Theoretical Study On The Binary Systems Of Zirconium-Hafnium And Zirconium-Hydrogen At High Temperature And Pressure

Zr-based alloys are widely used in aerospace and nuclear industries for the good resistance to corrosion and low thermal neutron capture cross section. In this work, the structural, mechanism and thermodynamic properties of ZrHf and the crystal structures, electronic structures, phonon dispersions and thermodynamic properties of ZrH2 under high pressure are calculated using the first-principles calculations, providing a theoretical investigation for the design and application of Zr-based alloys in nuclear industry. The main conclusions can be summarized as follows:1. The crystal structures, elastic properties, phonon dispersions, thermodynamic properties and phase stability of ZrHf for different ordered and disordered structures of ZrHf are calculated. The results show that both ordered and disordered structures can coexist and there is no phase transition can spontaneously occur between them (the ordered and disordered structures), which indicates that the performances of ZrHf alloy are independent of atomic arrangements. The properties for the ZrHf alloy are nearly the arithmetic average of Zr and Hf.2. The theoretical properties of ε phase for ZrH2 alloy under high pressure are calculated, including crystal structures, electronic structures, phonon dispersions and thermodynamic properties. The Jahn-Teller effect becomes stronger under high pressure, resulting in the large compression on the direct of the c axis. In addition, a more evident hybridization can be observed below the Fermi level and the pesudogap in also changed under the high pressure. The special vibration property of Zr and H results in a "step" on heat capacity at the room temperature and the heat capacity cannot reach the limit even at 1000 K, which is different from usual material.