title: High-pressure polymorphs of Li(2)BeH(4) predicted by first-principles calculations.
abstract: We report two orthorhombic high-pressure polymorphs of β- Na(2)SO(4)- and La(2)NiO(4)-type structures for lithium beryllium hydrides (Li(2)BeH(4)) predicted by first-principles calculations. The β- Na(2)SO(4)-type structure possesses BeH(4) tetrahedra, similar to the zero-pressure α-Li(2)BeH(4) structure, but in dramatic contrast to the peculiar BeH(4) octahedral layer in the La(2)NiO(4)-type structure. The β- Na(2)SO(4)-type structure energetically surpasses the α-Li(2)BeH(4) structure for stability above 7.2 GPa, which is nicely correlated with the experimental transition pressure of 9.1 GPa. Further transformation to the La(2)NiO(4)-type structure is predicted at 28.8 GPa. The two transitions are identified as first-order in nature with volume contractions of 3.32% and 5.17%, respectively. Our current discovery has ruled out the previously proposed Cs(2)MgH(4)-type structure as the candidate for the high-pressure phase.
authors.affiliation: State Key Laboratory of Superhard Materials, Jilin University, Changchun 130012, People's Republic of China.
authors.forename: Hui
authors.initials: H
authors.lastname: Wang
authors.forename: Quan
authors.initials: Q
authors.lastname: Li
authors.forename: Yanchao
authors.initials: Y
authors.lastname: Wang
authors.forename: Guoying
authors.initials: G
authors.lastname: Gao
authors.forename: Yanming
authors.initials: Y
authors.lastname: Ma