Phase Transition And Mechanical Properties Of Hafnium From First-principles

Hafnium and its compounds have excellent physical and chemical properties.They are widely used in the fields of industrial production and nuclear energy.So it is important to study hafnium.we studied the structure transition and transformation path of hafnium under hydrostatic pressure.We also studied the electronic structure,the phonon structure,the thermodynamics properties and the elastic properties of hafnium upon compression.Firstly,we get the basic parameters of the ?,? and ? phase of hafnium.On this basis,the structure transition and transformation path of hafnium under hydrostatic pressure are calculated.Through the calculation of hafnium,we found that hafnium crystallizes are in hexagonal closed-packed(hcp)structure(? phase)at 0 GPa.However,with the pressure gradually increased to 18.77 GPa,a phase transforms to another more open hexagonal structure of ? phase.When the pressure continues to increase to 67.23 GPa,? phase transforms into the body centered cubic structure ? phase.Electronic structure calculations show that the three kinds of Hf are conductors.The 5d orbital of electronic plays a leading role on the conductivity,while the 5p and the 6s orbitals have no contribution to the conductivity of the material.The conductivity of the ?phase of hafnium increases with the increase of pressure.And the conductivity of the ? phase of hafnium decreases with the increase of pressure,while that of the ? phase first decreases and then increases.We also calculate the phonon structure of three kinds under different pressure.Results show that the phonon frequency hafnium increase with the increase of pressure.the ? and ? phase are stable in 0~20 GPa,while the? phase is stable after 76 GPa.In addition,the elastic constants,elastic modulus,elastic wave velocity and other mechanical properties of ?-Hf are found to increase with the increasing of pressure.