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The physics of heat conduction in layered, anisotropic crystals is probed by measurements of the cross-plane elastic constant C 33 and thermal conductivity ⌳ of muscovite mica as a function of hydrostatic pressure. Picosecond interferometry and time-domain thermoreflectance provide high-precision measurements of C 33 and ⌳, respectively, of micron-sized samples within a diamond-anvil cell; ⌳ changes from the anomalously low value of 0.46 W m −1 K −1 at ambient pressure to a value more typical of oxides crystals with large unit cells, 6.6 W m −1 K −1 , at P = 24 GPa. Most of the pressure dependence of ⌳ can be accounted for by the pressure dependence of the cross-plane sound velocities.

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ZnO quantum dots ͑QDs͒ of controlled sizes have been fabricated by a simple sol-gel method. The blueshift of room-temperature photoluminescence measurement from free exciton transition are observed decreasing with the QD size that is ascribed to the quantum confinement effect. From the resonant Raman scattering, the coupling strength between electron and longitudinal optical phonon, deduced from the ratio of the second-to the first-order Raman scattering intensity, diminishes with reducing the ZnO QD diameter. The size dependence of electron-phonon coupling is principally a result of the Fröhlich interaction.

Iron may critically influence the physical properties and thermochemical structures of Earth's lower mantle. Its effects on thermal conductivity, with possible consequences on heat transfer and mantle dynamics, however, remain largely unknown. We measured the lattice thermal conductivity of lower-mantle ferropericlase to 120 GPa using the ultrafast optical pump-probe technique in a diamond anvil cell. The thermal conductivity of ferropericlase with 56% iron significantly drops by a factor of 1.8 across the spin transition around 53 GPa, while that with 8-10% iron increases monotonically with pressure, causing an enhanced iron substitution effect in the low-spin state. Combined with bridgmanite data, modeling of our results provides a self-consistent radial profile of lower-mantle thermal conductivity, which is dominated by pressure, temperature, and iron effects, and shows a twofold increase from top to bottom of the lower mantle. Such increase in thermal conductivity may delay the cooling of the core, while its decrease with iron content may enhance the dynamics of large low shear-wave velocity provinces. Our findings further show that, if hot and strongly enriched in iron, the seismic ultralow velocity zones have exceptionally low conductivity, thus delaying their cooling.

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.

Pressure dependence of thermal conductivity provides a critical test of the validity of the model of the minimum thermal conductivity for describing heat transport by molecular 2 vibrations of an amorphous polymer. We measure the pressure dependence of the thermal conductivity Λ(P) of poly(methyl methacrylate) (PMMA) using a combination of time-domain thermoreflectance and SiC anvil cell techniques. We also determine Λ(P) from a computational model of amorphous polystyrene. In both cases, Λ(P) is accurately predicted by the minimum thermal conductivity model via the pressure dependence of the elastic constants and density.

The Leibfried-Schlömann (LS) equation, a commonly assumed model for the pressure dependence of thermal conductivity , is tested by measurements on compressed H 2 O using a combination of the time-domain thermoreflectance method with the diamond anvil cell technique. The thermal conductivity of ice VII increases by an order of magnitude between 2 and 22 GPa, reaching ≈ 25 W m −1 K −1 . Over a large compression range of ≈4%-33%, the LS equation describes the pressure dependence of of ice VII to better than 20%. 3 With at least 13 polymorphs and the diversity of the hydrogen bond, the behavior of H 2 O under pressure is also a subject of considerable interest in the physics of condensed matter. 4,5 Data on the thermal conductivity of compressed H 2 O are available to a maximum pressure of only 2.4 GPa. 6For dielectrics such as H 2 O ices, oxides, and silicates, thermal conduction is largely controlled by phonon transport. The Leibfried-Schlömann (LS) formula 7,8 is among the most widely used schemes to describe the pressure dependence of . The LS equation is based on a detailed theoretical analysis of phonon transport 8 but it has not been experimentally tested over a range of pressures sufficient to change the Debye frequency, density, and elastic constants of a crystal by large factors. Furthermore, since the LS equation is based on the assumptions that acoustic phonons are the dominant carriers of heat and that the dominant scattering mechanism for acoustic phonons is three-phonon interactions between acoustic modes, its applicability to crystals with multiple atoms per cell has been questioned.9,10 Our previous work 11 showed that the pressure dependence of the cross-plane thermal conductivity of layered muscovite crystal could be adequately described by the LS equation when we assumed that the effective value of the Debye frequency varies as the square root of the cross-plane elastic constant C 33 . Muscovite is highly anisotropic, however, and the applicability of the LS equation in this case is not strictly valid.This study aims to measure the thermal conductivity of H 2 O over a pressure range that was not accessible previously. The data on ice VII, a cubic crystal with a relatively small bulk modulus, allow us to test the LS equation over a large compression ratio. Our method combines the time-domain thermoreflectance (TDTR) method 12 in a diamond anvil cell (DAC) with density functional theory (DFT) calculations of the vibrational density of states (DOS). At room temperature, cubic ice VII (space group P n3m) is stable between 2.1 and ≈60 GPa. 13,14 With its extrapolated zero pressure bulk modulus K 0 = 21.1 ± 0.5 GPa and the pressure derivative K 0 = 4.4 ± 0.1, 15 ice VII is compressed by more than 30% at 22 GPa.Symmetric DACs with 600-μm-culet diamonds and steel gasket were used to compress distilled H 2 O to 22 GPa. Pressure was determined from ruby fluorescence. 16 An 80-nm-thick Al film, coated on a 20-μm-thick sheet of muscovite mica [KAl 2 (Si 3 Al)O 10 (OH) 2 , grade V-1 from SPI Supplies], was lo...