmetal hydrides, deuterides and tritides. Among rare earth metals, scandium (Sc), yttrium(Y) and erbium (Er) are of interest for their high-capacity H storage and differentelectronic structures. The research on the behavior of H and He in Er is more than thosein Sc and Y and the in-depth and systematic study of H and He in Sc, Y and Er are rare.Therefore, in order to learn more about the behavior of H and He in Sc, Y, Er metalsand metal hydrides, it is necessary for us to make a comparative and systematic researchon H and He in Sc, Y, Er metals and metal hydrides.Because of the the rapid development of computing power, ab initio calculationsbased on density functional theory (DFT) have gradually developed into an importantresearch methods in material simulations. Ab initio calculations have been performed toinvestigate the behavior of H and He in β-phase Sc, Y, Er metals and metal hydrides.The present studies include the following four aspects.(1) Ab initio calculations have been performed to investigate the behavior of Hpoint defects in hcp Sc, Y and Er metals. The results show that the occupiedpositions of H point defects in hcp Sc, Y and Er metals follow the sequence oftetrahedral interstial, octahedral interstitial and substitutional. The density of statesindicates that the negative formation energies of interstitial H atoms are maybeattributed to.the hybrid and strong interaction between the interstitial H atoms and theirneighbor metal atoms(2) The behaviors of He point defects in hcp Sc, Y and Er metals have beeninvestigated by ab initio calculations. The results indicate that the occupiecd positionsof He point defects in hcp Sc, Y and Er metals follow the sequence of substitutional,tetrahedral interstitial and octahedral interstitial. He point defects prefer to occupysubstitutionals in hcp metal, which is the same as thoese in most bcc and fcc metals. Thetetrahedral interstitials for He point defects are more favorable than the octahedralinterstitials, which is similar to that in most bcc metals, but different to that in fcc metals. Therefore, the occupiecd position of He point defects in the metals may be related to thestructure of metals.(3) The climbing image nudged elastic band (CI-NEB) method has been performedto investigate the migrations of hydrogen atoms in β-phase scandium, yttrium anderbium hydrides with three different H/metal ratios. The results show that the migrationmechanisms of H atoms are the same for the same H/M(M=Sc、Y、Er)ratio, but themigration barriers increase with the increasing of host-lattice atomic number.In addition, we found that the formation energies of Hoct/Vtetpairs in β-phase MH2(M=Sc, Y, Er) depend slightly on the metals in MH2, but significantly on the crystalstructures of these β-phase metal hydrides.(4) The three different migration mechanisms of helium atoms in β-phasescandium, yttrium and erbium hydrides have been studied by CI-NEB. The results showthat the migration mechanisms of He atoms in β-phase scandium, yttrium and erbiumhydrides are different. The favorable migration mechanism of He depends slightly onthe Vtetin Sc hydride, but strongly on that in Y and Er hydrides, which may account forthe different behavior of initial He release in ScT2and ErT2.