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HfTa_BCC_SolidSolution_128atoms_VASP6

We performed density functional theory (DFT) calculations for body-centered-cubic (BCC) structures with 128 lattices sites of solid solution binary alloys hafnium-tantalum (Hf-Ta). The electronic structures of alloys have been calculated using Vienna Ab initio Simulation Package (VASP). Within this package the DFT approach is used to reduce many-body Schrodinger equation to set of single particle Kohn-Sham (KS) equations. The generalized electronic exchange-correlation functional is described by generalized gradient approximation with the Perdew-Burke-Ernzerhof parametrization. The electron-ion interactions is described by pseudopotentials developed within the plane-wave basis projector augmented-wave (PAW) approach. These pseudopotentials are available at the VASP portal (http://cms.mpi.univie.ac.at/vasp/). Our calculations have been run with the pseudopotentials treating s and p semi-core states as valence in case for the elements Hf and Ta. The electronic densities and potentials are expanded over plane-waves with energy cutoff of 350 eV. 2x2x2 k-mesh and normal precision were used. The alloys were modeled by supercell containing 128 randomly distributed atoms. At initial step the atoms occupy perfect BCC lattice sites. This initial structure was optimized until energy changes less than 1e-6 eV, while forces acting on atoms don't exceed 1e-2 eV/angstrom. The electron-ion interaction is described by PAW pseudopotentials. The calculations have been collected by sampling chemical compositions across the entire compositional range. The chemical compositions have been sampled by progressively changing the number of atoms per constituent by 4. For each chemical composition of binaries and ternaries, the first-principle calculations have been run for 100 randomized arrangements of the constituents on the BCC lattice sites. We collected data for a total of 3,040 randomized atomic structures over 31 chemical compositions. Further methodological and structural information is contained in the dataset README.txt file.

36 MATERIALS SCIENCE↗

Zr-Hf-Ta fractionation during lunar evolution

Zr/Hf ratios and other elemental data in 68 samples of various mare basalts, KREEP units, and lunar glasses have been determined using instrumental neutron activation analysis coupled with coincidence-anticoincidence counting for greater precision. The data are presented in order to quantify further the amount of Zr/Hf fractionation that has occurred during primordial crystallization and cumulate remelting or by any other process. Models of Zr-Hf evolution are developed to place additional constraints on the bulk lunar composition and on the effects of minor phases that may be responsible for the observed fractionations. The Hf-Ta fractionation in lunar compositions is also reviewed in order to characterize normal Hf(4+) versus Ta(4+) behavior and to delineate possible effects due to the oxidation of Ta(4+) to Ta(5+) during late-stage ilmenite crystallization.

Hughes, S. S.↗

Materials Data on Hf3Ta by Materials Project

Hf3Ta is Uranium Silicide structured and crystallizes in the cubic Pm-3m space group. The structure is three-dimensional. Hf is bonded to eight equivalent Hf and four equivalent Ta atoms to form HfHf8Ta4 cuboctahedra that share corners with twelve equivalent HfHf8Ta4 cuboctahedra, edges with eight equivalent TaHf12 cuboctahedra, edges with sixteen equivalent HfHf8Ta4 cuboctahedra, faces with four equivalent TaHf12 cuboctahedra, and faces with fourteen equivalent HfHf8Ta4 cuboctahedra. All Hf–Hf bond lengths are 3.12 Å. All Hf–Ta bond lengths are 3.12 Å. Ta is bonded to twelve equivalent Hf atoms to form TaHf12 cuboctahedra that share corners with twelve equivalent TaHf12 cuboctahedra, edges with twenty-four equivalent HfHf8Ta4 cuboctahedra, faces with six equivalent TaHf12 cuboctahedra, and faces with twelve equivalent HfHf8Ta4 cuboctahedra.

36 MATERIALS SCIENCE↗

Materials Data on HfTa by Materials Project

HfTa crystallizes in the orthorhombic Cmmm space group. The structure is two-dimensional and consists of two HfTa sheets oriented in the (0, 1, 0) direction. Hf is bonded in a 8-coordinate geometry to four equivalent Ta atoms. All Hf–Ta bond lengths are 2.97 Å. Ta is bonded in a 8-coordinate geometry to four equivalent Hf atoms.

36 MATERIALS SCIENCE↗