Study On Doping Modification Of P₃N₅ Based On First Principles

P₃N₅ is a binary compound composed of elements of the same main group.Due to the different coordination numbers of P and N,P₃N₅ shows different highly cross-linked structures under normal-pressure(?-)and high-pressure(?-)phase.This highly cross-linked structural feature will bring some potentially excellent properties,such as excellent thermal,mechanical,and chemical stability.P₃N₅ can also be used to synthesize high-performance luminescence materials,which has great application potential in optoelectronic devices.Although P₃N₅ is a potential high-performance material in the future,there are few reports on its structure,electrical and optical properties,and further research is needed.Based on the first-principles calculation method and Material Studio software,the thesis has theoretically studied the lattice structure,band structure,density of states,and optical properties of the intrinsic?-P₃N₅ and?-P₃N₅ materials.The electrical and optical properties of the phosphorous nitride cell with single vacancy defects were also calculated.In this thesis,the P₃N₅ materials at normal pressure and high pressure were modified by substitution doping.and their properties such as structural properties,electrical properties,optical properties,binding energy and electron density difference were calculated.The main research contents and results of this thesis are as follows:(1)Based on the first-principles calculation method and Material Studio software,the structural models of intrinsic?-P₃N₅ and?-P₃N₅ were established.After the convergence test,structural optimization was performed on?-P₃N₅ and?-P₃N₅ to obtain a stable geometric structure.For the optimized P₃N₅ structure,the electrical properties such as the band structure,the density of states,and the optical properties such as the absorption spectrum,energy loss spectrum were calculated.It was found that the intrinsic?-P₃N₅ and?-P₃N₅ are both indirect band gap materials.The band gap of?-P₃N₅ primitive cell is about 3.5 e V,while the band gap of the?-P₃N₅ primitive cell is about 2.6 e V.These two types of P₃N₅ primitive cells have strong absorption intensity in the deep ultraviolet light region.The electrons in the?-P₃N₅ primitive cell tend to inelastically collide with the incident electrons with 22.3e V energy.The electrons in the?-P₃N₅ primitive cell tend to inelastically collide with incident electrons with 8.2 e V and 14.6 e V energy.(2)A single vacancy defect was formed in the intrinsic P₃N₅ primitive cell by deleting an N atom,and first-principles calculations were performed on this type of unit cell.According to calculations,only the normal-pressure Hole1 cell has a band gap of 1.87 e V,and the remaining single vacancy defect cells have conductor properties due to the loss of the band gap.The single vacancy defect cell under normal pressure and high pressure still has relatively strong absorption in the deep ultraviolet region,especially for vacuum ultraviolet rays.(3)In this dissertation,three elements of boron B,aluminum Al,and carbon C were used as impurities when doping the?-P₃N₅ and?-P₃N₅ primitive cells.After doping,it was found that Al had the largest effect on the original lattice structure,C had the least effect,and B had a moderate effect.By calculating the binding energy and the average bond energy of the doped cell,it was found that the stability of the C-doped cell is the best,and the stability of the Al-doped cell is the worst.In the normal-pressure-phase doped cell,B has the most obvious regulation effect on the band gap,followed by Al,while the C-doped cell directly loses the band gap.In the high-pressure phase doped cell,the band regulation effect of B is the most obvious,followed by Al,and the least significant of C.In terms of optical properties,the absorption spectra and energy loss spectra of different doping positions and different doping elements were studied.It was found that the impurities made more absorption peaks and loss peaks appear in both the normal-pressure doped cell and the high-pressure doped cell,and made them became more sensitive to incident photons and incident electrons with lower energy.Doping improves the absorption effect of the cell on visible light with a wavelength of 380 to 780 nm and even infrared light with a wavelength greater than 780 nm.In this thesis,qualitative research on charge transfer is carried out through electron density difference analysis,and population analysis is also used to quantify charge transfer.It is found that Al in the doped cell is positively charged,and B and C are negatively charged.However,C has more charge than B and less than N,which is in line with the law of electronegativity.It was also confirmed that the amount of the charge of the impurity atom is mainly derived from the P atom that is bonded to it.