Theoretical Study On The Crystal Structures And Physical Properties Of Li-As And Li-Sb Systems Under High Pressure

Electrides represent a special class of quantum material in which excess valence electrons are located in the interstitial regions acting as anions.Due to the unique interaction between interstitial electrons and orbital electrons,electrides usually exhibit novel properties and extensive applications.Lithium(Li),as the simplest alkali metal element,has good metallicity under environmental pressure;usually loses the outermost s electrons presenting electropositivity in chemical reactions;forms superconducting electrides and some of the compounds have superionic properties under high pressure.Therefore,exploring novel Li-based electrides has become a research topic of interest to researchers in the field of condensed matter physics.Pressure,a basic thermodynamic parameter,can effectively change the bonding mode of atoms,stabilize compounds with unconventional stoichiometries,and also regulate the magnitude and morphology of interstitial electrons in electrides.In addition,the introduction of weakly electronegative elements into high pressure Li metals can stabilize electrides with superconductivity.Therefore,it is important to obtain novel electrides by adjusting pressure and selecting elements.Arsenic(As)and antimony(Sb)are located at the central position of p-block elements,and exhibit moderate electronegativity.Therefore,their reaction with Li is expected to stabilize electrides with novel physical properties under high pressure.In this work,the Li-As and Li-Sb systems have been explored systematically in a wide range of pressures by using first-principles crystal structure prediction calculations.Their high-pressure stable phase diagrams have been established and eleven stable electrides with different interstitial electron morphologies have been proposed.In Li-As system,five superconducting electrides have been identified,which is dominated by the coupling between interstitial electrons or atomic non-s-state(Li 2p,As 4p,and As 4d)electrons and Li-dominated phonons.The relationship between interstitial electron morphology and superconductivity is investigated based on the composition(The models of P6/mmm Li5As and Li8As)and symmetry(The models of Cmc21 and C2/c Li6As)of the structures.In the Li-Sb system,the coexistence of interstitial electronic states,superconductivity,and superionic states is found in C2/m Li11Sb2,and the ultra-low work function of the compound is also found.These results add new members to the family of novel Li-based electrides and provide a scientific reference for the search for polymorphic coexisting compounds.