In this study, we demonstrate that it is possible to fit the resilience at the high temperature limit using only the atomic mean square displacement determined from cryogenic temperature single crystal diffraction data. Our method introduces the Debye phonon model, under which the atomic mean square displacement displays quantum behavior at cryogenic temperatures and deviates from a linear temperature dependence. From the resilience of Si extrapolated from cryogenic temperature X-ray diffraction data, one can calculate the Si isotope fractionation using our recently developed force constants approach. We applied our method to epidote and coesite, which are common minerals in ultra-high pressure metamorphic rocks, and our predicted Si isotope fractionation ln alpha Si30/28 are consistent with mass spectroscopy observations of Delta 30Si in Dabie eclogite and Alps whiteschist. Our results indicate that the geofluid involved in the fluid-rock interaction in Dabie and Alps orogens doesn't significantly alter the Si-isotope composition of ultrahigh pressure metamorphism. Our manuscript presents a novel experimental methodology to determine the high-temperature resilience and equilibrium isotope fractionation factors of silicon in minerals, which can be applied to the metastable upper mantle silicates that are non-quenchable at high temperatures and room pressure.

Davemaoite (CaSiO3 perovskite) is the third most abundant mineral in Earth's lower mantle and a dominant phase in subducted oceanic crust. Its crystal structure is distorted (tetragonal or orthorhombic) at ambient conditions but is considered to transform to cubic at high temperatures. Previous experiments reported low, nearly pressure-independent transition temperatures (approximately 600 K), demonstrating a long-standing discrepancy with theoretical predictions that mostly exceed 1000 K. Here, we determine the phase stability and thermal equation of state of CaSiO3 davemaoite and its titanium-bearing solid solution [Ca(Si0.75,Ti0.25)O3] under simultaneous high-pressure and high-temperature conditions using a laser-heated diamond anvil cell combined with synchrotron X-ray diffraction. We find that the tetragonal-to-cubic transition occurs at substantially higher temperatures than previously reported, with the titanium substitution further stabilizing the tetragonal phase and shifting the transition boundary to even higher temperatures. These findings indicate that CaSiO3 davemaoite in subducted oceanic crust likely undergoes its ferroelastic transition in the mid-lower mantle, whereas Ti-rich davemaoite may remain tetragonal throughout most of the lower mantle, transforming to cubic near the core-mantle boundary. Our results demonstrate that the compositionally dependent phase behaviour of davemaoite can account for the seismic anomalies observed in both the mid-lower mantle and the lowermost mantle.

Mercury’s highly reduced formation conditions likely promoted the incorporation of silicon into its metallic core during planetary differentiation. The resulting Si-rich core composition would reduce the capacity of the metallic liquids to dissolve carbon, making carbon saturation more likely as the core cooled and crystallized. Determining the solubility of carbon in Fe-Si liquids under Mercury’s core conditions is therefore essential for evaluating whether graphite or diamond could precipitate from the core and influence Mercury’s thermal and magnetic evolution. In this study, high-pressure and high-temperature experiments were conducted on carbon-saturated Fe-Si alloys with varying silicon content from 4 to 27 wt% using a multi-anvil press at 5–20 GPa and 1673–1873 K. The analyses of the recovered samples by Scanning Electron Microscope (SEM) and Raman spectroscopy show the Fe-Si-C liquids with precipitated carbon phases in the form of graphite or diamond. Quantitative electron probe microanalysis (EPMA) results demonstrate a trend of decreasing carbon content in the Fe-Si-C alloys with increasing silicon content, described by the following equation: CFe-Si = 8.45–0.663[Si] + 0.0134[Si]2. Higher initial silicon content within Mercury’s core due to the highly reduced conditions may result in lower solubility of carbon, suggesting a potential mechanism for the preferential exsolution of carbon-rich materials, such as graphite or diamonds. This finding suggests that carbon could precipitate within Mercury’s cooling, solidifying core under Mercurian core compositions and conditions. The segregation and accumulation of carbon could modify heat flux across the core-mantle boundary, affecting both the strength of Mercury’s early magnetic field and the longevity of dynamo action. Such compositional convection could sustain a dynamo, contributing to Mercury’s present-day magnetic field.

Abstract Impedance spectrometry experiments have been conducted on CaCO3 up to 15 GPa and 2,100 K to identify its state under high pressure. The melting temperature of CaCO3 was also determined by the falling of a Re sphere observed via X‐ray radiography. The phase transition from aragonite to the amorphous phase does not cause a leap in the Electrical conductivity (EC), while a drastic increase in the EC, by 1.5–2.0 log units, only occurs with the onset of melting. The EC of amorphous CaCO3 is comparable to other hydrous mantle minerals at similar pressure and temperature conditions. The required fraction of amorphous CaCO3 implies that it can be excluded from the potential origins responsible for the observed high EC anomalies in the upper mantle. If the conductivity anomalies are induced by the presence of carbonate, a low‐degree melting of carbonate‐bearing peridotite is anticipated.

