The Asymmetric Heat Conduction In One Dimensional Nonlinear Lattices And The Native Vacancy Defects In Bismuth Sulfide

Since the heat conduction in one dimensional system is different from themacroscopic thermal transport properties in three dimensional system, people try toexpound the macroscopic phenomenon of heat conduction in the sight of microscopicdynamics mechanism. Although there still lacks a comprehensive theory about theheat conduction in low dimensional system, some intriguing findings have establishedthe foundation for the Phononics, such as the thermal rectification effect, negativedifferential thermal resistance, etc. These indicate that the phonons in the form of heatcan be controlled and manipulated analogous to the electrons in heterogeneoussemiconductor junction. Therefore, the design and preparation of phonon devices withdifferent functions have become the research hotspot of the thermal transportproperties of low-dimensional system in recent years.By using nonequilibrium molecular dynamics simulations, the present paperstudied the asymmetric heat conduction in two kinds of one dimensional nonlinearlattices which are the composite system consisting of FK and FPU lattices and thehomogeneous FK lattices with linear mass gradient. The aim is to study the influenceof interfacial coupling strengthand the system size on the system. Thecalculated results show that when an interfacial spring is introduced to the twosystems, the thermal rectification is reversed when the temperature bias of the heatbaths is greater than a certain value. Intuitively, the negative differential thermalresistance existing at the interface leads to the rectification reversal. Therefore, theexistence of interfacial spring gives rise to the rectification reversal essentially. Inaddition, there are two types of asymmetric heat conduction before and after therectification reversal. The rectification reversal is closely related to the systemparameters. Only with specific interfacial coupling strength and system size, can therectification reversal appear. Considering the novel asymmetric heat conduction in thesystem, it may possess possible applications to manage the thermal rectification insitu directionally only by adjusting the thermal bias without re-building the structure.Semiconductor photocatalyst material is a new type of energy material. With adirect band gap between1.2-1.7eV, bismuth sulfide which is environmentally friendlyand with high photoelectric conversion efficiency has become the research hotspot inthe field of photoelectric, thermoelectricity and sensors. Since the native vacancies defects are relatively common during the preparation of samples, it is important tostudy the effect of native defects on the material properties. The present paper studiedthe influence of native vacancies defects of Bi2S3on its electronic properties andphotocatalytic absorption by using first-principles density functional theory. Thecalculated results show that the inequal vacancies will cause different changes of theband gap of Bi2S3. Moreover, there exists an intermediate level in the band structureof Bi2S3-VS, which provides a separation centre for the electron hole pair, therebyreducing their recombination rate. The formation energy of S vacancy is much smallerthan that of Bi vacancy, indicating that the existence of S vacancy in Bi2S3is easierthan the Bi vacancy during the preparation process. The results illustrate that thenative defects are the most likely physical cause for the scattered band gaps obtainedby experiments.