Laser-heated Diamond Anvil Cell Research Articles

Compression of liquid Ni and Co under extreme conditions explored by x-ray absorption spectroscopy

The compression of liquid nickel and cobalt has been investigated up to 102 and 83 GPa, respectively, by x-ray absorption spectroscopy at the Ni and Co $K$ edges, using laser-heated diamond anvil cell. A shortening of about 8%--10% of the metal bond distances is observed in the pressure range considered and the experimental results are confirmed by theoretical calculations. Ab initio quantum molecular dynamics calculations have been performed, providing a model pair distribution function for cobalt, used as a starting model in the extended x-ray absorption fine structure analysis. The specific volume of the liquid has also been estimated and compared to calculations in the literature. This work sets the basis for x-ray absorption spectroscopy studies of liquid metals under extreme conditions with potentially important implications for the understanding of Earth and planetary interiors.

Nitride Spinel: An Ultraincompressible High-Pressure Form of BeP2 N4.

Owing to its outstanding elastic properties, the nitride spinel γ‐Si3N4 is of considered interest for materials scientists and chemists. DFT calculations suggest that Si3N4‐analog beryllium phosphorus nitride BeP2N4 adopts the spinel structure at elevated pressures as well and shows outstanding elastic properties. Herein, we investigate phenakite‐type BeP2N4 by single‐crystal synchrotron X‐ray diffraction and report the phase transition into the spinel‐type phase at 47 GPa and 1800 K in a laser‐heated diamond anvil cell. The structure of spinel‐type BeP2N4 was refined from pressure‐dependent in situ synchrotron powder X‐ray diffraction measurements down to ambient pressure, which proves spinel‐type BeP2N4 a quenchable and metastable phase at ambient conditions. Its isothermal bulk modulus was determined to 325(8) GPa from equation of state, which indicates that spinel‐type BeP2N4 is an ultraincompressible material.

High-temperature electrical resistivity measurements of hcp iron to Mbar pressure in an internally resistive heated diamond anvil cell

ABSTRACTElectrical and thermal transport properties of iron are of great importance for understanding the thermal evolution and dynamics of the Earth’s core, of which iron is a major component. However, the reported values of iron’s conductivity at core conditions are still highly controversial. In this study, we employed an internally resistive heated diamond anvil cell (IHDAC) technique that reduces temperature heterogeneity inside the heated sample, and revisited the electrical resistivity of hexagonal closed packed (hcp) iron up to 110 GPa and 2500 K. Our results are in complete agreement with the reported values of the high pressure-temperature electrical resistivity of hcp iron obtained by using the laser-heated diamond anvil cell technique, supporting high iron conductivity at the Earth’s core conditions. The high pressure-temperature resistivity measurement in an IHDAC employed here would be a more suitable method to examine more resistive iron alloys at the Earth’s core conditions.

Synthesis of clathrate cerium superhydride CeH9 at 80-100 GPa with atomic hydrogen sublattice

Hydrogen-rich superhydrides are believed to be very promising high-Tc superconductors. Recent experiments discovered superhydrides at very high pressures, e.g. FeH5 at 130 GPa and LaH10 at 170 GPa. With the motivation of discovering new hydrogen-rich high-Tc superconductors at lowest possible pressure, here we report the prediction and experimental synthesis of cerium superhydride CeH9 at 80–100 GPa in the laser-heated diamond anvil cell coupled with synchrotron X-ray diffraction. Ab initio calculations were carried out to evaluate the detailed chemistry of the Ce-H system and to understand the structure, stability and superconductivity of CeH9. CeH9 crystallizes in a P63/mmc clathrate structure with a very dense 3-dimensional atomic hydrogen sublattice at 100 GPa. These findings shed a significant light on the search for superhydrides in close similarity with atomic hydrogen within a feasible pressure range. Discovery of superhydride CeH9 provides a practical platform to further investigate and understand conventional superconductivity in hydrogen rich superhydrides.

Synthesis of Manganese Mononitride with Tetragonal Structure under Pressure

The exploration of the vast phase space of transition metal nitrides is critical for discovering novel materials and potential technological applications. Manganese mononitride with a tetragonal structure (space group I4/mmm) was synthesized in a laser-heating diamond anvil cell, which could be quenched to ambient pressure. The bulk modulus of 173 GPa was measured using in situ high-pressure diffraction, and the axial compressibility shows that, under pressure, the a direction is much more compressible than the c direction in tetragonal MnN. DFT results with correction of the on-site repulsion (GGA + U) confirm that tetragonal MnN is energetically stable and antiferromagnetic. This study highlights the need to include on-site repulsion to understand 3d metal nitrides.