Most nitrogen is predicted to reside in the Earth’s interior and could be in the form of nitrides. In this study, the chemical reaction of Si3N4 with SiO2 was explored up to 50 GPa and 2 600 K using laser-heated diamond anvil cells combined with synchrotron radiation X-ray diffraction. The experimental results demonstrate that Si3N4 does not react with SiO2 and cubic γ-Si3N4 remains stable at extreme pressure and temperature. First-principles calculations were performed to investigate the chemical stability of Si3N4 with the SiO2-MgO assemblage, showing that Si3N4 can coexist with Mg2SiO4 and MgSiO3 polymorphs. Based on our thermal equation of state of cubic γ-Si3N4, we suggest that cubic γ-Si3N4 is denser than the upper mantle but less dense than the lower mantle. The formation of Si3N4 in the early Earth may contribute to the nitrogen preservation in the deep mantle soon after crystallization of the mantle and Si3N4 is likely a precursor of nitrogen hosts in the modern deep Earth.

Electrical conductivity (EC) provides important constraints on the composition and volatile distribution of Earth's deep mantle, yet the EC of davemaoite (CaSiO3 perovskite), a major lower-mantle phase, remains poorly constrained. We measured the EC of nominally dry CaSiO3 perovskite at pressures up to 89 GPa and temperatures up to 2200 K using impedance spectroscopy in a laser-heated diamond anvil cell. Conductivity increases with temperature but decreases systematically with pressure and it is substantially lower than previously reported, yet broadly consistent with recent theoretical predictions for oxygen-vacancy-mediated ionic transport. A distinct change in the temperature dependence coincides with the tetragonal-to-cubic phase boundary, revealing a modest enhancement of ionic transport across the structural transition. Along a normal lower-mantle geotherm, dry davemaoite is comparable in conductivity to bridgmanite near the top of the lower mantle but becomes progressively less conductive with depth. Under cold-slab conditions, dry davemaoite is substantially less conductive than dry subducted MORB and cannot account for the observed high-conductivity anomalies. Dry davemaoite therefore contributes little to bulk lower-mantle conductivity.

Using our recently developed X‐ray diffraction based force constants approach, we have determined the equilibrium Si isotope fractionation between omphacite/garnet, quartz/kyanite, and quartz/zircon at temperatures relevant to the petrogenesis. We find that Na strongly affects the Si isotope fractionation between omphacite and garnet. Our results have suggested that the omphacite and garnet in eclogite collected in the Dabie Mountain, as well as the kyanite and its host quartz veins, are isotopically in equilibrium, which further suggests that the Dabie Mountain eclogites and its host veins underwent the same high pressure‐temperature condition during their formation. The Si isotope fractionation determined by our methods, together with published mass spectroscopy measurements, DFT‐CIPW calculations and sigmoid fitting on various felsic granites, have suggested that the Si isotope fraction between zircon and whole rock “saturates” at ∼0.45‰ at 1000 K when the SiO 2 content in the granite is above ∼70 wt%.

The incorporation of ferric iron in mantle silicates stabilizes different crystal structures and changes phase transition conditions, thus impacting seismic wave speeds and discontinuities. Recent experiments of MgSiO3-Fe2O3 mixtures indicate the coexistence of fully oxidized iron-rich (Mg0.5Fe0.53+)(Fe-0.53+Si-0.5)O-3 with Fe-poor silicate (wadsleyite or bridgmanite) and stishovite at 15 to 27 GPa and 1773 to 2000 K, conditions relevant to subducted lithosphere in the Earth's transition zone and uppermost lower mantle. X-ray diffraction (XRD) shows that (Mg0.5Fe0.53+)(Fe0.53+Si0.5)O-3 recovered from these conditions adopts the R3c LiNbO3-type structure, which transforms to the bridgmanite structure again between 18.3 and 24.7 GPa at 300 K. XRD data are used to obtain the equation of state of the LiNbO3-type phase up to 18.3 GPa. Combined with multi-anvil experiments, these observations suggest that the stable phase of (Mg0.5Fe0.53+)(Fe0.53+Si0.5)O-3 is bridgmanite at 15-27 GPa, which transforms on decompression to LiNbO3-type structure. Our calculation revealed that ordering of the ferric ion reduces the kinetic energy barrier of the transition between (Mg0.5Fe0.53+)(Fe0.53+Si0.5)O-3 LiNbO3 structure and bridgmanite relative to the MgSiO3 akimotoite-bridgmanite system. A dense Fe3+-rich bridgmanite structure is thus stable at substantially shallower depths than MgSiO3 bridgmanite and would promote subduction.

