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Germanates are often used as structural analogs of planetary silicates. We have explored the high-pressure phase relations in Mg2GeO4 using diamond-anvil cell experiments combined with synchrotron X-ray diffraction and computations based on density functional theory. Upon room temperature compression, forsterite-type Mg2GeO4 remains stable up to 30 GPa. At higher pressures, a phase transition to a forsterite-III type (Cmc21) structure was observed, which remained stable to the peak pressure of 105 GPa. Using a third-order Birch Murnaghan fit to the experimental data, we obtained V0 = 305.1(3) Å3, K0 = 124.6(14) GPa, and K 0 ′ = 3.86 (fixed) for forsterite-type Mg2GeO4 and V0 = 263.5(15) Å3, K0 = 175(7) GPa, and K 0 ′ = 4.2 (fixed) for the forsterite-III type phase. The forsterite-III type structure was found to be metastable when compared to the stable assemblage of perovskite/post-perovskite + MgO, as observed during laser-heating experiments. Understanding the phase relations and physical properties of metastable phases is crucial for studying the mineralogy of impact sites, understanding metastable wedges in subducting slabs, and interpreting the results of shock compression experiments. [ABSTRACT FROM AUTHOR]

The thermal equation of state (EoS) of a natural schorl has been determined at high temperatures up to 673 K and high pressures up to 15.5 GPa using in situ synchrotron X-ray diffraction combined with a diamond-anvil cell. The pressure-volume (P-V) data were fitted to a third-order Birch-Murnaghan EoS with V0 = 1581.45 ± 0.25 Å3, K0 = 111.6 ± 0.9 GPa, and K 0 ′ = 4.4 ± 0.2; additionally, when K 0 ′ was fixed at a value of 4, V0 = 1581.04 ± 0.20 Å3, and K0 = 113.6 ± 0.3 GPa. The V0 (1581.45 ± 0.25 Å3) obtained by the third-order Birch-Murnaghan EoS agrees well with the V0 (1581.45 ± 0.05 Å3) measured at ambient conditions. Furthermore, the axial compression data of schorl at room temperature were fitted to a "linearized" third-order Birch-Murnaghan EoS, and the obtained axial moduli for the a- and c-axes are Ka = 621 ± 9 GPa and Kc = 174 ± 2 GPa, respectively. Consequently, the axial compressibilities are βa = 1.61 × 10–3 GPa–1 and βc = 5.75 × 10–3 GPa–1 with an anisotropic ratio of βa:βc = 0.28:1.00, indicating axial compression anisotropy. In addition, the compositional effect on the axial compressibilities of tourmalines was discussed. Fitting our pressure-volume-temperature (P-V-T) data to a high-temperature third-order Birch-Murnaghan EoS yielded the following thermal EoS parameters: V0 = 1581.2 ± 0.2 Å3, K0 = 110.5 ± 0.6 GPa, K 0 ′ = 4.6 ± 0.2, (∂KT/∂T)P = –0.012 ± 0.003 GPa K–1 and αV0 = (2.4 ± 0.2) × 10–5 K–1. These parameters were compared with those of previous studies on other tourmalines, and the potential factors influencing the thermal EoS parameters of tourmalines were further discussed. [ABSTRACT FROM AUTHOR]

In this study, we conduct extensive high‐pressure experiments to investigate phase stability in the cobalt‐nitrogen system. Through a combination of synthesis in a laser‐heated diamond anvil cell, first‐principles calculations, Raman spectroscopy, and single‐crystal X‐ray diffraction, we establish the stability fields of known high‐pressure phases, hexagonal NiAs‐type CoN, and marcasite‐type CoN2 within the pressure range of 50–90 GPa. We synthesize and characterize previously unknown nitrides, Co3N2, Pnma‐CoN and two polynitrides, CoN3 and CoN5, within the pressure range of 90–120 GPa. Both polynitrides exhibit novel types of polymeric nitrogen chains and networks. CoN3 feature branched‐type nitrogen trimers (N3) and CoN5 show π‐bonded nitrogen chain. As the nitrogen content in the cobalt nitride increases, the CoN6 polyhedral frameworks transit from face‐sharing (in CoN) to edge‐sharing (in CoN2 and CoN3), and finally to isolated (in CoN5). Our study provides insights into the intricate interplay between structure evolution, bonding arrangements, and high‐pressure synthesis in polynitrides, expanding the knowledge for the development of advanced energy materials [ABSTRACT FROM AUTHOR]

Garnet is an important mineral phase in the upper mantle as it is both a key component in bulk mantle rocks, and a primary phase at high pressure within subducted basalt. Here, we focus on the strength of garnet and the texture that develops within garnet during accommodation of differential deformational strain. We use X-ray diffraction in a radial geometry to analyze texture development in situ in three garnet compositions under pressure at 300 K: a natural garnet (Prp60Alm37) to 30 GPa, and two synthetic majorite-bearing compositions (Prp59Maj41 and Prp42Maj58) to 44 GPa. All three garnets develop a modest (100) texture at elevated pressure under axial compression. Elasto-visco-plastic self-consistent (EVPSC) modeling suggests that two slip systems are active in the three garnet compositions at all pressures studied: {110} and {001}. We determine a flow strength of ~5 GPa at pressures between 10 to 15 GPa for all three garnets; these values are higher than previously reported yield strengths measured on natural and majoritic garnets. Strengths calculated using the experimental lattice strain differ from the strength generated from those calculated using EVPSC. Prp67Alm33, Prp59Maj41, and Prp42Maj58 are of comparable strength to each other at room temperature, which indicates that majorite substitution does not greatly affect the strength of garnets. Additionally, all three garnets are of similar strength as lower mantle phases such as bridgmanite and ferropericlase, suggesting that garnet may not be notably stronger than the surrounding lower mantle/deep upper mantle phases at the base of the upper mantle.

