Heat transport behavior of bicrystal ZnO containing tilt grain boundary

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As a new graphene-based two-dimensional semiconductor material, C3N has attracted extensive attention from researchers due to its excellent mechanical and electronic properties.Whether there are differences in the phonon transport mechanism of different C3N structures remains to be further investigated.Therefore,four kinds of C3N with different patterns were constructed in this paper, and their thermal conduction mechanism was studied by the non-equilibrium molecular dynamics (NEMD) method. The research results show that:(1) Among the four patterns,the C3N (M3) with the perfect structure has the highest thermal conductivity,followed by M1,and the lowest thermal conductivity of M4.(2) Moreover,the thermal conductivity of C3N with different patterns has obvious size and temperature effects.When the sample length is short,the phonon transport is mainly ballistic transport,while diffusion transport dominates the heat transport when the sample length is further increased.As the temperature increases,Umklapp scattering dominates the heat transport,making the thermal conductivity and temperature show a 1/T trend.(3) Compared with the M3,the patterns of M1 and M4 have larger phonon band gaps,and their dispersion curves are further softened.At the same time,regardless of low-frequency or high-frequency phonons,localized features appear in t M1 and M4(especially the M4),which has a significant inhibitory effect on thermal conductivity.This paper provides an idea for better design of thermal management materials.

Section: 尺寸效应和温度效应unclassified

Thermal conduction mechanism of graphene-like carbon nitride structure (C3N)

Kai-Bo¹,

Ren²,

Yong-Jia³

et al. 2023

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Thermal conductivities of different period Si/Ge superlattices

华北电力大学¹

2021

Thermoelectric materials, which can convert wasted heat into electricity, have attracted considerable attention because they provide a solution to energy problems. The Si/Ge superlattices have shown tremendous promise as effective thermoelectric materials. The period lengths of the Si/Ge superlattices can effectively tailor the phonon's transport behaviors and control their thermal conductivities. In this paper, three kinds of Si/Ge superlattices with different period length distributions (uniform, gradient, random) are constructed. The non-equilibrium molecular dynamics (NEMD) method is used to calculate the thermal conductivities of Si/Ge superlattices under the different period length distributions. The effect of the sample’s total length and temperature on the superlattice's thermal conductivity are studied. The simulation result shows that the thermal conductivity of gradient and random periodical Si/Ge superlattices are significantly reduced at room temperature compared with that of the uniform period Si/Ge superlattices. Phonons are transported by wave or particle properties in the different periodical superlattices. The thermal conductivity of uniform period superlattices has an obvious size effect with the increasing of the sample total length. In contrast, the thermal conductivity of gradient, random periodical Si/Ge superlattices are weakly dependent on the sample’s total length. At the same time, temperature is an important factor affecting the heat transport properties. We find that the temperature affects the thermal conductivities of the three kinds of superlattices in different ways. With the increase of the temperature, (i) the thermal conductivity of uniform periodical superlattices shows an obvious temperature effect; (ii) the thermal conductivity of the gradient and random periodical Si/Ge superlattices are nearly unchanged due to the competition between phonon localization weakness and phonon-phonon scattering enhancement. In addition, the phonon densities of states of superlattices with three different periodical length distributions are calculated. We find that in the picture of uniform periodical Si/Ge superlattices, the number of pronounced peaks quickly decreases as the period length increases, particularly at higher frequencies. This indicates that as the period length increases, fewer coherent phonons will be formed over the superlattices. Moreover, the scattering mechanisms of phonons for gradient and random periodical Si/Ge superlattices are basically the same at 100 K and 500 K. These findings provide a developmental way to further reduce the thermal conductivity of superlattices.

Thermal conductivity of Si/Ge superlattices containing tilted interface

Liu¹,

Ren²,

Hao³

et al. 2021

The non-equilibrium molecular dynamics (NEMD) method is used to study the thermal conductivities of Si/Ge superlattices with tilted interface under different period lengths, different sample lengths, and different temperatures. The simulation results are as follows. The thermal conductivity of Si/Ge superlattices varies nonmonotonically with the increase of interface angle: when the period length is 4–8 atomic layers, the thermal conductivity for the interface angle of 45° is one order of magnitude larger than those for other interface angles, and the thermal conductivity increases linearly with the sample length increasing and decreases with the temperature increasing. However, when the period length is 20 atomic layers, the thermal conductivity is weakly dependent on sample length and temperature due to the existence of phonon localization.