Carbon and hydrogen are both potential light elements in the Earth's core. However, the stability and elastic properties of Fe-C-H ternary alloy under high pressure have rarely been explored. In this study, we synthesized a new hcp-structured Fe-C-H alloy (FeC0.065H1.05) at high pressure using the laser-heated diamond anvil cell. Hydrogen incorporation significantly expands the volume and decreases the bulk modulus of hcp Fe and Fe-C alloy (FeC0.065). It also elevates the c/a ratio, potentially explaining the anisotropy of the Earth's inner core. Furthermore, the incorporation of carbon and hydrogen considerably decreases the density of hcp Fe. 0.3-0.7 wt.% H and 0.2-0.5 wt.% C in Fe alloys could account for the observed density deficit of the inner core with 7,000-5,000 K inner core boundary temperature. A tradeoff relationship was established that the effect of 4 wt.% carbon is equivalent to 1 wt.% hydrogen on the density of inner core.

Raman spectroscopy is a rapid, nondestructive analysis technique used in various scientific disciplines, including mineralogy, chemistry, materials science, and biology. The analysis of Raman spectra and the identification of specific substances in unknown samples can be complex and time-consuming due to the large database of Raman spectra. The Raman Match application was developed to simplify and automate the sample identification process through a search and match method. The application integrates the well-established RRUFF Raman database with the Python programming language. It provides a user-friendly graphical interface to load Raman spectra, identify and fit peaks, match peaks to the reference libraries, visualize the results, and generate publication-ready figures. The application offers a swift and automated method for mineral identification using Raman spectroscopy in laboratory and field settings and during planetary exploration missions to extraterrestrial environments with constraints on time and resources.

Superdeep diamonds and their syngenetic inclusions are crucial for understanding Earth’s deep carbon cycle and slab–mantle redox dynamics. The origins of these diamonds, especially their links to iron (Fe) carbides and ferropericlase with varying Mg# [=Mg/(Mg+Fe)at], however, remain elusive. In this study, we performed high pressure–temperature (P-T) experiments (10–16 GPa and 1200–1700 K) across cold-to-warm subduction zones using a multi-anvil press. The results reveal a stepwise Fe-mediated carbonate reduction process for the formation of superdeep diamonds: MgCO3 → Fe-carbides (Fe3C/Fe7C3) → graphite/diamond. This mechanism explains two phenomena regarding superdeep diamonds: (1) anomalous 13C depletion results from kinetic isotope fractionation during 12C enrichment into the intermediate Fe-carbides; (2) nitrogen scarcity is due to Fe-carbides acting as nitrogen sinks. Ferropericlase [(Mg,Fe)O] formed during the reactions in our experiments shows Mg# variations (0.2–0.9), similar to those found in natural samples. High Mg# (>0.7) variants from lower temperature experiments indicate diamond crystallization from carbonatitic melts in the shallow lower mantle, while the broad Mg# range (0.2–0.9) from experiments at higher temperatures suggests multi-depth formation processes as found in Brazilian diamonds. These findings suggest that slab–mantle interactions produce superdeep diamonds with distinctive Fe-carbides and ferropericlase assemblages as inclusions, coupled with their 13C- and nitrogen-depleted signatures, which underscore thermochemical carbon cycling as a key factor in deep carbon storage and mantle mineralogy.

Hydrogen-terminated nanodiamonds are new functional nanodiamonds that have many applications, particularly in the field of catalysis. However, their elastic properties have not yet been investigated. In this study, hydrogen-terminated nanodiamonds were synthesized at 15.5 GPa and 1200-1600 °C using trans-stilbene (C14H12) as the starting material in a relatively closed carbon-hydrogen system by using a gold capsule. Raman spectroscopy revealed characteristic diamond peaks, with a set of peaks around 2900 cm-1 indicating hydrogen termination. The extent of hydrogenation and unit-cell volume are negatively correlated to the synthetic temperature, while the grain size is positively correlated to it. The size of the synthesized hydrogen-terminated nanodiamonds at 15.5 GPa and 1600 °C was confirmed to be ∼6-15 nm by synchrotron-based X-ray diffraction and transmission electron microscopy. Their equation of state was determined by synchrotron-based X-ray diffraction combined with the diamond anvil cell up to 33.6 GPa. The bulk modulus was determined to be 424(12) GPa, lower than the bulk moduli of the bulk diamond and conventional nanodiamonds. It indicates that hydrogen termination softens nanodiamonds and may play a vital role in modifying their elastic behavior.