Zinc oxide (ZnO) is a wide band-gap semiconductor material with versatile applications in high-tech fields. Under high pressure, ZnO exhibits multiple phase transitions, which are of great significance for the development of photocatalysts, micro-devices with stress-controlled elements, and the investigation of relevant structure-activity relationships. However, previous studies have reported only theoretical calculations of its thermal transport properties under high pressure due to the challenges of experimental methodology. In this work, we employed a combination of the time-domain thermoreflectance technique and diamond anvil cell to characterize the anisotropic thermal properties of ZnO crystal under 0–20 GPa. Simultaneously, we studied the micro-structure of ZnO in the same pressure range by Raman spectra. Our proposed modified Leibfried-Schlomann equation adequately explained the non-monotonic trend of the thermal conductivity within 10 GPa observed in measurement results. Additionally, we report the ZnO thermal conductivity during the decompression process for the first time. Our experimental results and theoretical analysis advance the understanding of the thermal transport mechanism of wide-gap semiconductors under high pressure and pave the way for their high-pressure modification.

Hydrogen (H2) is the most abundant constituent in giant planets, but its thermal conductivity Λ under extreme pressure‐temperature (P‐T) conditions remains largely unknown. Here we report the Λ of H2 from ambient to 60.2 GPa at 300 K and from 300 to 773 K at 2.1 GPa. At 300 K, the Λ of liquid H2 fluctuates at ∼0.7–1.1 W m−1 K−1. Upon crystallization to H2‐I phase, the Λ jumps to 5.5 W m−1 K−1 at 7.2 GPa, and monotonically increases with pressure to ∼27 W m−1 K−1 at 60.2 GPa. Upon heating, the Λ of liquid H2 at 2.1 GPa scales with T0.68. Moreover, the density (ρ)‐dependent compressional sound velocity (Vp) of liquid and solid H2 derived from Brillouin frequency data both follow the Birch's law. Besides the novel insights into the physics of thermal transport in H2 under extreme conditions, our results significantly advance the modeling of Λ‐Vp‐ρ relationship in a planet with H2. Plain Language Summary: Hydrogen is the most abundant element in the universe and is also the major constituent in the giant plants (Jupiter, Saturn, Uranus and Neptune) in the solar system. Although most of the surface temperatures of those giant planets are colder than Earth's, their interior temperatures are actually able to reach several thousand degrees Kelvin. The heat flows within these giant planets are very active, while knowledge of heat conduction and propagation are largely unknown. This study investigates the high‐pressure thermal conductivity of H2 at room temperature and high temperature conditions. Our results show that the liquid H2 exhibits low thermal conductivity, in the range of 0.7–1.1 W m−1 K−1 at high pressures and room temperature. However, appearance of solid H2 will increase thermal conductivity significantly and reach ∼27 W m−1 K−1 at 60.2 gigapascals and room temperature. Based on our model, the low thermal conductivity of liquid H2‐He mixture may suppress the heat loss of the giant planets and explain why their surfaces are cold, but interiors are hot. Key Points: Thermal conductivity of liquid H2 varies in the range of 0.7–1.1 W m−1 K−1 at high pressures and room temperatureThermal conductivity of solid H2‐I increases from 5.5 W m−1 K−1 at 7.2 GPa to 27 W m−1 K−1 at 60.2 GPaOur model suggests that the thermal conductivity of liquid H2‐He mixture is in the range of 0.70–1.0 W m−1 K−1 at 300K [ABSTRACT FROM AUTHOR]

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 externally heated diamond-anvil cells and conducted single-crystal X-ray difraction 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 fitted to a high-temperature Birch-Murnaghan equation of state formalism, yielding bulk modulus KT0 = 21.0(4) GPa, its first pressure derivative ′KT0 = 4.45(6), dK/dT = –0.009(4) GPa/K, and thermal expansion relation αT = 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, ofering clues on the water-rich regions in Earth's deep mantle and the formation environments of those diamonds. [ABSTRACT FROM AUTHOR]

Abstract Hydrogen (H2) is the most abundant constituent in giant planets, but its thermal conductivity Λ under extreme pressure‐temperature (P‐T) conditions remains largely unknown. Here we report the Λ of H2 from ambient to 60.2 GPa at 300 K and from 300 to 773 K at 2.1 GPa. At 300 K, the Λ of liquid H2 fluctuates at ∼0.7–1.1 W m−1 K−1. Upon crystallization to H2‐I phase, the Λ jumps to 5.5 W m−1 K−1 at 7.2 GPa, and monotonically increases with pressure to ∼27 W m−1 K−1 at 60.2 GPa. Upon heating, the Λ of liquid H2 at 2.1 GPa scales with T0.68. Moreover, the density (ρ)‐dependent compressional sound velocity (Vp) of liquid and solid H2 derived from Brillouin frequency data both follow the Birch's law. Besides the novel insights into the physics of thermal transport in H2 under extreme conditions, our results significantly advance the modeling of Λ‐Vp‐ρ relationship in a planet with H2.