In situ characterization of the high pressure \u2013 high temperature melting curve of platinum

In this work, the melting line of platinum has been characterized both experimentally, using synchrotron X-ray diffraction in laser-heated diamond-anvil cells, and theoretically, using ab initio simulations. In the investigated pressure and temperature range (pressure between 10 GPa and 110 GPa and temperature between 300 K and 4800 K), only the face-centered cubic phase of platinum has been observed. The melting points obtained with the two techniques are in good agreement. Furthermore, the obtained results agree and considerably extend the melting line previously obtained in large-volume devices and in one laser-heated diamond-anvil cells experiment, in which the speckle method was used as melting detection technique. The divergence between previous laser-heating experiments is resolved in favor of those experiments reporting the higher melting slope.

Profound softening and shear-induced melting of diamond under extreme conditions: An ab-initio molecular dynamics study

Diamond retains original crystal form and large elastic stiffness up to very high temperatures, and strengthens considerably under high pressures. These remarkable characters dictate its behaviors under extreme loadings such as those in laser-heated diamond anvil cells (LHDACs) or giant planetary interiors. Here we report surprising findings from ab initio molecular dynamics simulations revealing that diamond's mechanical strengths reduce precipitously at elevated temperatures, by 50% at 3000 K, despite that its elastic parameters remain little changed. Our results also unravel an extraordinary shear-induced reduction of melting temperature of diamond under (111)[112¯] shear strains by as much as 1150 K, greatly altering its pressure-temperature (p−T) phase diagram when shear deformations exist. These new benchmarks offer crucial insights for elucidating extreme mechanics of diamond at high p-T conditions, advancing fundamental knowledge with major implications for LHDAC operation and planetary modeling.

The stability of Fe5O6 and Fe4O5 at high pressure and temperature

Abstract The oxygen fugacity in the interior of the Earth is largely controlled by iron-bearing minerals. Recent studies have reported various iron oxides with chemical compositions between FeO and Fe3O4 above ~10 GPa. However, the stabilities of these high-pressure iron oxides remain mostly uninvestigated. In this study, we performed in situ X-ray diffraction (XRD) measurements in a laser-heated diamond-anvil cell (DAC) to determine the phase relations in both Fe5O6 and Fe4O5 bulk compositions to 61 GPa and to 2720 K. The results show that Fe5O6 is a high-temperature phase stable above 1600 K and ~10 GPa, while FeO + Fe4O5 are formed at relatively low temperatures. We observed the decomposition of Fe5O6 into 2FeO + Fe3O4 above 38 GPa and the decomposition of Fe4O5 into FeO + h-Fe3O4 at a similar pressure range. The coexistence of FeO and Fe3O4 indicates that none of the recently discovered compounds between FeO and Fe3O4 (i.e., Fe5O6, Fe9O11, Fe4O5, and Fe7O9) are formed beyond ~40 GPa at 1800 K, corresponding to conditions in the shallow lower mantle. Additionally, as some superdeep diamonds have genetic links with these high-pressure iron oxides, our results give constraints on pressure and temperature conditions of their formation.

Phase relations of MgSiO3-FeSiO3 system up to 64 GPa and 2300 K using multianvil apparatus with sintered diamond anvils

We have developed techniques to perform precise determinations of phase transition boundaries under the pressure and temperatures corresponding to those of the deep lower mantle, using Kawai-type multianvil apparatus (KMA) with sintered diamond anvils. By optimizing the materials and dimensions of the high-pressure furnace assembly, we achieved stable generation of high temperature to 2300 K, at pressures up to ~64 GPa, which is the highest temperature reported in KMA under such high pressure conditions. Phase relations in the MgSiO3-FeSiO3 system have been studied at pressures from 27 to 64 GPa and temperatures of 1800–2300 K by in situ X-ray diffraction measurements, combined with quench experiments, using synthetic pyroxene samples with chemical compositions of FeSiO3 and (Mg0.4Fe0.6)SiO3 as the starting materials. Our results show that the iron content in MgSiO3 bridgmanite increases almost linearly up to 42 mol% of the FeSiO3 component with increasing pressure in this pressure and temperature range. For higher iron proportions, an assemblage of bridgmanite + magnesiowüstite + stishovite is formed, while the oxide mixture of magnesiowüstite and stishovite is stable for the compositions close to FeSiO3. Our results suggest that bridgimanite with the pure FeSiO3 composition should only be formed at pressures significantly higher than 64 GPa, contradictory to some recent studies using laser-heated diamond anvil cell. It is also suggested that magnesiowüstite inclusions with various iron contents found in some natural diamonds may reflect the formation of magnesiowüstite in former oceanic crust material subducted into the uppermost lower mantle.

