First-principles Study On The Structure And Physical Properties Of Non-cuprite Type SrCu₂O₂

With the over-exploitation and utilization of non-renewable resources such as coal and oil since the 20th century,the problems of energy shortage and environmental pollution have become increasingly serious and it is urgent to find new visible light responsive photocatalytic materials.Being similar to Cu₂O,the ground state SrCu₂O₂ containing monovalent Cu and O-Cu-O dumbbell structural units is a tetragonal semiconductor,and has potential application in the solution of organic pollutants under visible light degradation.Moreover,SrCu₂O₂ has been proved to have application prospects in the field of optoelectronic materials as a p-type transparent conductive oxide.Based on first-principles calculations,this thesis takes the ground state SrCu₂O₂ as the research object to study its electronic structure and physicochemical properties under doping,defects and pressure.The specific research content is divided into the following three parts:1.The structural,electronic,optical,mechanical,lattice dynamics and electronic transport properties of SrCu₂O₂ crystals were studied using first-principles calculations.The calculated band gap of SrCu₂O₂using the HSE hybrid functional is about 3.33 e V,which is well consistent with the experimental value.The calculated optical parameters show a relatively strong response to the visible light region for SrCu₂O₂.The calculated elastic constants and phonon dispersion indicate that SrCu₂O₂ has strong stability in mechanical and lattice dynamics.The deep analysis of calculated mobilities of electrons and holes with their effective masses proves the high separation and low recombination efficiency of photoinduced carriers in SrCu₂O₂.2.Firstly,by studying the electronic structure of the Ag and N element single-doped SrCu₂O₂,it is found that an appropriate amount of Ag element doping can make the conduction band have a significant downward trend and the higher concentration of N element doping makes the band gap has a downward trend.Further research on the electronic structure of the Ag and N element co-doping system found that the Ag and N element co-doping can effectively reduce the band gap of the system,and the band gap reduction effect is better than that of the single doping at high concentrations.This means that the Ag and N co-doped SrCu₂O₂ has a higher utilization rate of visible light.Secondly,by studying the electronic structure of the system containing copper vacancy and oxygen vacancy,it is concluded that the band gap of the system will be increased when there is only a copper vacancy.The donor energy level will be generated when there is only an oxygen vacancy,which will effectively reduce the band gap of the system with a concentration of 3%-6%.Further research on the electronic structure of the double vacancy system of oxygen anions and copper cations found that the existence of oxygen vacancies can generate a receiver energy level for copper vacancies and effectively reduce the band gap of the system.At high concentrations,the simultaneous existence of oxygen and copper vacancies makes the band gap value of the system significantly lower than that of the system with only oxygen vacancies,which can more effectively enhance the visible light response of the system.3.By studying the transformation process of the phase structure of SrCu₂O₂ under the pressure range of 0-60 GPa,it is found that SrCu₂O₂ transforms from the ground state tetragonal I41/amd structure to the monoclinic C2/c,monoclinic P21/c and monoclinic P2/c structures at 17.2 GPa,24.4 GPa and 52.3 GPa.On this basis,the electronic structure and lattice dynamics properties of the monoclinic C2/c structure at 20 GPa,the monoclinic P21/c structure at 30 GPa and the monoclinic P2/c structure at 55 GPa were studied respectively,and the calculated DFT bandgaps were 0.25 e V,1.30 e V and 0.36 e V.At the same time,the SrCu₂O₂ monoclinic C2/c structure and monoclinic P2/c structure have good static and dynamic stability under their respective pressures,while the monoclinic P21/c structure has certain dynamic instability at 30 GPa,which is a metastable structure.