The presence of water in minerals generally alters their physical properties. Ringwoodite is the most abundant phase in the lowermost mantle transition zone and can host up to 1.5–2 wt% water. We studied high‐pressure lattice thermal conductivity of dry and hydrous ringwoodite by combining diamond‐anvil cell experiments with ultrafast optics. The incorporation of 1.73 wt% water substantially reduces the ringwoodite thermal conductivity by more than 40% at mantle transition zone pressures. We further parameterized the ringwoodite thermal conductivity as a function of pressure and water content to explore the large‐scale consequences of a reduced thermal conductivity on a slab's thermal evolution. Using a simple 1‐D heat diffusion model, we showed that the presence of hydrous ringwoodite in the slab significantly delays decomposition of dense hydrous magnesium silicates, enabling them to reach the lower mantle. Our results impact the potential route and balance of water cycle in the lower mantle.

Seismic anomalies observed in Earth's deep mantle are conventionally considered to be associated with thermal and compositional anomalies, and possibly partial melt of major lower‐mantle phases. However, through deep water cycle, impacts of hydrous minerals on geophysical observables and on the deep mantle thermal state and geodynamics remain poorly understood. Here we precisely measured thermal conductivity of δ‐(Al,Fe)OOH, an important water‐carrying mineral in Earth's deep interior, to lowermost mantle pressures at room temperature. The thermal conductivity varies drastically by twofold to threefold across the spin transition of iron, resulting in an exceptionally low thermal conductivity at the lowermost mantle conditions. As δ‐(Al,Fe)OOH is transported to the lowermost mantle, its exceptionally low thermal conductivity may serve as a local thermal insulator, promoting high‐temperature anomalies and the formation of partial melt and thermal plumes at the base of the mantle, strongly influencing thermo‐chemical profiles in the region and fate of Earth's deep water cycle.

No abstract

Siderite was proposed to be an important mantle carbon‐hosting mineral in Earth's deep carbon cycle. It undergoes a pressure‐induced spin transition of iron around 40–55 GPa, through which many physical properties change drastically. Thermal conductivity of mantle minerals is key to control temperature profiles and thermal evolution in the mantle and subducting slabs. However, the lattice thermal conductivity of iron‐bearing carbonates under relevant mantle conditions has never been investigated. Here we combined high‐pressure diamond‐anvil cell, Raman spectroscopy, and ultrafast optical pump‐probe method to measure the lattice thermal conductivity of siderite to 67 GPa at room temperature. We found that during the spin transition the thermal conductivity varies significantly with the extent of low‐spin state, which is largely different from that of the lower‐mantle ferropericlase. Our results further suggest that when the siderite is transported to depths of 1,400–1,800 km, such thermal conductivity anomaly within a narrow pressure range may induce anomalies in local thermochemical profiles and alter the distribution fields of subducting minerals, which in turn would influence the fate of carbonates in global carbon cycle.

Highly transparent zinc oxide (ZnO)-based thin-film transistors (TFTs) with gold nanoparticles (AuNPs) capable of detecting visible light were fabricated through spray pyrolysis on a fluorine-doped tin oxide substrate. The spray-deposited channel layer of ZnO had a thickness of approximately 15 nm, and the thickness exhibited a linear increase with an increasing number of sprays. Furthermore, the ZnO thin-film exhibited a markedly smoother channel layer with a significantly lower surface roughness of 1.84 nm when the substrate was 20 cm from the spray nozzle compared with when it was 10 cm away. Finally, a ZnO and Au-NP heterojunction nanohybrid structure using plasmonic energy detection as an electrical signal, constitutes an ideal combination for a visible-light photodetector. The ZnO-based TFTs convert localized surface plasmon energy into an electrical signal, thereby extending the wide band-gap of materials used for photodetectors to achieve visible-light wavelength detection. The photo-transistors demonstrate an elevated on-current with an increase of the AuNP density in the concentration of 1.26, 12.6, and 126 pM and reach values of 3.75, 5.18, and 9.79 × 10−7 A with applied gate and drain voltages. Moreover, the threshold voltage (Vth) also drifts to negative values as the AuNP density increases.

No abstract

Ice-VII is a high-pressure polymorph of H2O ice and an important mineral widely present in many planetary environments, such as in the interiors of large icy planetary bodies, within some cold subducted slabs, and in diamonds of deep origin as mineral inclusions.However, its stability at high pressures and high temperatures and thermoelastic properties are still under debate. In this study, we synthesized ice-VII single crystals in externallyheated diamond anvil cells and conducted single-crystal X-ray diffraction experiments up to 78 GPa and 1000 K to revisit the high-pressure and high-temperature phase stability and thermoelastic properties of ice-VII. No obvious unit-cell volume discontinuity or strain anomaly of the high-pressure ice was observed up to the highest achieved pressures and temperatures. The volume-pressure-temperature data were fit to a high-temperature Birch-Murnaghan equation of state formalism, yielding bulk modulus KT0 = 21.0(4) GPa, its first pressure derivative KT0ʹ = 4.45(6), dK/dT = -0.009(4) GPa/K, and thermal expansion relation aT = 15(5)´10 -5 +15(8)´10 -8 ´(T-300) K -1 . The determined phase stability and thermoelastic properties of ice-VII can be used to model the inner structure of icy cosmic bodies. Combined with the thermoelastic properties of diamonds, we can reconstruct the isomeke P-T paths of ice-VII inclusions in diamond from depth, offering clues on the water-rich regions in Earth's deep mantle and the formation environments of those diamonds.