The high‐pressure behavior of deep carbonate dictates the state and dynamics of oxidized carbon in the Earth's mantle, playing a vital role in the global carbon cycle and potentially influencing long‐term climate change. Optical absorption and Raman spectroscopic measurements were carried out on two natural carbonate samples in diamond‐anvil cells up to 60 GPa. Mg‐substitution in high‐spin siderite FeCO3 increases the crystal field absorption band position by approximately 1000 cm–1 but such an effect is marginal at >40 GPa when entering the low‐spin state. The crystal field absorption band of dolomite cannot be recognized upon compression to 45.8 GPa at room temperature but, in contrast, the high‐pressure polymorph of dolomite exhibits a strong absorption band at frequencies higher than (Mg,Fe)CO3 in the low‐spin state by 2000–2500 cm–1. Additionally, these carbonate minerals show more complicated features for the absorption edge, decreasing with pressure and undergoing a dramatic change through the spin crossover. The optical and vibrational properties of carbonate minerals are highly correlated with iron content and spin transition, indicating that iron is preferentially partitioned into low‐spin carbonates. These results shed new light on how carbonate minerals evolve in the mantle, which is crucial to decode the deep carbon cycle. [ABSTRACT FROM AUTHOR]

The melting temperature (Tm) of iron at megabar pressures constrains the Earth's core temperature structure and dynamics. Previous experimental studies demonstrated large discrepancies in Tm at high pressures. We used the intrinsic resistance discontinuity across solid‐liquid transition as a melting criterion to study the melting behavior of iron in laser‐heated diamond anvil cells. The resistance jump is sensitive to the incipient melting, capable of detecting the emergence of less than 2 vol.% melts. We found a high melting curve of iron at 30–135 GPa, but a relatively low‐transition temperature of the slow‐fast recrystallization. The determined Tm of iron is 4306(±300) K at the core‐mantle boundary (CMB) pressure in good agreement with the static and shockwave experimental results by Anzellini et al. (2013, https://doi.org/10.1126/science.1233514) and Li et al. (2020, https://doi.org/10.1029/2020gl087758). The high melting point of iron implies a high and steep geothermal gradient and influences a heat flow across the CMB. Plain Language Summary: The melting of iron is fundamental to constrain the thermal structure, solidification, heat flux, and evolution of the Earth's core. Here, we propose a sensitive melting criterion, the resistance discontinuity across the phase transition, which is capable of detecting 2 vol.% melting of the bulk sample. Using this criterion, we determined the melting temperature of iron up to 135 GPa. The new melting curve of iron reconciles with the most recent shockwave and static experimental results, indicating a melting temperature of 4306(±300) K at the Earth's core‐mantle boundary. Large discrepancies existing in the melting of iron are unlikely caused by varying melting criteria, while chromatic aberrations should be one of the major reasons resulting from refractive optical lens in the temperature measurement system. Key Points: The criterion of an electrical resistance jump is sensitive to detect 1%–2% melt fraction of bulk iron to 135 GPa in diamond anvil cellsThe slopes in the temperature‐resistance profile are changed across the solid‐solid and slow‐fast recrystallization transitions of ironThe melting temperature of iron is ∼4306 K at core‐mantle boundary pressure, consistent with latest static and shockwave experiments [ABSTRACT FROM AUTHOR]

The kieserite-type compound cobalt(II) sulfate monohydrate, CoSO4·H2O, has been investigated under isothermal (T = 295 K) hydrostatic compression up to 10.1 GPa in a diamond anvil cell by means of single-crystal X-ray diffraction and Raman spectroscopy. The monoclinic α-phase (space group C2/c) undergoes a second-order ferroelastic phase transition at Pc = 2.40(3) GPa to a triclinic β-phase (space group P 1 ‾ $‾{1}$ ). Lattice elasticities derived from fitting third-order Birch-Murnaghan equations of state to the pressure dependent unit-cell volume data yield V0 = 354.20(6) Å3, K0 = 53.0(1.7) GPa, K′ = 5.7(1.8) for the α-phase and V0 = 355.9(8) Å3, K0 = 45.2(2.6) GPa, K′ = 6.6(6) for the β-phase. Crystal structure data of the high-pressure polymorph were determined at 2.98(6) and 4.88(6) GPa. The most obvious structural feature and thus a possible driving mechanism of the phase transition, is a partial rearrangement in the hydrogen bonding system. However, a comparative analysis of pressure-induced changes in the four kieserite-type compounds investigated to date suggests that the loss of the point symmetry 2 at the otherwise rather rigid SO4 tetrahedron, allowing symmetrically unrestricted tetrahedral rotations and edge tiltings in the β-phase, could be the actual driving mechanism of the phase transition. [ABSTRACT FROM AUTHOR]