Subduction of oceanic lithosphere effectively transports substantial amounts of water deep into the Earth, altering the properties of the surrounding mantle minerals and facilitating chemical interactions between the subducting lithosphere and mantle. Ice-VII is considered the stable phase of H2O released from minerals within the cold subducting slabs by progressive dehydration. This study investigates the melting boundary of high-pressure ices and the transformation of ice-VII to superionic (SI) states under the specific pressure-temperature (P-T) conditions of subducting slabs. We conducted X-ray diffraction measurements on H2O phases up to 42 GPa and 1400 K using a newly developed externally-heated diamond anvil cell system with precise P-T control. The experiments confirm the elevated melting temperature of high-pressure ice starting at 9.5 GPa, likely due to the appearance of SI body-centered cubic ice phase. The phase diagram of H2O, particularly the elevated melting temperatures and transition to SI state, provides crucial insights into the role of water in cold subducting slabs and its possible association with deep-seated seismic activity and mantle dynamics.

The Brillouin scattering technique is crucial in geosciences and material sciences because it allows for the accurate determination of elastic properties of materials, which are essential for understanding their behavior and stability under various conditions. BrillouinView is an open-source software program developed in Python, designed to seamlessly integrate the calibration, visualization, and fitting of Brillouin scattering data with single-crystal elasticity modeling. Despite its importance in geosciences and materials sciences, the Brillouin scattering technique has historically lacked feature-rich, functional analysis and modeling software due to its complexity and the need for precise calibration and fitting techniques. BrillouinView addresses these challenges by providing a comprehensive toolkit that simplifies and enhances the analysis process.

Hydrous phases are often considered important hydrogen carriers in the subducted slabs, but their stabilities under the reduced oxidation state have rarely been investigated. Previous studies suggested that metallic iron can be present in the mantle and subducted slabs at depth through disproportionation and serpentinization of silicates. Here we show that hydrous phases in the subducted slabs such as superhydrous phase B, phase E, and phase Egg react with metallic iron to produce less hydrous or anhydrous silicates, oxides, and H2 in the deep mantle. The produced H2 can ascend and react with Fe3+-bearing silicates in the overlying mantle, leading to the formation of hydrous phases and melts. The high mobility of H2 fluid compared with hydrous species will expedite the deep hydrogen cycle. Meanwhile, the oxidation states of subducted slab and various mantle layers will undergo gradual homogenization as a result of coupled redox dehydrogenation and hydration processes.

Carbon and nitrogen are considered as candidate light elements present in planetary cores. However, there is limited understanding regarding the structure and physical properties of Fe-C-N alloys under extreme conditions. Here diamond anvil cell experiments were conducted, revealing the stability of hexagonal-structured Fe7(N0.75C0.25)3 up to 120 GPa and 2100 K, without undergoing any structural transformation or dissociation. Notably, the thermal expansion coefficient and Gr & uuml;neisen parameter of the alloy exhibit a collapse at 55-70 GPa. First-principles calculations suggest that such anomaly is associated with the spin transition of iron within Fe7(N0.75C0.25)3. Our modeling indicates that the presence of similar to 1.0 wt% carbon and nitrogen in liquid iron contributes to 9-12% of the density deficit of the Earth's outer core. The thermoelastic anomaly of the Fe-C-N alloy across the spin transition is likely to affect the density and seismic velocity profiles of (C,N)-rich planetary cores, thereby influencing the dynamics of such cores. A significant amount of light elements are believed to be present in the cores of Earth and other planets to explain the density difference between iron-nickel alloys and geophysical observations. This study used experiments at high-pressure and high-temperature conditions and theoretical simulations to investigate a specific candidate phase of the core called Fe7(N0.75C0.25)3, which has a hexagonal structure, at high pressures similar to those in planetary cores. This phase did not undergo any major structural changes under the conditions investigated. However, its properties related to the thermoelastic behaviors showed significant changes between 55 and 70 GPa. Theoretical calculations indicate that this anomalous behavior is linked to the magnetic transition within h-type Fe7(N0.75C0.25)3. These findings suggest that the characteristics of a planetary core would be altered in the transition region, leading to a more complex thermal evolution than previously believed. This study provides insights into the behavior of light elements in planetary cores and its implications for planetary dynamics. The h-type Fe7(N0.75C0.25)3 is stable to 120 GPa and 2100 K, but undergoes a pressure-induced spin transition Spin transition causes a significant reduction in gamma 0 and alpha 0, and the thermal equation of state of h-type non-magnetic Fe7(C,N)3 is determined The density profile and seismic features of a planetary core could be altered across the spin transition, which may affect core dynamics

