Study Of Structures And Properties Of Li-Al Alloy

Pressure,temperature and chemical compositions are taken as basic parameters that can change physical and chemical states of materials.Among them,high pressure plays a critical role in accelerating new functional materials discovery and exploring novel performance.High pressure treatment decreases distance between atoms and causes electronic orbital overlap.Moreover,high pressure tends to reduce chemical reaction barrier,contributing to synthesize novel materials easily.Due to light weight,low density and excellent mechanical properties,Li-Al alloys exhibit significant applications in field of aeronautical and space.Previous studies on the Li-Al system mainly focused on the modification of existing materials,but the study on its high-pressure structures has not been reported.In this paper,we systematically investigated the structures and physical properties of Li_xAl?x=1,2,3?in a pressure range from 0 GPa to 100 GPa via CALYPSO software package based on particle swarm optimization combined with first-principles calculations.The results are given as follows:1.The Fd-3m phase of LiAl can be stable at ambient pressure.The enthalpy of the new Pnma phase is very close to that of Fd-3m phase at low pressure.At 26.8 GPa,it will transform to Pm-3m phase,which is thermodynamically stable.In Li₂Al,hexagonal P-3m1?tetragonal I4/mmm phase?orthorhombic Immm phase transition sequences have been found.The phase transition pressures are 19 GPa and51 GPa,respectively.The phase transition sequence of Li₂Al is firstly proposed in our work.For Li₃Al,the phase transition sequence of monoclinic P2₁/m phase??-Li₃Al??-Li₃Al is shown.Meanwhile,phase transition pressures are 28.7GPa and 74.3GPa,respectively.High pressure phase diagrams of Li_xAl?x=1,2,3?have been firstly presented in our work.2.Electron localization function shows that electrons are localized in the form of zero dimension in the framework of LiAl and Li₃Al structures,indicating that they may be potential zero-dimensional electrides.However,with the increase of pressure,the local forms of electrons in Li₂Al are changed from the three-dimensional tubular distribution at ambient pressure to two-dimensional electronic cloud.3.The variation of mechanical stability and elastic constants of Li_xAl?x=1,2,3?system have been studied by VRH method.It is found that the Li-Al alloys are also mechanically stable.Most of the Li_xAl compounds are ductile and show good ductility.