Acoustic compressional and shear wave velocities (VP, VS) of anhydrous (AHRG) and hydrous rhyolitic glasses (HRG) containing 3.28 wt% (HRG-3) and 5.90 wt% (HRG-6) total water concentration (H[sub 2]O[sub t]) have been measured using Brillouin light scattering (BLS) spectroscopy up to 3 GPa in a diamond-anvil cell at ambient temperature. In addition, Fourier-transform infrared (FTIR) spectroscopy was used to measure the speciation of H2O in the glasses up to 3 GPa. At ambient pressure, HRG-3 contains 1.58 (6) wt% hydroxyl groups (OH-) and 1.70 (7) wt% molecular water (H2Om) while HRG-6 contains 1.67 (10) wt% OH- and 4.23 (17) wt% H2Om where the numbers in parentheses are ±1s. With increasing pressure, very little H2Om, if any, converts to OH- within uncertainties in hydrous rhyolitic glasses such that HRG-6 contains much more H2Om than HRG-3 at all experimental pressures. We observe a nonlinear relationship between high-pressure sound velocities and H2Ot, which is attributed to the distinct effects of each water species on acoustic velocities and elastic moduli of hydrous glasses. Near ambient pressure, depolymerization due to OH[sup -] reduces VS and G more than VP and KS. VP and KS in both anhydrous and hydrous glasses decrease with increasing pressure up to ~1-2 GPa before increasing with pressure. Above ~1-2 GPa, VP and KS in both hydrous glasses converge with those in AHRG. In particular, VP in HRG-6 crosses over and becomes higher than VP in AHRG. HRG-6 displays lower VS and G than HRG-3 near ambient pressure, but VS and G in these glasses converge above ~2 GPa. Our results show that hydrous rhyolitic glasses with ~2-4 wt% H2Om can be as incompressible as their anhydrous counterpart above ~1.5 GPa. The nonlinear effects of hydration on high-pressure acoustic velocities and elastic moduli of rhyolitic glasses observed here may provide some insight into the behavior of hydrous silicate melts in felsic magma chambers at depth. [ABSTRACT FROM AUTHOR]

The characteristics of hydrostatic stress conditions are discussed and compared with real experimental observations made under high pressure with a diamond-anvil cell. While fluid pressure-transmitting media give a well-defined single stress condition, solid pressure-transmitting media give a variety of stress conditions within the limit of their shear strength under high pressure. Owing to its low shear strength, solid helium would be the best choice for a pressure-transmitting medium to at least 100 GPa. However, helium is so compressible that care should be taken on minimizing irregular deformation of a gasket hole, which often causes complicated stress states. A review is given on the quasi-hydrostatic limits of solidified pressure-transmitting media, and some ways to reduce nonhydrostaticity are discussed including the case of low-temperature experiments. [ABSTRACT FROM AUTHOR]

Carbonate minerals play a dominant role in the deep carbon cycle. Determining the high-pressure and high-temperature vibrational properties of carbonates is essential to understand their anharmonicity and their thermodynamic properties under crustal and upper mantle conditions. Building on our previous study on aragonite, calcite (both CaCO3 polymorphs), dolomite [CaMg(CO3)2], magnesite (MgCO3), rhodochrosite (MnCO3), and siderite (FeCO3) (Farsang et al. 2018), we have measured the pressure- and temperature-induced frequency shifts of Raman-active vibrational modes up to 6 GPa and 500 °C for all naturally occurring aragonite- and calcite-group carbonate minerals, including cerussite (PbCO3), strontianite (SrCO3), witherite (BaCO3), gaspeite (NiCO3), otavite (CdCO3), smithsonite (ZnCO3), and spherocobaltite (CoCO3). Our Raman and XRD measurements show that cerussite decomposes to a mixture of Pb2O3 and tetragonal PbO between 225 and 250 °C, smithsonite breaks down to hexagonal ZnO between 325 and 400 °C, and gaspeite to NiO between 375 and 400 °C. Spherocobaltite breaks down between 425 and 450 °C and otavite between 375 and 400 °C. Due to their thermal stability, carbonates may serve as potential reservoirs for several metals (e.g., Co, Ni, Zn, Cd) in a range of crustal and upper mantle environments (e.g., subduction zones). We have determined the isobaric and isothermal equivalents of the mode Grüneisen parameter and the anharmonic parameter for each Raman mode and compare trends in vibrational properties as a function of pressure, temperature, and chemical composition with concomitant changes in structural properties. Finally, we use the anharmonic parameter to calculate the thermal contribution to the internal energy and entropy, as well as the isochoric and isobaric heat capacity of certain carbonates. [ABSTRACT FROM AUTHOR]

