First-principles Study Of The Structural,Elastic,Vibrational,and Optical Properties Of A₂B-type Electrides

In recent years,electrides have attracted great interest in the application of high performance in the field of optoelectronics and catalysis.Especially,as a novel and unique ionic compound,A₂B-type electrides are widely used in high-performance hyperbolic media.In addition,theorists and experimentalists have found many other interesting physical properties in the A₂B-type compounds.For example,A₂B-type electrides have exciting properties such as low work function,high mobility,and high carrier concentration.Through a large number of literature surveys,we found that few people pay attention to their elastic and optical properties,and pay more attention to their electronic properties.Therefore,this paper systematically studies and contrastively analyzes structural,electronic,elastic,vibrational,and optical properties of A₂B（A=Sr/Ba/Li/Na/K;B=P/As/O/S）compounds.The main research contents and innovations are as follows:（1）By calculating the electronic properties of inorganic electrides Sr₂P,Ba₂P and Ba₂As,it finds that they are all metals with strong ionic properties.The elastic properties calculated at atmospheric pressure indicate that they are both mechanically and dynamically stable,and the calculations show that they are anisotropic,with Sr₂P showing weak brittleness and Ba₂P and Ba₂As showing ductility.In addition,the graphical representation of the vibrational properties of Sr₂P indicates that Sr atoms and P atoms have different vibrational intensities（measured by arrow lengths）in different directions.At high frequencies(E_u,A_2u,E modes,etc.),it is mainly contributed by the vibrations of P atoms.This is mainly caused by the huge difference in atomic mass between the Sr and P atoms.Finally,studies of optical properties have shown that the reflectivity and conductivity of Sr₂P are quite different from those of the other two electrides,which may be due to the difference in atomic mass between the metal elements Sr and Ba and the size of the metal ions.This work provides some theoretical references for future exploration of the elastic,vibrational,and optical properties of electrides.（2）A₂O and A₂S（A=Li/Na/K）have anti-fluorite structures.By analyzing the band structure,it is found that all of them are semiconductors except Li₂O,and the band gap value decreases with the increase of the metallicity of metal ions（A=Li,Na,K）.The differential charge density map shows that there are more electrons around an O atom than around an S atom,mainly because the more electron layers an atom has in the same main group,the less attractive the electrons are to the nucleus and the more repulsive the electrons are,the easier it is to lose electrons.Mechanical properties indicate that they are both mechanically stable and their bulk moduli are isotropic.Young’s moduli are anisotropic and the degree of anisotropy increases with the increase of the atomic number of the metal element.Phonon dispersion shows that all of them are dynamically stable,and have the highest frequency at theΓpoint.（3）The structural and elastic properties of Sr₂P and Ba₂P under pressure are calculated.The pressure of 0～5 GPa does not damage the dynamic stability and mechanical stability.From the analysis of the change of lattice constant under pressure,it can be seen that Ba₂P is more easily compressed than Sr₂P,especially the c-axis,mainly because they are both electrides and electrons distributed between layers are not compressive.Interestingly,the anisotropy of Young’s modulus of Sr₂P and Ba₂P gradually decreases with the increase of pressure.Our results provide some reference for the study of structure and elastic properties of high voltage electrides in the future.In this paper,the electronic,elastic,and vibrational properties of several A₂B electrides are systematically compared,which provides a perspective for the study of A₂B electrides.Exploring the physical properties of A₂B type electrides under high pressure has enriched our understanding of the structure and stability of electrides.