Theoretical Study On Thermoelectric Properties And Regulation Of Carbon-Based Nanotubes

With the acceleration of industrialization,energy shortages and environmental pollution have become increasingly prominent.In addition,the existing energy utilization rate is low,and most of it is dissipated in the form of thermal energy,resulting in a huge waste of energy.A reliable way to solve these problems is to use thermoelectric materials.Thermoelectric materials convert thermal energy and electrical energy to each other to ensure the recycling of energy.The devices made of thermoelectric materials have many advantages,such as no pollution,safe and reliability,long service life,etc.,which have attracted extensive attention of researchers.Studies have shown that compared with traditional bulk materials,low-dimensional nanomaterials have more excellent thermoelectric properties.At the same time,due to the continuous improvement of experimental technology,many types of carbon-based nanotubes?single-wall,multi-wall carbon nanotubes,etc.?have been successfully prepared.Therefore,studying the thermoelectric properties of these carbon-based nanotube materials can not only provide theoretical guidance for designing and preparing effective thermoelectric materials,but also provide solutions for alleviating global environmental problems.Based on the non-equilibrium Green function method,this paper comprehensively analyzes the effect of graphene nanosprings on the thermoelectric properties of carbon nanotubes,and explores the thermoelectric properties of perfect C₂N nanotubes.It provides a theoretical model for the development of thermoelectric devices based on carbon nanotubes.The foremost investigations of the article are as follows:1.Using the non-equilibrium Green's function method,we compared the influence of armchair and zigzag graphene nanosprings on the ballistic thermoelectric transport of carbon nanotubes.The calculation results show that by introducing graphene nanosprings,the thermoelectric figure of merit of carbon nanotubes is significantly improved.At 700K,the ZT value is about ten times that of the original carbon nanotubes.Such enhancement is mainly due to the obvious suppression of phonon and electronic thermal conductance and the increase of Seebeck coefficient.In addition,compared to the zigzag graphene nanospring,the introduction of the armchair case has better thermoelectric properties.This shows that nanosprings are indeed an effective way to improve the thermoelectric properties of carbon nanotubes,and provide a favorable theoretical basis for obtaining more efficient thermoelectric materials.2.We use non-equilibrium Green's function method to study the thermoelectric properties of perfect C₂N nanotubes with different tube diameters and types.We found that the phonon and electron transmission of the armchair and zigzag C₂N nanotubes both show obvious quantum steps,and increase significantly with the increase of the tube diameter.It can be understood that the nanotubes with large tube diameters provide more channels for phonon and electron transport.Because of the anisotropy,the ZT value of the armchair and the zigzag C₂N nanotubes is different with the change of tube diameter,and the value of armchair nanotubes is larger than zigzag case.In addition,due to lower thermal conductance and higher Seebeck coefficient,C₂N nanotubes have better thermoelectric properties than carbon nanotubes.This shows that C₂N nanotubes?especially armchair case?have greater potential in carbon-based thermoelectric materials.