High Pressure Thermal Conductivity LiF Crystal Impact Study

Thermal conductivity of nonmetal crystal at high pressure and high temperature is an important issue in high-pressure physics, geophysics, and material sciences research. According to Debye theory, heat is conducted by phonon diffusion in the insulating dielectric crystal, and thermal diffusion is affected by the phonon anharmonic effect. So the thermal conductivities’research of materials at high temperature and pressure can enhance to understand thermal diffusion and the phonon anharmonic effect. In high-pressure physics research, thermal conductivity measurement is still a difficult problem, and the thermal conductivity measurement technology of dielectric crystal under the condition of extremely high temperature and high pressure is still not mature. The short of high temperature and high pressure thermal conductivity data has become a key factor of restricting or limiting the development of shock wave temperature measurement technology of opacity materials and their complete equation of state (EOS) research. In the geophysics research, composition and state of materials in the earth and planets is significantly affected by the thermal effect, so it is important for applying or developing of earth dynamics model related to heat transmission, understanding thermodynamic evolution and temperature distribution in the core of earth. Therefore, developing and perfecting a high pressure and high temperature thermal conductivity measurement technology has important physical significance and application value for thermal transport properties research, opacity materials shock temperature measurement and geodynamic model development.Based on the research of Ahrens group, we developed and perfected a liquid sandwich thermal conductivity measurement technology. And this method improved the maturity of sandwich thermal conductivity measurement technology by utilizing liquid CHBr3as the sandwich layer and LiF single crystal as the window material. Such as:liquid sandwich method realizes the ideal interface of sample and window by using the liquid property of CHBr3, and then eliminates the interference signal of gap flash, which exists in the sandwich method; liquid sandwich method effectively extends the pressure lower limit of sandwich thermal conductivity measurement technology in present optical pyrometer temperature measurement range by utilizing the nearly blackbody characteristic of shocked CHBr3; liquid sandwich method using LiF single crystal in which shock-induced optical luminescence and extinction is relatively weak as window material simplifies the analysis of thermal radiation signal coming from the interface of sample and window. We developed an in-situ method to determinate the thickness of CHBr3layer by using DPS test technology, and measured the interface thermal relaxation attenuation history by using a time-resolved multi-wavelength pyrometer. Based on the thermal relaxation signal, we carefully analysed the thermal conductivity of shocked LiF single crystal which was determined by thermal relaxation attenuation history, and established an effective data analysis method of absolute high pressure and high temperature thermal conductivity. Using the above data analysis method, three shocked LiF single crystal thermal conductivity data, respectively at-39GPa、-70GPa and-100GPa, were determined by numerical fitting.Applying the measured high pressure and temperature LiF single crystal thermal conductivity data in this paper and the results reported by Holland (Holland K G, et al. Geophysical Monograph.1998,101:335), we studied and discussed the theoretical thermal conductivity model of dielectric crystal. Our results demonstrate that the modified Roufosse theory is good agreement with the experimental data when γιγo=(ρo/ρ)2. And the above result will provide a credible theoretical high pressure and high temperature thermal conductivity model for thermal conductivity correction in shock wave temperature measurement of opacity materials.