The thermal conductance of interfaces between metals and diamond, which has a comparatively high Debye temperature, is often greater than can be accounted for by twophonon processes. The high pressures achievable in a diamond anvil cell (DAC) can significantly extend the metal phonon density of states to higher frequencies, and can also suppress extrinsic effects by greatly stiffening interface bonding. Here we report time-domain thermoreflectance measurements of metal-diamond interface thermal conductance up to 50 GPa in the DAC for Pb, Au 0.95 Pd 0.05 , Pt and Al films deposited on type 1A natural [100] and type 2A synthetic [110] diamond anvils. In all cases, the thermal conductances increase weakly or saturate to similar values at high pressure. Our results suggest that anharmonic conductance at metal-diamond interfaces is controlled by partial transmission processes, where a diamond phonon that inelastically scatters at the interface absorbs or emits a metal phonon.

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Thermal conductivity of mantle materials controlling the heat balance and thermal evolution of the Earth remains poorly constrained as the available experimental and theoretical techniques are limited in probing minerals under the relevant conditions. We report measurements of thermal conductivity of MgO at high pressure up to 60 GPa and 300 K via diamond anvil cells using the time-domain thermoreflectance technique. These measurements are complemented by model calculations which take into account the effect of temperature and mass disorder of materials within the Earth. Our model calculations agree with the experimental pressure dependencies at 300 and 2000 K for MgO. Furthermore, they predict substantially smaller pressure dependence for mass disordered materials as the mechanism of scattering changes. The calculated thermal conductivity at the core-mantle boundary is smaller than the majority of previous predictions resulting in an estimated total heat flux of 10.4 TW, which is consistent with modern geomodeling estimates.

Analysis of data acquired in time-domain thermoreflectance (TDTR) experiments requires accurate measurements of the thickness of the metal film optical transducer that absorbs energy from the pump optical pulse and provides a temperature dependent reflectivity that is interrogated by the probe optical pulse. This thickness measurement is typically accomplished using picosecond acoustics. The presence of contaminants and native oxides at the interface between the sample and transducer often produce a picosecond acoustics signal that is difficult to interpret. We describe heuristics for addressing this common difficulty in interpreting picosecond acoustic data. The use of these heuristics can reduce the propagation of uncertainties and improve the accuracy of TDTR measurements of thermal transport properties.

Lattice thermal conductivity of ferropericlase and radiative thermal conductivity of iron 18 bearing magnesium silicate perovskite (bridgmanite) -the major mineral of Earth's lower 19 mantle-has been measured at room temperature up to 30 and 46 GPa, respectively, using 20 time domain thermoreflectance and optical spectroscopy techniques in diamond anvil cells. 21 The results provide new constraints for the pressure dependencies of the thermal 22 conductivities of Fe bearing minerals. The lattice thermal conductivity of ferropericlase 23 Mg 0.9 Fe 0.1 O is 5.7(6) W/(m*K) at ambient conditions, which is almost 10 times smaller than 24 that of pure MgO; however, it increases with pressure much faster (6.1(7)%/GPa vs25 3.6(1)%/GPa). The radiative conductivity of Mg 0.94 Fe 0.06 SiO 3 bridgmanite single crystal 26 agrees with previously determined values for powder samples at ambient pressure; it is 27 almost pressure-independent in the investigated pressure range. Our results confirm the 28 reduced radiative conductivity scenario for the Earth's lower mantle, while the assessment 29 of the heat flow through the core-mantle boundary still requires in situ measurements at the 30 relevant pressure-temperature conditions.31