Abstract
The elastic, thermodynamic, and electronic properties of fluorite RuO_2 under high pressure are investigated by plane-wave pseudopotential density functional theory. The optimized lattice parameters, elastic constants, bulk modulus, and shear modulus are consistent with other theoretical values. The phase transition from modified fluorite-type to fluorite is 88 GPa (by localized density approximation, LDA) or 115.5 GPa (by generalized gradient approximation, GGA). The Young's modulus and Lam\'e's coefficients are also studied under high pressure. The structure turned out to be stable for the pressure up to 120 GPa by calculating elastic constants. In addition, the thermodynamic properties, including the Debye temperature, heat capacity, thermal expansion coefficient, Gr\uneisen parameter, and Poisson's ratio, are investigated. A small band gap is found in the electronic structure of fluorite RuO_2 and the bandwidth increases with the pressure. Also, the present mechanical and electronic properties demonstrate that the bonding nature is a combination of covalent, ionic, and metallic contributions.
Highlights
Attractions to study RuO2 are due to its fundamental properties and potential superhard characteristics [1, 2]
Pseudo atomic calculations have been performed for Ru (4s24p64d 75s1) and O (2s22p4), where the self-consistent convergence of the total energy is at 5.0 × 10−7 eV/atom
The current investigations revealed that the fluorite RuO2 is a potential ultrahard material
Summary
Attractions to study RuO2 are due to its fundamental properties and potential superhard characteristics [1, 2]. Elastic properties focusing on Pa3 ̄ phase of RuO2 have been investigated systematically [2, 7]. Electronic structures [8,9,10,11] and optical properties [12,13,14] of rutile and orthorhombic [14] RuO2 have been extensively studied. The hardness and elasticity in cubic RuO2 and Raman scattering of the rutile-to-CaCl2 phase transition have been probed experimentally [16]. Previous investigations on fluorite RuO2 are not complete and some problems remain unresolved. Many properties, such as the hardness, stabilization, elastic and thermodynamic properties etc under high pressure, are still unknown. To reveal the superhard characteristics appropriately, a detailed theoretical description of the elastic and electronic properties is necessary
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