Molecular dynamics study of a new metastable allotropic crystalline form of gallium—supertetrahedral gallium

Abstract

A new metastable crystalline form of gallium has been computationally designed using density functional calculations with imposing periodic boundary conditions. The geometric and electronic structures of the predicted new allotrope were calculated on the basis of a diamond lattice in which all carbon atoms are replaced by gallium Ga4 tetrahedra. This form does not have any imaginary phonons, thus it is a metastable crystalline form of gallium. The new form of gallium is a metal and shows high plasticity and low‐melting temperature. Molecular dynamics simulations show that this form of gallium will melt at about 273 K with a sharp increase in temperature in the system during the melting process from 273 to 1800 K. This melting process is very different from conventional melting, where temperature stays the same until complete melting. That unusual melting can be explained by the fact that supertetrahedral gallium is a metastable structure that has an excess of strain energy released during melting. If made this new material may find many useful applications as a new low density metal with stored internal energy. © 2019 Wiley Periodicals, Inc.

Computationally Designed Crystal Structures of the Supertetrahedral Ga4C and Ga4Si Solids

“…1 The calculated density of the cF-Ga 4 C crystal solid (3.49 g/ cm 3 ) is in twice higher than that predicted for the supertetrahedral gallium cF-Ga 8 . 12 Vickers hardness values of cF-Ga 4 C and cF-Al 4 C are the same (Table 1). Also, the calculated Vickers hardness gradually decreases in the order cF-Ga 4 C, cF-Ga 4 Si, cF-Ga 8 .…”

“…The calculated density of the cF -Ga 4 C crystal solid (3.49 g/cm 3 ) is in twice higher than that predicted for the supertetrahedral gallium cF -Ga 8 . Vickers hardness values of cF -Ga 4 C and cF -Al 4 C are the same (Table ).…”

“…Most often these are carbon, boron, aluminum, or gallium atoms. To date, there are molecular supertetrahedral structures based on molecules tetrahedrane C 4 H 4 , cubane C 8 H 8 , [ n ]-prismane C 2 n H 2 n , dodecahedrane C 20 H 20 , and fullerane (hydrogenated fullerene) C 60 H 60 , as well as crystal supertetrahedral structures based on crystal lattice of graphane, diamond, ,,− and lonsdaleite (hexagonal diamond).…”

“…Later, the stability of the infinite crystal structure was also proved . It has been shown theoretically that supertetrahedral boron cF -B 8 , aluminum cF -Al 8 , gallium cF -Ga 8 , and mixed structures cF -B 4 X and cF -Al 4 X (X = C, Si) are also dynamically stable. − All of them should be lightweight materials with a density of less than 1.8 g/cm 3 , and the density of supertetrahedral boron and aluminum should be even less than that of water.…”

Ga4C-family crystals, a new generation of star thermoelectric materials, achieved by band degeneracies, valley anisotropy, and strong phonon scattering among others

“…With different substituents, X 4 Y can be engineered to have semiconductor or metal features, while preserving the key advantages of T-carbon such as low density and high hardness. [30][31][32] In particular, X 4 Y combinations may show much soer phonon dispersions due to the large mass mismatch and weaker covalent bond between X tetrahedra. 33,34 These unique properties and tunability support the view that X 4 Y-family materials may provide a chance to achieve an ultrahigh thermoelectric gure of merit induced by multiple effective physical mechanisms.…”