The diamond‐anvil cell (DAC) was invented 60 years ago, ushering in a new era for material sciences, extending research into the dimension of pressure. Most structural determinations and chemical research have been conducted at ambient pressure, i.e. the atmospheric pressure on Earth. However, modern experimental techniques are capable of generating pressure and temperature higher than those at the centre of Earth. Such extreme conditions can be used for obtaining unprecedented chemical compounds, but, most importantly, all fundamental phenomena can be viewed and understood from a broader perspective. This knowledge, in turn, is necessary for designing new generations of materials and applications, for example in the pharmaceutical industry or for obtaining super‐hard materials. The high‐pressure chambers in the DAC are already used for a considerable variety of experiments, such as chemical reactions, crystallizations, measurements of electric, dielectric and magnetic properties, transformations of biological materials as well as experiments on living tissue. Undoubtedly, more applications involving elevated pressure will follow. High‐pressure methods become increasingly attractive, because they can reduce the sample volume and compress the intermolecular contacts to values unattainable by other methods, many times stronger than at low temperature. The compressed materials reveal new information about intermolecular interactions and new phases of single‐ and multi‐component compounds can be obtained. At the same time, high‐pressure techniques, and particularly those of X‐ray diffraction using the DAC, have been considerably improved and many innovative developments implemented. Increasingly more equipment of in‐house laboratories, as well as the instrumentation of beamlines at synchrotrons and thermal neutron sources are dedicated to high‐pressure research. [ABSTRACT FROM AUTHOR]

Compression and decompression experiments on face-centered cubic (fcc) γʹ-Fe4N to 77 GPa at room temperature were conducted in a diamond-anvil cell with in situ X‑ray diffraction (XRD) to examine its stability under high pressure. In the investigated pressure range, γʹ-Fe4N did not show any structural transitions. However, a peak broadening was observed in the XRD patterns above 60 GPa. The obtained pressure-volume data to 60 GPa were fitted to the third-order Birch-Murnaghan equation of state (EoS), which yielded the following elastic parameters: K0 = 169 (6) GPa, K′ = 4.1 (4), with a fixed V0 = 54.95 Å at 1 bar. A quantitative Schreinemakers' web was obtained at 15–60 GPa and 300–1600 K by combining the EoS for γʹ-Fe4N with reported phase stability data at low pressures. The web indicates the existence of an invariant point at 41 GPa and 1000 K where γʹ-Fe4N, hexagonal closed-packed (hcp) ε-Fe7N3, double hexagonal closed-packed β-Fe7N3, and hcp Fe phases are stable. From the invariant point, a reaction γʹ-Fe4N = β-Fe7N3 + hcp Fe originates toward the high-pressure side, which determines the high-pressure stability of γʹ-Fe4N at 56 GPa and 300 K. Therefore, the γʹ-Fe4N phase observed in the experiments beyond this pressure must be metastable. The obtained results support the existing idea that β-Fe7N3 would be the most nitrogen-rich iron compound under core conditions. An iron carbonitride Fe7(C,N)3 found as a mantle-derived diamond inclusion implies that β-Fe7N3 and Fe7C3 may form a continuous solid solution in the mantle deeper than 1000 km depth. Diamond formation may be related to the presence of fluids in the mantle, and dehydration reactions of high-pressure hydrous phase D might have supplied free fluids in the mantle at depths greater than 1000 km. As such, the existence of Fe7(C,N)3 in diamond can be an indicator of water transportation to the deep mantle. [ABSTRACT FROM AUTHOR]

Hydroxide perovskite solid solutions along the CuxZn1−xSn(OH)6 join have been investigated at ambient conditions. Two compositions, Cu0.4Zn0.6Sn(OH)6 (cubic) and CuSn(OH)6 (tetragonal), have also been studied at pressures up to 17 GPa. In both ambient and high-pressure experiments, samples were characterised using powder X-ray diffraction. Bulk compositions between 0 ≤ XCu ≤ 0.4 are metrically cubic (space group Pn 3 ¯ ), whereas those with XCu = 0.9 and 1 produced single-phase tetragonal Cu0.9Zn0.1Sn(OH)6 and CuSn(OH)6 (space group P42/n). The products of syntheses with 0.5 ≤ XCu ≤ 0.8 contain coexisting cubic and tetragonal phases. The cubic → tetragonal transformation is rationalised in terms of being driven by local strain associated with the accumulation of Cu-rich domains in the cubic phase. The high-pressure studies of cubic Cu0.4Zn0.6Sn(OH)6 and tetragonal CuSn(OH)6 phases showed contrasting behaviour. The compression curve of the cubic phase is smooth without inflexion or discontinuity to 17 GPa. The derived bulk modulus of Cu0.4Zn0.6Sn(OH)6 is K0 = 75.8(4) GPa (K′ = 4). For CuSn(OH)6, compression data cannot be fitted by a single equation-of-state over the entire pressure range to 17 GPa, as there is a clear discontinuity between 7 and 10 GPa that corresponds to an increase in compressibility at higher pressures. Compression data for CuSn(OH)6 to 7 GPa are: K0 = 59.7(9) GPa, Ka0 = 79(2) GPa, and Kc0 = 38.0(3) GPa (K′ = 4 for all). It is shown that the strong Jahn–Teller distortion associated with the Cu(OH)6 octahedron is primarily responsible for the discontinuous and highly anisotropic compressional behaviour of the unit cell of CuSn(OH)6 hydroxide perovskite. [ABSTRACT FROM AUTHOR]

