Abstract
Sodium chloride (NaCl) is an important, commonly used pressure medium and pressure calibrant in diamond-anvil cell (DAC) experiments. Its thermal conductivity at high pressure–temperature (P–T) conditions is a critical parameter to model heat conduction and temperature distribution within an NaCl-loaded DAC. Here we couple ultrafast optical pump-probe methods with the DAC to study thermal conductivity and compressional velocity of NaCl in B1 and B2 phase to 66 GPa at room temperature. Using an externally-heated DAC, we further show that thermal conductivity of NaCl-B1 phase follows a typical T−1 dependence. The high P–T thermal conductivity of NaCl enables us to confirm the validity of Leibfried-Schlömann equation, a commonly used model for the P–T dependence of thermal conductivity, over a large compression range (~ 35% volume compression in NaCl-B1 phase, followed by ~ 20% compression in the polymorphic B2 phase). The compressional velocities of NaCl-B1 and B2 phase both scale approximately linearly with density, indicating the applicability of Birch’s law to NaCl within the density range we study. Our findings offer critical insights into the dominant physical mechanism of phonon transport in NaCl, as well as important data that significantly enhance the accuracy of modeling the spatiotemporal evolution of temperature within an NaCl-loaded DAC.
Highlights
Sodium chloride (NaCl) is an important, commonly used pressure medium and pressure calibrant in diamond-anvil cell (DAC) experiments
By performing additional simultaneous high P–T thermal conductivity measurements, we further show that the thermal conductivity of NaCl at high pressures scales with the T−1 dependence, typical of a pure crystal
Using the combination of ultrafast time-domain thermoreflectance, picosecond interferometry, and DAC techniques, we have precisely determined the values of thermal conductivity and compressional velocity of NaCl, a common, important pressure medium for DAC experiments, to 66 GPa
Summary
Sodium chloride (NaCl) is an important, commonly used pressure medium and pressure calibrant in diamond-anvil cell (DAC) experiments. Recent advances in the combination of time-resolved optical techniques with a diamond-anvil cell (DAC)[8,10,11] have enabled better determination of materials’ thermal conductivity under extreme conditions In these measurements, the thermal conductivity of a sample of interest within the DAC is typically derived by comparing experimental data related to the heat diffusion rate through the sample with numerical calculations by a thermal model where the thermal conductivity of the pressure transmitting medium is one of the key parameters. Though recently McGuire et al.[32] reported relative changes in NaCl’s thermal conductivity as a function of relative density across the B1–B2 transition, a precise determination of the thermal conductivity values at high P–T conditions remains unavailable Lack of such critical data may lead to inaccurate modeling of the temperature evolution in laser-heated or externallyheated DAC experiments, which in turn could give rise to inaccurate thermal conductivity of the sample of interest. In addition to identifying that the anharmonic three phonon scattering plays a key role in heat transfer in NaCl crystal, our results here significantly improve the modeling of heat transfer and enhance the accuracy of thermal conductivity measurements under high P–T conditions
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