First-principles Investigations On Structural And Physical Properties Of ZrBe₂and ZrZn₂（HfZn₂）

Zr and Zr alloys, which have excellent corrosion resistance, high-temperatureresistance, anti-neutron irradiation and moderate mechanical properties, are widely used inthe processing of precision castings, ceramics, refractories, TV glass and nuclear materials.Therefore, the study of Zr alloys and their performance has an important significance forcivil and military industries. This dissertation is dedicated to explore structural andphysical properties of ZrBe2and ZrZn2(HfZn2) intermetallics from first-principlecalculations based on density functional theory.We have investigated five competing structures (P6/mmm, Fd-3ms, P63/mmc, Immaand Cmcm) for ZrBe2using CASTEP software. Through analysis of the Gibbs free energyand elastic stability dependencies on pressure, the Imma structure was found to beenergetically most stable until around20GPa after which the Cmcm phase became themost stable one. So ZrBe2in the ground state is likely to exist in the Imma structureinstead of P6/mmm obtained in experiments. This discrepancy, in our point, may be causedby the presence of residual tensile stress in ZrBe2during experimental preparation. Tofurther explain the underlying stability mechanism, we perform electronic structurecalculations and find that the Imma and Cmcm structures tend to exhibit greater stabilityunder compression. We also predict that the Fd-3ms structure may be metastable above26GPa. The lattice parameters, compressibility and elastic properties of ZrBe2are alsoestimated. Our calculation results are in agreement with the available experimental andtheoretical data.Besides, a comprehensive investigation of the structural, elastic and thermodynamicproperties for Laves phases ZrZn2and HfZn2were conducted using density functionaltotal energy calculations combined with the quasi-harmonic Debye model. Firstly, thephases of ZrZn2and HfZn2are optimized, so the equilibrium structures are obtained.Further, we estimated the mechanical behaviors of both compounds under compression,including mechanical stability, Young’s modulus, Poisson’s ratio, ductility and anisotropy.Finally, the thermodynamic properties as a function of pressure and temperature areanalyzed and found to be in good agreement with corresponding experimental data.