The kieserite-type ferrous sulfate FeSO 4 ∙H 2 O has been studied up to pressures of 9.2 GPa by means of X-ray diffraction, Fourier-transform infrared spectroscopy and Raman spectroscopy. The monoclinic phase undergoes a ferroelastic pressure-induced phase transitions at P c = 6.154(1) GPa with the thermodynamic character being second order. The structure solution of the high-pressure polymorph revealed a purely displacive transition with the SO 4 and FeO 6 units remaining unchanged in their topology. Birch-Murnaghan equations of state were fitted to the unit-cell volume data thus yielding V 0 = 365.23(30) ų, K 0 = 45.2(2) GPa, K′ = 6.7(1) for the C 2/ c phase and V 0 = 369.86(46) ų, K 0 = 38.5(6) GPa for the high-pressure P 1 ¯ polymorph with K′ fixed to 5.4 as derived from normalized pressure-strain analysis. The analyses of the high-pressure spectra and the structure refinements reveal changes in the hydrogen-bonding system to be the responsible driving mechanism for the phase transition. At 6.2 GPa FeSO 4 ·H 2 O undergoes a second order C 2/ c to P 1 ¯ phase transition. The phase transition is accompanied by a change in the hydrogen bond geometry and a splitting of the Fe site yielding two crystallographically independent FeO 6 polyhedra. Image 1 • Experimental high-pressure investigations on synthetic single crystal material. • X-ray diffraction with complementary vibrational spectroscopy data up to 9 GPa. • Polymorphism of kieserite-type α- and β-forms of FeSO 4 ∙H 2 O. • second order structural phase transition and isothermal equations of state. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Hydrogen transport from the surface to the deep interior and distribution in the mantle are important in the evolution and dynamics of the Earth. An aluminum oxy-hydroxide, δ-AlOOH, might influence hydrogen transport in the deep mantle because of its high stability extending to lower mantle conditions. The compressional behavior and spin states of δ-(Al,Fe3+)OOH phases were investigated with synchrotron X‑ray diffraction and Mössbauer spectroscopy under high pressure and room temperature. Pressure-volume (P-V) profiles of the δ-(Al0.908(9)57Fe0.045(1))OOH1.14(3) [Fe/(Al+Fe) = 0.047(10), δ-Fe5] and the δ-(Al0.832(5)57Fe0.117(1))OOH1.15(3) [Fe/(Al+Fe) = 0.123(2), δ-Fe12] show that these hydrous phases undergo two distinct structural transitions involving changes in hydrogen bonding environments and a high- to low-spin crossover in Fe3+. A change of axial compressibility accompanied by a transition from an ordered (P21nm) to disordered hydrogen bond (Pnnm) occurs near 10 GPa for both δ-Fe5 and δ-Fe12 samples. Through this transition, the crystallographic a and b axes become stiffer, whereas the c axis does not show such a change, as observed in pure δ-AlOOH. A volume collapse due to a transition from high- to low-spin states in the Fe3+ ions is complete below 32–40 GPa in δ-Fe5 and δ-Fe12, which is ~10 GPa lower than that reported for pure e-FeOOH. Evaluation of the Mössbauer spectra of δ-(Al0.824(10)57Fe0.126(4))OOH1.15(4) [Fe/(Al+Fe) = 0.133(3), δ-Fe13] also indicate a spin transition between 32–45 GPa. Phases in the δ-(Al,Fe)OOH solid solution with similar iron concentrations as those studied here could cause an anomalously high r/vF ratio (bulk sound velocity, defined as K / ρ) $\sqrt{\left. K/\rho \right)}$ at depths corresponding to the spin crossover region (~900 to ~1000 km depth), whereas outside the spin crossover region a low r/vF anomaly would be expected. These results suggest that the δ-(Al,Fe)OOH solid solution may play an important role in understanding the heterogeneous structure of the deep Earth. [ABSTRACT FROM AUTHOR]

High-pressure single-crystal X‑ray diffraction patterns on five synthetic Mg-Al tourmalines with near end-member compositions [dravite NaMg3Al6Si6O18(BO3)3(OH)3OH, K-dravite KMg3Al6Si6O18(BO3)3(OH)3OH, magnesio-foitite ☐(Mg2Al)Al6Si6O18(BO3)3(OH)3OH, oxy-uvite CaMg3Al6Si6O18(BO3)3(OH)3O, and olenite NaAl3Al6Si6O18(BO3)3O3OH, where o represents an X-site vacancy] were collected to 60 GPa at 300 K using a diamond-anvil cell and synchrotron radiation. No phase transitions were observed for any of the investigated compositions. The refined unit-cell parameters were used to constrain third-order Birch-Murnaghan pressure-volume equation of states with the following isothermal bulk moduli (K0 in GPa) and corresponding pressure derivatives (K0ʹ = ∂K0/∂P)T: dravite K0 = 97(6), K0ʹ = 5.0(5); K-dravite K0 = 109(4), K0ʹ = 4.3(2); oxy-uvite K0 = 110(2), K0ʹ = 4.1(1); magnesio-foitite K0 = 116(2), K0ʹ = 3.5(1); olenite K0 = 116(6), K0ʹ = 4.7(4). Each tourmaline exhibits highly anisotropic behavior under compression, with the c axis 2.8–3.6 times more compressible than the a axis at ambient conditions. This anisotropy decreases strongly with increasing pressure and the c axis is only ~14% more compressible than the a axis near 60 GPa. The octahedral Y- and Z-sites' composition exerts a primary control on tourmaline's compressibility, whereby Al content is correlated with a decrease in the c-axis compressibility and a corresponding increase in K0 and Kʹ. Contrary to expectations, the identity of the X-site-occupying ion (Na, 0 K, or Ca) does not have a demonstrable effect on tourmaline's compression curve. The presence of a fully vacant X site in magnesio-foitite results in a decrease of K0ʹ relative to the alkali and Ca tourmalines. The decrease in K0ʹ for magnesio-foitite is accounted for by an increase in compressibility along the a axis at high pressure, reflecting increased compression of tourmaline's ring structure in the presence of a vacant X site. This study highlights the utility of synthetic crystals in untangling the effect of composition on tourmaline's compression behavior. [ABSTRACT FROM AUTHOR]