High-pressure melting curve of sulfur up to 65 GPa

The melting curve of elemental sulfur was measured to pressures of 65 GPa in a laser-heated diamond-anvil cell using ex situ textural analyses combined with spectroradiometry and benchmarked with laser-power-temperature functions. The melting curve reaches temperatures of $\ensuremath{\sim}1800\phantom{\rule{0.28em}{0ex}}\mathrm{K}$ by 65 GPa and is smooth in the range of 23--65 GPa with a Clapeyron slope of $\ensuremath{\sim}14\phantom{\rule{0.28em}{0ex}}\mathrm{K}/\mathrm{GPa}$ at 23 GPa. This is consistent with melting of a single tetragonal sulfur structure in this range, which is confirmed by in situ x-ray diffraction. An updated equation of state for tetragonal sulfur is determined, and the high-pressure, high-temperature stability region of tetragonal sulfur is reassessed.

Melting curve of elemental zirconium

Melting experiments require rapid data acquisition due to instabilities of the molten sample and optical drifting due to the high required laser power. In this work, the melting curve of zirconium has been determined up to 80 GPa and 4000 K using in situ fast x-ray diffraction (XRD) in a laser-heated diamond anvil cell. The main method used for melt detection was the direct observance of liquid diffuse scattering in the XRD patterns and it has been proven to be a reliable melting diagnostic. The effectiveness of other melting criteria such as the appearance of temperature plateaus with increasing laser power is also discussed.

Stability of Fe-bearing hydrous phases and element partitioning in the system MgO–Al2O3–Fe2O3–SiO2–H2O in Earth's lowermost mantle

We performed high pressure–temperature (P-T) experiments on a model composition of hydrous subducted slabs in the MgO–Al2O3–Fe2O3–SiO2–H2O system using laser-heated diamond anvil cells. The phase assemblages were characterized combining in-situ synchrotron X-ray diffraction and ex-situ transmission electron microscope techniques. The hydrous δ-phase AlOOH–FeOOH–MgSiO2(OH)2–SiO2 coexists with bridgmanite (Bdg), post-perovskite (pPv), or both in a broad P-T range of 104–126 GPa and 1750–2500 K. The hydrous pyrite-type FeOOHx phase was observed in-situ over a P-T range of 112–123 GPa and 1750–2300 K, coexisting with the pPv phase. Chemical analysis on recovered samples showed that considerable amount of Fe2O2(OH)2 (8–13 mol%) and SiO2 (9–13 mol%) in the δ-phase does not reduce its thermal stability compared to the Al-endmember, indicating that the Fe-bearing δ-phase can transport water to the lowermost mantle along the mantle geotherm. In this hydrous system, we observed that Al depletion in both the Bdg and pPv phases can significantly reduce the width of the Bdg to pPv transition in contrast to a wide two-phase coexistence region in a dry Al-rich system. Meanwhile, the Fe enrichment in the pPv phase relative to the coexisting Bdg phase lowers the transition pressure to the depth of the D″ discontinuity. Accordingly, the depth and thickness of the Bdg to pPv transition in subducted basaltic crustal materials can explain the seismically detected D″ discontinuity. Partial melting could be triggered by dehydration of the Fe-bearing hydrous phases due to a steep temperature gradient at the core mantle boundary (CMB), and therefore the ultralow-velocity zones (ULVZs) might be the regions where partial melting occurs at the lowermost mantle.

Combination of pulsed light heating thermoreflectance and laser-heated diamond anvil cell for in-situ high pressure-temperature thermal diffusivity measurements.

