| In recent years,with the development of electronic equipment towards high performance,integration and miniaturization,the calorific value per unit area of electronic devices has also increased sharply,so the thermal management of electronic devices has also put forward higher requirements.As a kind of high thermal conductivity material,cubic boron nitride has great application prospect in the preparation of thermal management materials.It also has great potential in the preparation of semiconductor materials.So it has attracted the attention of many researchers.However,the cubic boron nitride prepared in industry inevitably has a variety of lattice defects,and it is difficult to prepare large cubic boron nitride single crystal.The existence of defects will reduce the thermal conductivity of crystals,but the systematic study on the effect of defects on the thermal conductivity is not enough.In this paper,Boltzmann transport equation method and molecular dynamics simulation method were used to study the influence of several common lattice defects on the thermal conductivity of cubic boron nitride.The effects of the concentration of boron isotopes,vacancy,carbon doping and the thermal conductivity of the twin opposite boron nitrate were studied by using the Boltzmann transport equation method,equilibrium molecular dynamics method and non-equilibrium molecular dynamics method respectively.Firstly,the thermal conductivity of cubic boron nitride without defects is calculated by using equilibrium molecular dynamics method and non-equilibrium molecular dynamics method respectively.It is found that the calculation results of the two methods are close to each other and relatively accurate.By fitting the phonon subgroup velocity,it is found that the two methods are related to each other and are consistent in calculating the thermal conductivity.The thermal conductivity of pure 10B cubic boron nitride was calculated by solving Boltzmann transport equation method,equilibrium molecular dynamics method and non-equilibrium molecular dynamics method respectively,which proved that the simulation method was feasible and the potential function was selected properly.It was found that the cubic boron nitride enriched with boron isotopes had higher thermal conductivity than the cubic boron nitride enriched with boron isotopes in the natural state.With the increase of the concentration of boron isotope,the thermal conductivity of cubic boron nitride firstly decreases and then increases,which is roughly symmetric to that of cubic boron nitride with the concentration of 50%.The thermal conductivity of cubic boron nitride decreases sharply due to the vacancy.With the increase of vacancy concentration,the thermal conductivity continues to decrease.The thermal conductivity of the system will decrease sharply if there are few vacancies.With the increase of vacancies,the decrease of thermal conductivity will slow down gradually.The thermal conductivity of cubic boron nitride containing nitrogen vacancy is lower than that of cubic boron nitride with the same number of vacancies.Carbon atom doping is a common doping situation of cubic boron nitride.The carbon atoms in the cubic boron nitride prepared by experiment mainly come from the environment where cubic boron nitride was prepared,and mostly exist on the surface of the crystal.Some carbon atoms are located in the crystal and form bonds with the surrounding atoms.The thermal conductivity of cubic boron nitride decreases with the doping of carbon atom.With the increase of doping atom,the thermal conductivity of cubic boron nitride decreases continuously.With the increase of doping concentration,the decrease of thermal conductivity decreases gradually.The cubic boron nitride with the same carbon content has a higher thermal conductivity than the cubic boron nitride with more nitrogen atoms.Twins can increase the hardness of cubic boron nitride,which is a defect form often observed in the prepared polycrystalline cubic boron nitride.However,the presence of twin boundary has a negative effect on the thermal conductivity of BN cubic.When the thickness of the twin is 5.7nm,the thermal conductivity decreases by 28.45%compared with that of the cubic BN without defects.The thermal conductivity of cubic boron nitride increases linearly with the increase of twin thickness.The presence of twin boundaries decreases the thermal conductivity of cubic BN,so that cubic BN with a smaller twin thickness has a lower thermal conductivity.In summary,isotopes,vacancies,carbon doping and other defects affect the thermal conductivity of cubic BN,thus limiting its application in thermal management.Among them,vacancy and carbon doping have the most dramatic effect on the thermal conductivity of BN.Therefore,the concentration of vacancy and doping should be controlled in the process of experimental preparation to ensure that the material has the required thermal properties. |
