First-principles investigation of the structural and elastic properties of Be₁₂Ti under high pressure

Abstract

The effects of pressure on the structural and elastic properties of Be 12 Ti were investigated by the generalized gradient approximation (GGA) with a Perdew-Burke-Ernzerhof (PBE) exchangecorrelation function using density-functional theory. The calculated lattice parameters at zero pressure and zero temperature are in good agreement with the available experimental data. The pressure dependence of the normalized parameters a/a 0 , c/c 0 , V/V 0 and elastic constants was investigated and it was found that the elastic constants of Be 12 Ti increase monotonically with increasing pressure. By the Born's elastic stability criteria, hexagonal (hcp) Be 12 Ti is mechanically unstable at pressures greater than 41 GPa. The elastic properties such as bulk modulus (B), shear modulus (G), Young's modulus (E) and Poisson's ratio (v) under pressures ranging up to 44 GPa were calculated using the Voigt-Reuss-Hill method. The brittleness and plasticity of the Be 12 Ti alloy were also determined. The Debye temperature and anisotropy under different pressures were also successfully estimated from the calculations.

Resolving the structure of TiBe12

“…Using atomic scale quantum mechanical simulations we have investigated the controversy regarding the crystal structure of TiBe12, originating from papers published between 1952 and 1964. Lattice dynamics simulations for TiBe12 are consistent with the tetragonal structure proposed by Zalkin et al [4] and by Gillam et al [5] (space group I4/mmm), not the hexagonal structure proposed by Raeuchle and Rundle [2] (space group P6/mmm), or the derivative hexagonal sub-cell that has been used recently in modelling studies [6,7]. While larger supercells are investigated, the 54 atom cell was sufficient for calculating the phonon density of states.…”

“…Based on earlier investigation [2][3][4][5], several modern papers equally assume both hexagonal [1,6,7] and tetragonal [8][9][10][11] structures. In particular, most of the modelling efforts have been carried out on the hexagonal structure [6,7].…”

“…Several recent studies [6,7] have used/assumed a sub-cell of the hexagonal crystal structure identified by Raeuchle and Rundle [8] with lattice parameters of a = 4.26 Å and c = 7.33 Å. This differs from the structure defined by the full unit cell in that Ti atoms between alternate sub-cells should be displaced by ±½[0001] in a disordered fashion.…”

First-principles calculations of mechanical and thermodynamic properties of tetragonal Be12Ti

“…12,13 From early literature, more research has focused on experimental aspects for Be 12 Ti, especially for the fabrication and tritium release under normal conditions. [14][15][16][17] Although there are a few theoretical calculations for Be-Ti alloys, they mainly focus on hexagonal Be 12 Ti alloy, 18,19 as for the tetragonal Be 12 Ti, its elastic and thermodynamic properties under high temperature and pressure are missing. Hence, it is necessary to obtain the elastic anisotropy and thermodynamic properties of tetragonal Be 12 Ti alloy at high temperature and high pressure.…”

Retention and diffusion of transmutation H and He atoms in Be12Ti: first-principles calculations

“… 13 Peng et al have conducted theoretical investigations on the structural, elastic and electronic properties under pressure. 14,15 …”