| Zirconium and its alloys have attracted great attention in the field of scientific research, as well as a variety of civil and military industries due to their unique properties such as anti-neutron irradiation, corrosion resistance, low density and so on. This dissertation is dedicated to explore structural and physical properties of ZrSi2 and ZrB4 from first-principles calculations combined with the quasi-harmonic Debye model.In this work, structural, elastic, electronic and thermodynamic properties of ZrSi2 under different temperatures and pressures have been investigated. The elastic constants and elastic modulus indicate that ZrSi2 is mechanically stable up to 80 GPa and there is a transition from brittle to ductile nature at about 56.5 GPa. The calculated elastic anisotropy factors suggest that ZrSi2 is anisotropic and the degree increases with pressure.The calculated energy band structure, charge density distribution and Mulliken populations unraveled that there are ionic, covalent and metallic bonding in the crystal.The discussions of specific heat, thermal expansion coefficient and so on point out that pressure and temperature have manifest effects on these thermodynamic properties.Besides, the recently predicted ZrB4 with Amm2 orthorhombic structure has great scientific and technical significance owing to its novel B-Zr-B “sandwiches” layers bonding and evaluated high hardness. To better understand the performance of Amm2-ZrB4, its elastic and thermodynamic properties under pressure and temperature are studied here. It is found that ZrB4 keeps brittleness and mechanical stability up to 100 GPa, possessing pronounced elastic anisotropy demonstrated by the direction-dependent Young’s modulus, shear modulus and Poisson’s ratio. The pressure and temperature dependences of the thermodynamics parameters including normalized volume V/V0, bulk modulus, specific heat, Debye temperature, thermal expansion coefficient and Grüneisen parameter are obtained and discussed detailedly. |
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