Co2TiO4 spinel (Co2TiO4-Sp) was synthesized at 1573 K and room P by heating in an argon atmosphere for 72 h, and quasi-hydrostatically compressed to ~ 24 GPa using a diamond-anvil cell in conjunction with a synchrotron X-ray radiation (ambient T). We found that the Co2TiO4-Sp was stable up to ~ 21 GPa and transformed to a new phase at higher P. With some theoretical simulations, we revealed that this new phase adopted the CaMn2O4-type structure (Co2TiO4-CM), which might further transform to the CaTi2O4-type structure (Co2TiO4-CT) at ~ 35 GPa. The isothermal bulk modulus (KT) was experimentally obtained as 175.5(36) GPa for the Co2TiO4-Sp and 161(7) GPa for the Co2TiO4-CM, with its first pressure derivative K T ′ as 2.8(5) and 7.3(8), respectively. Furthermore, the KT was theoretically constrained (the GGA method) as 138(3) GPa for the Co2TiO4-CM and 196.8(14) GPa for the Co2TiO4-CT, with the K T ′ as 7.6(3) and 5.0(1), respectively. Consequently, the Co2TiO4-CM is ~ 12.3% denser than the Co2TiO4-Sp at ~ 21 GPa, whereas the Co2TiO4-CT is just ~ 0.8% denser than the Co2TiO4-CM at ~ 35 GPa. The spinel and post-spinel phase assemblages for the Co2TiO4 composition at some high T have been tentatively deduced as Co2TiO4-Sp, CoO-B1 (NaCl-type structure) + CoTiO3-Ilm (ilmenite-type structure), 2CoO-B1 + TiO2-α-PbO2 (α-PbO2-type structure), Co2TiO4-CM and Co2TiO4-CT, as P increases. [ABSTRACT FROM AUTHOR]

Fiber-based laser heating systems offer high flexibility and are increasingly used in high-pressure/high-temperature research. Previous fiber-based laser heating systems were based on lasers delivering radiation with 1-μm wavelength that show unfavorable heating characteristics for many sample materials. We report on the development and first experiments of a waveguide (fiber)-based CO 2 -laser heating system that can be used in a flexible manner for high-temperature research and for high-pressure/temperature experiments when combined with diamond-anvil cells. The waveguide-based CO 2 -laser heating system allows convenient heating of optically transparent samples without the need for adding an additional laser absorber. In a pilot experiment, the flexible heating system has been installed on a Brillouin scattering system to measure high-temperature sound-wave velocities in single-crystal MgO. The waveguide-based CO 2 -laser heating system offers perspectives for a variety of scientific applications, most importantly those that require the use of synchrotron facilities where space is limited and flexible solutions are required. [ABSTRACT FROM AUTHOR]

