氮化硼热导率的分子动力学模拟

发布时间：2018-01-25 04:16

本文关键词： 分子动力学热导率单层氮化硼多层氮化硼　出处：《东南大学》2015年硕士论文　论文类型：学位论文

【摘要】：氮化硼与石墨烯有着相似的晶格结构,具有独特的物理和化学性能,是一种优良的热学材料。虽然氮化硼的热导率低于石墨烯,但是却远远高于其他金属和非金属材料,由氮化硼与石墨烯相结合的热电器件受到了越来越广泛的关注。本文采用非平衡态分子动力学模拟计算了单层和多层氮化硼(BN)的热导率。单层氮化硼(SLBN)的热导率受到自身结构和多种外在因素的影响。氮化硼纳米带具有锯齿型(Z-BNNRs)和扶手椅型(A-BNNRs)两种手性,声子在前者的传播速度高于后者导致前者的热导率高于后者将近20%。受到边界散射的影响,氮化硼纳米带(BNNRs)的热导率大大低于氮化硼薄膜(h-BN)的热导率。随着温度的升高,氮化硼内部的声子群速度降低,热导率也逐渐减小。同位素掺杂的氮化硼薄膜随着掺杂浓度的增加,热导率先是减小然后增加,在掺杂浓度为50%时,热导率达到最小。随着温度的增加,不同掺杂浓度的热导率越来越接近,这是由于高温时高频声子数目增加使得声子U散射更为显著,超过了杂质散射对热导率的影响。带有晶格缺陷的氮化硼薄膜的热导率大大地降低,并且随着缺陷浓度的增加,热导率不断减小,在空穴浓度到达一定的比例后,温度对氮化硼薄膜热导率的影响几乎可以忽略不计,说明晶格缺陷引起的热导率的变化超过了温度对热导率的影响。氮化硼薄膜热导率随着热流方向尺寸的增加逐渐增大并逐渐趋于收敛,在常温下单层氮化硼薄膜面向热导率高达606Wm-1K-1。多层氮化硼(MLBN)是由单层氮化硼(SLBN)通过层间的范德华力(van der Waals forces)堆叠在一起的,其面向热导率相对于单层氮化硼并没有明显变化,当层间的相互作用力增强时,多层氮化硼的热导率下降；氮化硼的法向热导率随着层数的增加逐渐增加,其界面热阻在层数较少时不能忽略,随着层数的增加,其界面热阻值不断减小直至收敛；多层氮化硼/石墨烯堆叠结构的热导率在石墨烯和氮化硼热导率的平均值以下,说明了层间作用力起到了减小热导率的作用；氮化硼/石墨烯的超晶格结构,其法向热导率随着晶格周期长度的增加先减小后增加。其变化趋势符合波动模式的结论。
[Abstract]:Boron nitride and graphene have similar lattice structure, unique physical and chemical properties, and are an excellent thermal material, although the thermal conductivity of boron nitride is lower than that of graphene. But it is much higher than other metals and nonmetallic materials. Thermoelectric devices combined with boron nitride and graphene have attracted more and more attention. In this paper, the thermal conductivities of monolayer and multilayer boron nitride (BN) have been calculated by non-equilibrium molecular dynamics simulation. The thermal conductivity of SLBN is affected by its own structure and many external factors. Boron nitride nanobelts have two chiral properties: zigzag Z-BNNRsand armchair A-BNNRs. The propagating velocity of phonon in the former is higher than that in the latter, and the thermal conductivity of the former is higher than that of the latter by nearly 20 percent, which is affected by the boundary scattering. The thermal conductivity of BNNRs is much lower than that of boron nitride film h-BN. With the increase of temperature, the phonon group velocity in boron nitride decreases. The thermal conductivity of isotopic doped boron nitride films decreases first and then increases with the increase of doping concentration. The thermal conductivity reaches the minimum with the increase of temperature when the doping concentration is 50. The thermal conductivity of different doping concentrations is closer and closer, which is due to the increase in the number of high-frequency phonons at high temperature, which makes the phonon U scattering more significant. The thermal conductivity of boron nitride thin films with lattice defects is greatly reduced, and the thermal conductivity decreases with the increase of defect concentration. The effect of temperature on the thermal conductivity of boron nitride films can be neglected when the hole concentration reaches a certain ratio. The results show that the change of thermal conductivity caused by lattice defects exceeds the effect of temperature on thermal conductivity. The thermal conductivity of boron nitride film increases with the increase of the dimension of heat flux and tends to converge gradually. At room temperature, the thermal conductivity of single layer boron nitride film is up to 606Wm-1K-1.The multilayer boron nitride (MLBN) is made by single layer boron nitride (SLBN) through the van der Waals force between the layers. Van der Waals force. The thermal conductivity of multilayer boron nitride decreases when the interlaminar interaction is enhanced. The thermal conductivity of multilayer boron nitride is not significantly different from that of monolayer boron nitride. The normal thermal conductivity of boron nitride increases gradually with the increase of the number of layers, and the interfacial thermal resistance can not be ignored when the number of layers is small. With the increase of the number of layers, the interfacial thermal resistance decreases continuously until convergence. The thermal conductivity of the multilayer boron nitride / graphene stack structure is below the average of the thermal conductivity of graphene and boron nitride, which indicates that the interlaminar force plays a role in reducing the thermal conductivity. The normal thermal conductivity of the superlattice structure of boron nitride / graphene decreases firstly and then increases with the increase of lattice cycle length.
【学位授予单位】：东南大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TQ128

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