Modulating Heat Conduction Of Ferroelectric Materials With Electric Field And The Mechanism Study

Realizing the dynamic modulation of thermal conductivity of materials has important significance in promoting the development of electronics,aerospace,building energy conservation and other fields.In this thesis,based on the unique response of the microstructure of ferroelectric materials to the electric field,combined with the nanoscale heat conduction theory,the scientific issue of modulating thermal conductivity of ferroelectric materials with electric field and the internal mechanismis studied.Firstly,the strategy to modulate the thermal conductivity of organic ferroelectric:poly（vinylidene fluoride）（PVDF）by electric polarization is proposed.With molecular dynamics simulation,it is found that the thermal conductivity change range of PVDF crystal at room temperature is 0.16～0.52 W·m^-1k^-1,and the change ratio is 3.25.The modulation effect gradually weakens with the increase of temperature.Experimentally,the thermal conductivity change ratio of semi-crystalline film is 1.53,which further verifies this strategy.The analysis of morphology and phonon properties shows that the enhanced arrangement order and interaction between polymer chains suppress phonon scattering,increase phonon group velocity,and result in enhanced thermal conductivity after polarization.Compared with the method of doping high thermal conductivity fillers,modulating with electric field has smaller effect on the mechanical properties of materials.Secondly,the effect of electric polarization on the thermal conductivity of hydrogen-bonded ferroelectrics:odd-numbered nylons is investigated.Simulations show that the hydrogen bond density in odd-numbered nylon increases after polarization,and the thermal conductivity can be improved from 0.3 to 0.9 W·m^-1k^-1.The thermal conductivity change ratio increases with the increase of the amide group’s density.Further analyses of hydrogen bond,morphology,and phonon property show that the increased interchain hydrogen bond density provides more efficient thermal conduction paths,improves the structural order,and facilitates the transport of phonons.Moreover,the thermal conductivities of unpoled structure under different electric fields show that thermal conductivity can be effectively changed only when the electric field exceeds the threshold value.Thirdly,the modulation of thermal conductivity of inorganic ferroelectric:barium titanate crystal by electric field is studied.Using molecular dynamics simulations,it is found that the electric field can switch the polarization direction of the barium titanate crystal,causing 1%～2%change in its lattice size.The structural anisotropy leads to the anisotropy of its thermal conductivity.Under the electric field of 30 MV/m,the thermal conductivity regulation ratio of 1.83(2.82～5.26 W·m^-1K^-1)can be achieved by changing the direction of the electric field.Maintaining an electric field of 300 MV/m can increase the modulation ratio to 2.26.The analysis of phonon properties shows that the change of thermal conductivity mainly comes from the change of low frequency phonon scattering degree.Finally,the effect of the electric field on the thermal conductance of the inorganic/organic（Si/PVDF）interface is investigated.The molecular dynamic simulation results show that the interfacial thermal conductance can be increased from 50.6MW·m^-2K^-1 to 107.3 MW·m^-2K^-1 with the enhancement of the applied electric field.Moreover,the interfacial thermal conductance is also affected by the direction of the electric field.The analysis of atomic density distribution and interface bonding strength shows that the enhancement of van der Waals interaction induced by electric field is responsible for the increase of interfacial thermal conductance.Moreover,changing the direction of electric field can change the type of atoms close to the interface,thereby affecting the interface bonding strength and changing the interface thermal conductance.In this thesis,the response of thermal conductivity of different types of ferroelectric materials to electric field and its mechanism are studied,which provides insights and guidance for dynamic control of thermal conductivity by using external field.