By combining thermoreflectance measurements and laser heated diamond anvil cell (LHDAC) techniques, an instrument for the measurement of in situ high pressure-temperature thermal diffusivity of materials was developed. In an LHDAC system, high-power continuous-wave laser beams irradiate both faces of a disk-shaped metal sample loaded into diamond anvil cells (DACs), to maintain a stable high-temperature condition. During the operation of the LHDAC system, temperature of the sample is determined from the thermal radiation spectrum between 640 and 740 nm to fit Planck's law. Subsequently, a pulsed laser beam irradiates the metal disk to induce a temperature gradient inside the sample, and the transient temperature, caused by heat diffusion, is measured by a continuous wave probe laser based on the thermoreflectance phenomenon. We determined the thermal conductivities of Pt and Fe up to approximately 60 GPa and 2000 K using the measured thermal diffusivities and obtained values consistent with previous works. The uncertainties in the pressure and the temperature are estimated to be approximately 10%, and that in the thermal conductivity is estimated to approximately 15%. The system developed in this study enables us to determine thermal transport properties of materials under pressure-temperature conditions of the deep Earth.

High-pressure synthesis of the BiVO3 perovskite

We report the high-pressure, high-temperature synthesis of $\mathrm{BiV}{\mathrm{O}}_{3}$, a cubic perovskite that thus far has remained inaccessible under ambient pressure conditions. We created this material at $\ensuremath{\sim}25$ GPa and 1500 K in a laser-heated diamond-anvil cell and recovered it to ambient pressure and temperature. Our synthetic approach circumvents the oxidative chemistry that, at ambient pressures, previously rendered the cubic $\mathrm{BiV}{\mathrm{O}}_{3}$ perovskite inaccessible. We find through density-functional theory calculations that this material is a unique metallic and antiferromagnetic transition-metal oxide.

Magnetism in cold subducting slabs at mantle transition zone depths.

The Earth's crust-mantle boundary, the Mohorovičić discontinuity, has been traditionally considered to be the interface between the magnetic crust and the non-magnetic mantle1. However, this assumption has been questioned by geophysical observations2,3 and by the identification of magnetic remanence in mantle xenoliths4, which suggest mantle magnetic sources. Owing to their high critical temperatures, iron oxides are the only potential sources of magnetic anomalies at mantle depths5. Haematite (α-Fe2O3) is the dominant iron oxide in subducted lithologies at depths of 300 to 600 kilometres, delineated by the thermal decomposition of magnetite and the crystallization of a high-pressure magnetite phase deeper than about 600 kilometres6. The lack of data on the magnetic properties of haematite at relevant pressure-temperature conditions, however, hinders the identification of magnetic boundaries within the mantle and their contribution to observed magnetic anomalies. Here we apply synchrotron Mössbauer source spectroscopy in laser-heated diamond anvil cells to investigate the magnetic transitions and critical temperatures in Fe2O3 polymorphs7 at pressures and temperatures of up to 90 gigapascals and 1,300 kelvin, respectively. Our results show that haematite remains magnetic at the depth of the transition zone in the Earth's mantle in cold or very cold subduction geotherms, forming a frame of deep magnetized rocks in the West Pacific region. The deep magnetic sources spatially correlate with preferred paths of the Earth's virtual geomagnetic poles during reversals8 that might not reflect the geometry of the transitional field. Rather, the paths might be an artefact caused by magnetized haematite-bearing rocks in cold subducting slabs at mid-transition zone depths. Such deep sources should be taken into account when carrying out inversions of the Earth's geomagnetic data9, and especially in studies of planetary bodies thatno longer have a dynamo10, such as Mars.

Evidence for Fe-Si-O liquid immiscibility at deep Earth pressures

Seismic observations suggest that the uppermost region of Earth's liquid outer core is buoyant, with slower velocities than the bulk outer core. One possible mechanism for the formation of a stably stratified layer is immiscibility in molten iron alloy systems, which has yet to be demonstrated at core pressures. We find immiscibility between liquid Fe-Si and Fe-Si-O persisting to at least 140 GPa through a combination of laser-heated diamond-anvil cell experiments and first-principles molecular dynamics simulations. High-pressure immiscibility in the Fe-Si-O system may explain a stratified layer atop the outer core, complicate differentiation and evolution of the deep Earth, and affect the structure and intensity of Earth's magnetic field. Our results support silicon and oxygen as coexisting light elements in the core and suggest that [Formula: see text] does not crystallize out of molten Fe-Si-O at the core-mantle boundary.