Carbonates or carbon-bearing materials may release gases under high pressure and high temperature (HP-HT) conditions. Characterizing the species and quantifying the volumes of these carbonaceous gases are critical for understanding carbon chemistry. However, the volatile nature of carbonaceous gas poses technical challenges in their collection, speciation, and quantification during HP-HT experiments. To address these challenges, we have developed a system that integrates sample collection, gas transportation, chemical conversion, and measurement of carbonaceous gases trapped within the large volume press capsules. The system comprises a capsule-crushing device for thorough sample pulverization, a mechanizer coupled with a flame ionization detector, a gas-sealing and transport interface, and gas chromatography for detection. To evaluate the system's capabilities, we quantified the gas volumes released from encapsulated kerogen quenched from 1.9 GPa to 873, 973, and 1073 K. The collected gas chromatography signals were compared to those obtained from standard mixed-gases. The volumes of CO2, CH4, and C2H6 in the samples were successfully derived from the signal peak area through calibration. The relative standard deviation value of two runs at 3 GPa and 1073 K is 1.956%, suggesting good reproducibility. Our system thus provides a robust solution for investigating carbon chemistry under HP-HT conditions.

Davemaoite (CaSiO3 perovskite) is considered the third most abundant phase in the pyrolytic lower mantle and the second most abundant phase in the subducted mid-ocean ridge basalt (MORB). During the partial melting of the pyrolytic upper mantle, incompatible titanium (Ti) becomes enriched in the basaltic magma, forming Ti-rich MORB. Davemaoite is considered an important Ti-bearing mineral in subducted slabs by forming a Ca(Si,Ti)O-3 solid solution. However, the crystal structure and compressibility of Ca(Si,Ti)O-3 perovskite solid solution at relevant pressure and temperature conditions had not been systematically investigated. In this study, we investigated the structure and equations of state of Ca(Si0.83Ti0.17)O-3 and Ca(Si0.75Ti0.25)O-3 perovskites at room temperature up to 82 and 64 GPa, respectively, by synchrotron X-ray diffraction (XRD). We found that both Ca(Si0.83Ti0.17)O-3 and Ca(Si0.75Ti0.25)O-3 perovskites have a tetragonal structure up to the maximum pressures investigated. Based on the observed data and compared to pure CaSiO3 davemaoite, both Ca(Si0.83Ti0.17)O-3 and Ca(Si0.75Ti0.25)O-3 perovskites are expected to be less dense up to the core-mantle boundary (CMB), and specifically similar to 1-2% less dense than CaSiO3 davemaoite in the pressure range of the transition zone (15-25 GPa). Our results suggest that the presence of Ti-bearing davemaoite phases may result in a reduction in the average density of the subducting slabs, which in turn promotes their stagnation in the lower mantle. The presence of low-density Ti-bearing davemaoite phases and subduction of MORB in the lower mantle may also explain the seismic heterogeneity in the lower mantle, such as large low shear velocity provinces (LLSVPs).

Accurate knowledge of the phase transitions and thermoelastic properties of candidate iron alloys, such as Fe-Si alloys, is essential for understanding the nature and dynamics of planetary cores. The phase diagrams of some Fe-Si alloys between 1 atm and 16 GPa have been back-extrapolated from higher pressures, but the resulting phase diagram of Fe83.6Si16.4 (9 wt.% Si) is inconsistent with temperature-induced changes in its electrical resistivity between 6 and 8 GPa. This study reports in situ synchrotron X-ray diffraction (XRD) measurements on pre-melted and powder Fe83.6Si16.4 samples from ambient conditions to 60 GPa and 900 K using an externally heated diamond-anvil cell. Upon compression at 300 K, the bcc phase persisted up to similar to 38 GPa. The hcp phase appeared near 8 GPa in the pre-melted sample, and near 17 GPa in the powder sample. The appearance of the hcp phase in the pre-melted sample reconciles the reported changes in electrical resistivity of a similar sample, thus resolving the low-pressure region of the phase diagram. The resulting high-temperature Birch-Murnaghan equation of state (EoS) and thermal EoS based on the Mie-Gruneisen-Debye model of the bcc and hcp structures are consistent with, and complement the literature data at higher pressures. The calculated densities based on the thermal EoS of Fe-9wt.%Si indicate that both bcc and hcp phases agree with the reported core density estimates for the Moon and Mercury.