First-principles Studies On The Crystal Structures And Properties Of Sn_xZn_1-xO Alloys Under High Pressure

As an important functional material of group II-VI metal oxides,Zn O has excellent photoelectric properties and is an ideal material for preparing photoelectric devices.Its band gap is 3.37 e V at room temperature,which is advantageous in the field of short-wavelength luminescence.Exciton binding energy is up to 60 me V,and it can work stably under high temperature or high radiation.Zn O has three excellent characteristics:First of all,zinc oxide has excellent material quality,it is abundant in sources and low in price.Secondly,it has efficient doping properties.Finally,it can be involved in the synthesis of high quality zinc oxide alloy materials.Recent studies show that Sn_xZn_1-xO alloys have a wide application prospect in the fields of photoelectric solar energy conversion and gas sensor,but its crystal structure and physical properties have not been systematically studied,which hinds further research.In addition,pressure is a basic variable that determines the properties of materials,which can change the microstructure,electronic properties and mechanical properties of crystals.It is an effective method to discover new materials and obtain new properties.In order to find the ideal candidate structure of Sn_xZn_1-xO alloys,in this paper,we systematically studied the crystal structure and physical properties of Sn_xZn_1-xO alloys under high pressure based on crystal structure search software and using first-principles calculation method.We systematically searched the crystal structure of Sn_xZn_1-xO alloys in the pressure range of 0-60 GPa using USPEX software package based on genetic evolution algorithm.We predicted a new ground state structure Sn Zn O₂(Cmcm)and several metastable structures,which are Sn Zn₄O₅(I4/mmm),Sn Zn₃O₄(Cm,Cmcm),Sn Zn₂O₃(P4/nmm),Sn₃Zn₂O₅(Imm2),and Sn₂Zn O₃(P-1).All Sn_xZn_1-xO alloys under different stress formation enthalpy calculation show that under atmospheric pressure of the study of crystal structure of thermodynamics are unstable,are metastable structures.With the increase of pressure,we found that the pressure will reduce some alloys formation enthalpy,even turned negative.Thus,we believe that pressure is an effective method to promote the formation of stable Sn O-Zn O alloys.In addition,the phonon spectrum and mechanical properties of crystal structures were calculated to verify the dynamic stability of all structures in the corresponding pressure range,and the elastic constants calculated at atmospheric pressure all meet the mechanical stability conditions.Finally,the electronic and optical properties of Sn_xZn_1-xO alloys are studied by first-principles calculation.Under the action of pressure,Sn_xZn_1-xO alloys have a large tunable band gap,which provides theoretical basis for the preparation and research of materials.We further studied the variation of the optical absorption coefficient of Sn Zn O₂with pressure.With the increase of pressure,the absorption peak moved to the high energy direction.