Vitali B. Prakapenka

The melting temperature and electrical resistivity of iron at high pressure are essential for understanding Earth’s core. Here we use a new high-pressure method – microsecond pulsed Joule heating in diamond anvil cells – to identify melting and measure resistivity of solid and liquid iron. More than 300 reproducible melting measurements indicate a surprisingly shallow melting curve, reaching 6 K/GPa and 4160 ± 80 K at 200 GPa. Extrapolating in pressure and iron alloy composition, and combining with our 76 μ Ω cm measurement of liquid iron’s resistivity, we infer a relatively cold core-mantle boundary (3430 K) with a low adiabatic outer core heat flow (9.8 TW). This suggests thermal convection alone could have powered the geodynamo prior to inner core formation and that today’s lowermost mantle is fully solid.

Planetary interiors cool and evolve over geologic time, and their thermal evolution depends on heat transport through their constituent layers. Here, the thermal conductivity of iron has been measured between 19 and 65 GPa and between 1700 and 2500 K in order to constrain its value at the conditions of small planetary cores. Our results are comparable to the low end of electrical resistivity experiments on fcc‐Fe at comparable conditions, suggesting that the relationship between electrical and thermal conductivity described by the Wiedemann‐Franz law provides a reasonable description of heat transport in fcc‐Fe at planetary core conditions. The thermal conductivity of fcc‐Fe at high pressures and temperatures places an upper bound on the thermal conductivity of Mercury's core, with a value of 52(7) W/m/K at 40 GPa, which corresponds to the pressure at the center of the core. Accounting for the effects of silicon and sulfur alloying reduces Mercury's core conductivity by 10%–40% for realistic core compositions, which satisfy constraints on Mercury's core density.

H ₂ CO ₃ - Pnma is a low temperature carbonic acid polymorph, which can occur at the same pressure (∼9 GPa) than the high-temperature phase H ₂ CO ₃ - P 2 ₁ / n . The crystal structure of H ₂ CO ₃ - Pnma was refined from synchrotron single crystal diffraction data.

Subducted potassium feldspar transforms into a hollandite-type structure, rendering it a plausible carrier for large lithophile elements and volatiles, possibly including molecular water, into the deep mantle. Nevertheless, the capacity of this phase to incorporate and retain such incompatible species under deeper mantle conditions has remained largely unconstrained. We report here the formation of the hydrated hollandite-type structures from subducting K-bearing feldspars in the presence of H ₂ O near 400 km depth conditions. Combined in situ high-pressure and -temperature synchrotron X-ray diffraction and ex situ synchrotron Fourier-transform infrared spectroscopy reveal molecular H ₂ O incorporated within the expanded 1D tunnels together with hydroxyls through the aluminosilicate octahedral framework of the hollandite-type structure, yielding up to net ~1.97 wt.% water content. Subsequently, dehydration occurs via framework distortion upon exceeding the lower boundary of the mantle transition zone near 720 to 780 km. We estimate that, over a 200 Ma of subduction cycle, hydrated hollandite-type phases may have contributed the water flux to the topmost lower mantle by the amount to suppress the formation of the representative lower mantle phase, bridgmanite. This process may thus be linked to the apparent depression of 660-km discontinuity in penetrating slabs and their surrounding regions to address key limitations of existing akimotoite- and basalt-derived models.

Pentazolates, an emerging family of nitrogen-rich materials featuring the aromatic cyclo-N5– anion, typically crystallize as nonpolymeric or three-dimensional (3D) coordination networks, whereas low-dimensional (1D and 2D) forms remain exceptionally rare. Here, we exploit the square-planar coordination preference of d8 Pd2+ to achieve dimensional control and synthesize Pd(N5)2·N2, the first high-pressure 1D pentazolate coordination polymer. The compound forms in a laser-heated diamond anvil cell at 118 GPa and 2900 K, while lower-pressure experiments yield only PdN2 dinitride. The crystal structure of Pd(N5)2·N2 was determined by synchrotron single-crystal X-ray diffraction from a multigrain sample and corroborated by density functional theory calculations. This discovery establishes a strategy for engineering low-dimensional pentazolate-based materials and potentially enabling dimensional control in other polynitrides. We also provide an overview of experimentally synthesized high-pressure pentazolates and discuss how cation properties influence their synthesis pressures, thereby improving understanding of pentazolate formation pressures.

Nuclear resonant scattering (NRS) provides the basis for powerful synchrotron-based techniques, including synchrotron Mössbauer spectroscopy (SMS) and nuclear resonant inelastic x-ray scattering (NRIXS), which probe the elastic, magnetic, thermodynamic, and vibrational properties of iron-bearing materials and are, therefore, well suited for studying the structure and composition of Earth’s and planetary interiors. Here, we report the development and commissioning of a double-sided laser heating system for diamond anvil cell experiments at the 3-ID beamline of the Advanced Photon Source (APS). A key feature of the system is a 7° offset between the x-ray and laser-delivery paths, which positions the near-sample mirrors outside the x-ray path. This design minimizes x-ray absorption, enhances the NRS signal rate during laser heating, improves imaging quality, and significantly reduces thermal drift during extended data acquisition periods. The setup is optimized to match the reduced x-ray beam size available after the APS upgrade, making NRS measurements under extreme pressure–temperature conditions more practical. In addition, the system supports complementary online ruby fluorescence and x-ray diffraction measurements for characterizing samples before and after laser heating. We demonstrate the performance of the system through representative SMS and NRIXS measurements conducted under simultaneous high-pressure and high-temperature conditions.

We report the synthesis of a calcium-intercalated boron–carbon framework with the “NPO” zeolite topology. Hexagonal CaB3C3 crystallizes in space group P62m (No. 189), under high-pressure, high-temperature conditions, in a structure predicted for hypothetical metastable carbon allotropes. The structure, which exhibits minimal or no substitutional framework disorder, is comprised of four-coordinated B/C atoms that form channels along the crystallographic Z-axis, trapping calcium ions. Calculations based on density functional theory (DFT) indicate that hexagonal CaB3C3 is thermodynamically stable above 30 GPa, and theoretical/experimental results suggest that the recoverable compound exhibits a superconducting transition near 5 K at ambient pressure. The formation of hexagonal CaB3C3 further expands the range of synthesizable structural topologies for carbon-based tetrahedral nets with versatile physical properties.

Determining the solidus of Fe‐Ni‐Si alloys at high pressure is important for constraining the thermal and compositional structure of Earth's core, where silicon is widely considered a major light element. However, large uncertainties remain due to methodological differences in melt‐detection criteria and limited measurements in the hexagonal close‐packed phase field. In this study, we sampled the phase diagram of from 58 to 157 GPa and temperatures up to 3500 K using synchrotron Mössbauer spectroscopy (SMS) that monitors the atomic dynamics of iron nuclei, and synchrotron X‐ray diffraction (XRD) to detect liquid diffuse scattering. SMS measurements constrained the solidus by tracking the collapse of hyperfine parameters across the solid–liquid boundary. Complemented by burst‐heating XRD with pixel‐level background analysis that enables robust identification of the appearance of liquid diffuse scattering, this dual‐technique approach provides a precise determination of the solidus. Our results demonstrate that silicon significantly lowers the solidus temperatures of Fe‐Ni alloys in both and structures, and the ‐‐ liquid quasi‐triple point occurs at GPa and K. At the highest solidus pressure of 150 GPa, we determine a low solidus temperature of K. This integrated framework enables a more precise determination of the solidus and provides broader insight into melting detection strategies relevant to Earth's deep interior.