| Diamond is the hardest material in nature and has excellent thermal conductivity.Studies have shown that there are defects such as grain boundaries in its microstructure.The existence of the interface will affect the heat transfer efficiency of the material at the nanometer scale.For the thermal conductivity of the material,a large number of grain boundaries will not only affect the heat transfer between the grains,but also affect the heat transfer inside the grain.In this paper,the thermal conductivity of diamond twin boundaries is studied by computer simulation.The thermal conductivity of different types of twin boundaries was calculated by non-equilibrium molecular dynamics method.It is found that the thermal conductivity of the(111)twin boundary in diamond is the largest,which is 45.45GW/m~2K.In order to understand more deeply the phonon propagation at different types of interfaces,the time domain orthogonal analysis is performed to calculate the average group velocity of phonons and the mean free path of phonons.The results are obtained in(111).The structural direction of the twin boundary,the mean free path of the phonon and the average group velocity of the phonon are 0.29?and 13.36?/ps,respectively,which are much larger than the phonon free path and group velocity of the(310)twin boundary.After calculating the thermal conductivity of twin grain boundaries by molecular dynamics,we simulate the wave packets passing through the twin grain boundaries at different frequencies and k-point phonons by lattice dynamics method.It is clear from the simulation results that different kinds of diamond twin boundaries have different transmission ability to the wave packet.Combining with the calculation results of molecular dynamics,we can see that the transmission coefficient of LA acoustic branch is relatively high at the twin boundaries with high thermal conductivity.For example,the structure containing(111)twin boundaries,the transmission coefficient of long acoustic branch is basically above 95%,as a comparison,at the same time,we can see that the transmission coefficient of LA acoustic branch is higher than that of(111)twin boundaries.In this paper,the transmission of phonon wave packet on TA acoustical branch in the(111)twin structure is also analyzed.Since the temperature of Debye of diamond is very high,and the thermal conductivity of molecular dynamics calculation is carried out within the scope of classical theory,at the end of the article,we quantify the calculated thermal conductivity of the interface and correlate it by velocity.The function obtains the state density projection of the phonon.After considering the temperature effect,the value of the interface thermal conductivity at 300K is calculated.It can be seen that the influence of temperature on the thermal conductivity of the twin boundary is very important. |
