Study On The Structure Design And The Heat Resistance Of Boron-doped Diamond

Diamond is a special material with outstanding performance which is used in mechanical,thermal,optical,chemical,electronic products.etc.After doped boron,diamond has outstanding advantages in the oxidation resistance,chemical inertness and semiconductor performance.The poor thermal stability of the conventional diamond under high temperatures tends to make some performance degradation and sometimes even a completely loss.So the heat resistance of diamonds is very important for the performance index.This topic is based on the first principles,using the density functional theory,and analyzing the boron-doped diamond mixed with the 1-4 boron atom respectively,and the boron-doped diamond mixed with different boron positions respectively,and calculating the formation energy,cohesive energy,the debye temperature and surface energy characterization of heat resistance index.And through the experimental observation of scanning electron microscopy(SEM),thermogravimetric analysis,XRD analysis and the results of Raman spectroscopy test the calculation results have proved.Within the scope of the concentration of boron,the higher is boron concentration,and the more dispersed is boron atoms,the heat resistance of boron-doped diamond is low.For the boron diamond provides a theoretical basis of heat resistance.This topic mainly launches the research from the following several aspects.Firstly,the crystal structures of boron-doped diamond are imported from"Materials studio" software and inorganic crystal structure database.Ten models of boron-doped diamond C64-xBx(x=0-4)and C61B3-n(n=1-5)have been calculated.Convergence curve tests can determine the k-point cut-off energy,and guarantee the comparison between calculation accuracy.After that,the geometric structure optimization and the cell parameters optimization havebeen calculated.Diamond crystal model after optimization of the crystalstructure have been calculated.when boron concentration increases within a certain amount of boron concentration range,crystal cell volume expanded,and system energy increased,that is,the structure tended to be unstable;When a certain concentration of boron atoms,the more spread out,the greater the volume of the crystal,and doping system energy is higher,the less stable of structure.At the same time,for the study to the surface boron of boron-doped diamond,different models with four different surfaces have been set up respectively:B3C61(100),B3C61(010),B3C61(001),B3C61(111)which concluding 20 surface models.Second,Heat resistance and mechanics are focused on research,through the calculation of elastic modulus,the 10 structures meet the crystal mechanical stability.All the formation energy of BnC64-n(n=0,1,2,3,4)structures and B3C61 structures with different positions are positive.Therefore,these boron-doped diamond compounds can be produced by synthesis only under the condition of high temperature and high pressure.In the forming stage,these compounds will release heat.With the increase of boron concentration and boron-doped diamond crystal structure became weaker.For different boron position of B3C61,the more scattered is boron atoms,the weaker is the boron-doped diamond crystal structure.The calculations of cohesive energy data show that boron diamond crystal structure stability became weaker with the increase of the boron concentration.For different boron position of B3C61,the more scattered is boron atoms,the less stable is the boron-doped diamond crystal structure.Debye temperature values show that Debye temperature value decline gradually and the heat resistance became weak with the increase of the concentration of boron atoms.When replace the center and the compact position of the B atoms of C64 supercell,boron-doped diamond heat resistance is better.Different models with four different surfaces have been calculated respectively:B3C61(100),B3C61(010),B3C61(001),B3C61(111)which concluding 20 surface models.Calculations show that different surface has different heat resistance.Among them,the B3C61(111)is the most unstable and poorest heat resistance of these four surfaces.Finally,the oxidation experiments of boron-doped diamond are done.results by the experiments validate the results of the calculation.Using scanning electron microscopy(sem)observation,when the concentration of boron in diamond is too high,heat resistance and oxidation resistance is reduced.The experimental results conform to the calculation results.Using Raman spectroscopy to analysis structures respectively,the results show boron atoms is in the uneven distribution of diamond single crystal.X-ray diffraction(XRD)analysis showed that ordinary diffraction peaks of the diamond is relatively low,diffraction peak of the(111)surface of the boron-doped diamond is significantly higher.The boron-doped diamond(111)crystal plane is advanced and the most unstable is(111)surface.