First-principles Calculations For Intrincs Defects And Cuprum Doping In Lithium Aluminate

LiAlO₂(LAO)is known to exist three phases in nature,namely,?-LiAlO₂,?-LiAlO₂ and?-LiAlO₂.The?-LiAlO₂ crystal with a single tetragonal structure has received considerable attention because it's stable chemical properties,thermal properties and optical properties which made it widely application.We employ first-principles to calculate the electron structure of the pure?-LiAlO₂ crystal and the defect formation energy and optical properties of?-LiAlO₂ crystal containing point defects.Furthermore,we also calculate the range of the chemical potential of the corresponding elements in LAO crystal,as well as discuss the defect formation energy of intrinsic defects and Cu defects in the range.In chapter one,we introduce the properties,background and our research objective of LAO crystal.In chapter two,we introduce the density functional theory and the principles of the quantum mechanics which is related to our calculations.Then,we introduce the software of the calculations.In chapter three,we employ generalized gradient approximation combined with plane wave pseudo-potential to calculate the electron structure of LAO crystal.For the DFT underestimating the band gap,we adopt HSE method to obtain accurate electron structure.To obtain more accurate charge transition level,we combine a correction scheme proposed by Alkausks to relieve the band edge problem.In chapter four,the FNV-correction is employed to eliminate the artificial interaction between charged defects and the accurate defect formation energy can be obtained.Based on the HSE method and FNV-correction,we present the defect formation energy and charge transition level.Afterwards,we discuss the optical transition according to configuration coordinate diagram.In chapter five,we use the semilocal to calculate the defect formation energy of intrinsic defects of LAO crystal.After two corrections,we describe the optical transition process of intrinsic defects in LAO crystal.Finally,we present normalization emission and absorption spectra for intrinsic defects containing electron-phonon coupling.Comparing the experimental results,we confirm that the absorption peak at 4.5 and5.25e V are assigned to the F center and F⁺center,respectively.And the F center is the origin of the emission peak at 3.02e V.Moreover,our results suggest that the emission peak at 4.06e V reported in early study are caused by and V,_Li center.Also,we speculate that the emission peaks located at 3.84?2.41?1.05?0.83?2.17?3.47 and 1.25e V are assigned to F⁺?O,_i?O,_i,?V,_A,,_l?V,_A,_l?V,_Al and(V_Li-V_O)^�center,which is also the origin of the absorption peaks located at 4.01?3.37?4.41?1.52?2.85?4.02 and 4.40e V.In chapter six,we present the role of Cu on OSL emission.Our results suggest that there is a strong OSL emission of the isolated Cu _Li,however,there is no evidence to suggest that the complex defect Cu _Li-V_Li is involved in OSL response.Not only that,the absorption of Cu _Li-V_Li is located at the effective region of OSL(300-400nm).To validate the emission of Cu _Li was assigned to the 3d¹⁰ to 3d⁹4s¹ inner transitions of Cu⁺ions,we present the density of state to discuss the optical transition,and we confirm the hypothesis.In chapter seven,we discuss the defect formation energy of intrinsic defects and Cu defects as a function of Fermi level under different processing condition.The results suggest that LAO crystal presents n-type semiconductor behavior under O-poor condition,and LAO crystal will present p-type semiconductor behavior under O-rich condition.Combining all the defect formation energy under different condition,we find that Cu will not occupy the Li site under O-poor and Al-poor condition.Furthermore,isolated defect Cu _Li prevails under the rest of the condition.Considering the effect of Cu _Li-V_Li,we find that defect formation energy of isolated Cu _Li is much lower than other Cu defects under O-poor and Al-rich condition.In chapter eight,we make a summary of the full paper.