Static compression of B2 KCl to 230 GPa and its P-V-T equation of state

The pressure-volume-temperature (P-V-T) measurements of the B2 (CsCl-type) phase of KCl were performed at 9–61 GPa/1500–2600 K and up to 229 GPa at room temperature, based on synchrotron X‑ray diffraction measurements in a laser-heated diamond-anvil cell (DAC). The nonhydrostatic stress conditions inside the sample chamber were critically evaluated based on the platinum pressure marker. With thermal annealing by laser after each pressure increment, the deviatoric stress was reduced to less than 1% of the sample pressure even at the multi-megabar pressure range. The obtained P-V-T data were fitted to the Vinet equation of state with the Mie-Grüneisen-Debye model for thermal pressure. The thermal pressure of KCl was found to be as small as ~10 GPa even at 3000 K at any given volume, which is only half of that of common pressure markers (i.e. Pt, Au, or MgO). Such a low-thermal pressure validates the use of a KCl pressure medium as a pressure marker at high temperatures.

Optical properties of high-pressure fluid hydrogen across molecular dissociation

Optical properties of compressed fluid hydrogen in the region where dissociation and metallization is observed are computed by ab initio methods and compared with recent experimental results. We confirm that at T > 3,000 K, both processes are continuous, while at T < 1,500 K, the first-order phase transition is accompanied by a discontinuity of the dc conductivity and the thermal conductivity, while both the reflectivity and absorption coefficient vary rapidly but continuously. Our results support the recent analysis of National Ignition Facility (NIF) experiments [Celliers PM, et al. (2018) Science 361:677-682], which assigned the inception of metallization to pressures where the reflectivity is ∼0.3. Our results also support the conclusion that the temperature plateau seen in laser-heated diamond-anvil cell (DAC) experiments at temperatures higher than 1,500 K corresponds to the onset of optical absorption, not to the phase transition.

Melting curve and chemical stability of ammonia at high pressure: Combined x-ray diffraction and Raman study

The melting curve and stability of ammonia (${\mathrm{NH}}_{3}$) is investigated up to 40 GPa and 3500 K by x-ray diffraction and Raman spectroscopy in the laser-heated diamond anvil cell. The ${\mathrm{NH}}_{3}$ samples were directly heated by the $10.6\phantom{\rule{0.16em}{0ex}}\ensuremath{\mu}\mathrm{m}$ radiation of a ${\mathrm{CO}}_{2}$ laser to reduce the risks of chemical reactions. Melting was unambiguously detected by the appearance of the liquid diffraction signal upon temperature increase. The melting temperature of ${\mathrm{NH}}_{3}$ is found to steadily increase with pressure up to 40 GPa, and the previously reported turnover is not observed. As a result, the melting line of ${\mathrm{NH}}_{3}$ is expected to cross the isentropes of Neptune and Uranus in the pressure range 55--65 GPa, implying the possible presence of superionic solid ${\mathrm{NH}}_{3}$ in these planets. Our x-ray and Raman measurements confirm the appearance of ${\mathrm{N}}_{2}$ and ${\mathrm{H}}_{2}$ upon heating the liquid phase from 6 to 40 GPa. But while the equilibrium $2{\mathrm{NH}}_{3}\ensuremath{\rightleftharpoons}{\mathrm{N}}_{2}+3{\mathrm{H}}_{2}$ balances towards the dissociated elements at low pressure and high temperature, ammonia is found to the more stable species in the range 20--40 GPa, 300--3000 K.

Unveiling a Novel, Cation-Rich Compound in a High-Pressure Pb-Te Binary System.

Because of the common oxidation states of group IV elements (+2 or +4) and group VI elements (−2), 1:1 and 1:2 are two typical stoichiometries found in the IV–VI compounds. Particularly, in the Pb–Te binary system, the 1:1 stoichiometric PbTe is believed to be the only stable compound. Herein, using evolutionary algorithms, density functional theory, a laser-heated diamond anvil cell, and synchrotron X-ray diffraction experiments, we discovered a novel Pb–Te compound with an unexpected stoichiometry of 3:2 above 20 GPa. This tetragonal Pb3Te2 is the one of the very few cation-rich compounds that has ever been discovered in the entire IV–VI binary system. Further analyses based on electron density distribution, electron localization function, and Bader charge have shown that this newly discovered compound has a mixed character of chemical bonding with a decreased ionicity. By further calculating the electron–phonon interaction, Pb3Te2 is predicted to exhibit a superconducting transition at low temperatures. The discovery of Pb3Te2 paves the way for further explorations of other novel cation-rich IV–VI group compounds.