Dynamics Study Of Doped High Temperature Wave Transparent Si₃N₄ Ceramic Materials

Silicon nitride ceramics have great application potential in the field of new generation of high temperature wave transparent materials due to their good thermal stability and ablation resistance,and have become an important research subject in the field of scientific research and industry.However,as a wave transparent material,intrinsic silicon nitride has a high dielectric constant,which is not conducive to its microwave transparent at high temperature.Therefore,silicon nitride ceramics need to be modified to improve their high-temperature wave transparent properties,doping heterogeneous elements is one of the important method to expand their intrinsic properties.In the aspect of studying the wave transparent properties of silicon nitride materials,researchers found that silicon nitride materials would be oxidized in high temperature environment,and there were also some problems such as high temperature thermal radiation,which made the performance measurement effect of silicon nitride materials under high temperature environment usually not ideal.Hence,the computer simulation method naturally became the best way to study the high temperature modification of silicon nitride materials.In this paper,the wave transparent properties of doped ?-Si3N4 are studied,and the theoretical calculation method is used to start from three basic research contents:first,to explore the simulation calculation method su,itable for the molecular level of high temperature silicon nitride structure;second,to find a simulation method to improve the comprehensive properties of silicon nitride transparent materials;third,to study the influence of temperature field on the high temperature transparent properties of silicon nitride structure.The main results are as follows:(1)The first-principles-based numerical calculation method is used to optimize the geometric structure of silicon nitride by systematically testing the calculation strategy and key calculation parameters.The basic parameters such as electronic structure,wave transparent properties and elastic constants under ground state are calculated.The calculated results are in good agreement with the experimental data,which shows that the calculation method and parameter settings adopted in this paper are correct and credible for predicting the high temperature micwave transparent performance of doped ?-Si3N4 structure.(2)Improving the transmittance of silicon nitride structure by doping B and O elements.In this paper,seven doping models are designed and optimized.The calculation results show that the B-O co-doped structure is easier to form stable doping structure,and can improve the wave transparent and structural properties of silicon nitride structure.Among them,B-O para-substituted co-doped structure is considered to be a kind of silicon nitride-based Si-B-O-N transparent material system with excellent comprehensive properties.(3)The first-principles molecular dynamics method was used to simulate the structural properties of the supercell structure of ?-Si3N4 and the B-O para-substituted co-doped structure at 500-2000K,and the related wave transparent properties of the structures at different temperatures were calculated.The simulation results show that with the increase of temperature,the properties of the supercell structure of ?-Si3N4 decrease sharply at temperatures above 1500K,while the B-O counterposition substitution doping structure still maintains good structural stability and excellent wave transparent performance at these temperatures.In summary,in order to improve the high-temperature wave transparent performance of the structure of ?-Si3N4,a systematic dynamic study has been carried out in this paper.The calculated results of the ground state properties of the structure are in good agreement with the experimental values.Through element doping,the wave transparent performance of silicon nitride material has been adjusted and improved theoretically.At the same time,the calculation results under high-temperature conditions show that the doping system can effectively improve the silicon nitride material.The high temperature wave transparent property of the material.This paper enriches the research and development methods of high temperature transparent materials,and has practical significance for the application of Computational Materials Science in the field of modern high temperature transparent materials research and development.