The Heat Transport Behavior Of Nanocrystalline Materials Based On Kapitza Resistance

Due to the special thermoelectric transmission properties,nanocrystalline materials are favored in the field of microelectronic devices and thermoelectric materials.The study found that nanocrystalline materials have many different heat transport properties compared to traditional coarse-grain materials,now it has become a research hotspot.For example,as the grain size reduced to nanoscale,the thermal conductivity of the material changes as the grain size changes.Defects,doping,dislocation etc.can enhance the heat carrier scattering,further reducing the thermal conductivity and deteriorating the heat transport property.Due to the complexity of nanocrystalline materials structure,the research on thermal conductivity is still in its infancy.In order to further studies the heat transport properties of nanocrystalline materials,metal and oxide are studied respectively in this paper.First,the nanocrystalline Ni with grain size of 30-50 nm was prepared by high pressure solid phase sintering of metal powder.Then samples were characterized,including X-ray diffraction,electron microscope scanning,density measurement and thermal diffusivity measurement.It is found that the average grain size increases with the increasing of the sintering temperature.We think that the increasing of thermal gradient will cause the grain boundary to be split and reorganized.In order to study the heat transport of nanocrystalline metals,a two-phase composite model consisting of grain interior regarded as an ordered crystal phase and plastically softer grain boundary affected zone phase was presented.The effects of grain interior and grain boundary affected zone on heat conduction were considered respectively.In this work,we introduce the Kapitcha theory,and study the thermal transport behavior of the carrier through the grain boundary affected zone through the time-independent Schr?dinger wave equation(TISWE)with a pure mathematical model.The thermal conductivity of grain interior was calculated based on a kinetic theory.The whole effective grain thermal conductivity was simulated by a modified formula for composite materials,agreeing well with the experimental results.The results show that as the grain size decreases to 50 nm,it has a strong size effect,and the thermal conductivity decreases as the grain size decreases.