• Solid-Fe/liquid partition coefficients D S and D Si were determined up to 189 GPa. • The presence of Si and S decreases D S and increases D Si , respectively. • Our D S suggests smaller inner core S content with a given outer core S abundance. • The core is not the Fe-Si-S system but includes other light elements. Not only the Earth's outer core but also the inner core contains light elements, which causes reductions in density and velocity with respect to those of pure solid iron. Silicon, sulfur, and possibly hydrogen are believed to be important inner core light elements, because their partition coefficients between solid Fe and liquid, D (solid/liquid), are high (>0.7) under inner core pressures unlike other possible light elements such as oxygen and carbon. Recent experiments demonstrated that D Si is remarkably enhanced with increasing sulfur concentration in liquid at 15–21 GPa. Here we conducted solid/liquid partitioning experiments on the Fe-Si-S(-C) system up to the Earth's core pressure range of 189 GPa in a laser-heated diamond-anvil cell (DAC) and examined the effect of silicon-sulfur interaction on both D Si and D S. The results show that D S significantly diminishes with increasing the silicon content in liquid, while D Si increases with higher sulfur concentration. Based on these partitioning data, we explored the pairs of possible liquid outer core and solid inner core compositions in the Fe-Si-S±H±O system, which account for their respective seismological observations of the density and velocities. For the temperature at the inner core boundary of 5400 K, we obtained Fe + Ni + 2.7–3.0 wt% Si + 1.7 wt% S (fixed) + 0.32–0.59 wt% H + 0.05–2.5 wt% O for the outer core and Fe + Ni + 2.5–2.8 wt% Si + 0.69–0.70 wt% S + 0.23–0.43 wt% H for the inner core. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • SERS of SCN− were obtained at high pressure in the diamond anvil cell. • Three different geometries were adopted by SCN− adsorption simultaneously at high pressure. • High pressure promotes the N -bound and bridge-bound adsorption of SCN− on the surface of Ag NPs. • The appearance of N -bound adsorption and bridge-bound adsorption were forced by high pressure. • The activity of the SERS substrates can be basically restored from high pressure. Abstract The pressure-dependent C-N stretching mode, ν C-N , for thiocyanate ions adsorbed at the silver nanoparticles-aqueous interface is examined in situ by surface-enhanced Raman spectroscopy (SERS) via a commonly used diamond anvil cell in the experimental pressures range from 31 MPa to 943 MPa. The spectroscopic measurements show that three different geometries are adopted by thiocyanate ions adsorption simultaneously at high pressure. The stretching mode ν C-N of S-bound around 2120 cm−1 exists throughout the whole pressure range and the intensity of ν C-N of N -bound around 2070 cm−1 increased with the pressure. The ν C-N of bridge-bound coexist with the stretching mode ν C-N of S-bound and N -bound in the form of weak peaks around 2220 cm−1 at the pressures range from 627 MPa to 943 MPa. Current results demonstrate that high pressure promotes the N -bound and bridge-bound adsorption of thiocyanate ions on the surface of silver nanoparticles. [ABSTRACT FROM AUTHOR]

The phase transition between a face-centered cubic (fcc) and hexagonal close-packed (hcp) structures in Fe-4wt% Si alloy was examined in an internally resistive heated diamond-anvil cell (DAC) under high-pressure (P) and high-temperature (T) conditions to 71 GPa and 2000 K by in situ synchrotron X‑ray diffraction. Complementary laser-heated DAC experiments were performed in Fe-6.5wt% Si. The fcc-hcp phase transition boundaries in the Fe-Si alloys are located at higher temperatures than that in pure Fe, indicating that the addition of Si expands the hcp stability field. The dP/dT slope of the boundary of the entrant fcc phase in Fe-4wt% Si is similar to that of pure Fe, but the two-phases region is observed over a temperature range increasing with pressure, going from 50 K at 15 GPa to 150 K at 40 GPa. The triple point, where the fcc, hcp, and liquid phases coexist in Fe-4wt% Si, is placed at 90–105 GPa and 3300–3600 K with the melting curve same as in Fe is assumed. This supports the idea that the hcp phase is stable at Earth's inner core conditions. The stable structures of the inner cores of the other terrestrial planets are also discussed based on their P-T conditions relative to the triple point. In view of the reduced P-T conditions of the core of Mercury (well below the triple point), an Fe-Si alloy with a Si content up to 6.5 wt% would likely crystallize an inner core with an fcc structure. Both cores from Venus and Mars are currently believed to be totally molten. Upon secular cooling, Venus is expected to crystallize an inner core with an hcp structure, as the pressures are similar to those of the Earth's core (far beyond the triple point). Martian inner core will take an hcp or fcc structure depending on the actual Si content and temperature. [ABSTRACT FROM AUTHOR]

Highlights • Silver nanoparticles are fabricated directly on the surface of the diamond anvil as the SERS substrate. • The low detection limit of sulfite could reach up to 5 μmol/L in the diamond anvil cell. • The intensity of the two vibration modes showed good linearity under high pressure. • The SERS spectra of SO 3 2− were obtained at different pressure ranging from 54 MPa to 330 MPa. Abstract In this work, silver nanoparticles film was directly fabricated on the surface of the diamond anvil as SERS active substrate for the first time by using a simple and convenient method. With this approach, the SERS spectrum of sulfite was obtained with a detection limit of 5 μmol/L in diamond anvil cell (DAC) at ∼50 MPa. The SERS signal intensity of the two main vibration modes, ν sym S O and δ sym O S O, showed good linearity with the Na 2 SO 3 concentrations in the range from 5 to 40 μmol/L under high pressure. The linear correlation coefficients were 97.67% and 96.08%, respectively. The effects of pressure on the SERS intensity and Raman shift of the two modes were also studied. The SERS intensity dropped with the increase of pressure and the two main vibration modes shifted to high wave-number when the pressure increased in the pressures ranging from 54 MPa to 330 MPa. The experiments indicate that this method is rapid, convenient and sensitive in detecting sulfite at high pressures. It can be developed as an effect in situ method to detect sulfite in the process of high pressure reaction. [ABSTRACT FROM AUTHOR]

Planetary cores are composed mainly of Fe with minor elements such as Ni, Si, O, and S. The physical properties of Fe alloys depend on their composition. Changes in c/a ratio, center shifts, and elastic properties of Fe and Fe–Ni alloys were reported previously. However, such properties of Fe light-element alloys have not yet been extensively studied. Si is a plausible candidate as a light element in planetary cores. Therefore, we studied the electronic properties and compressional behavior of Fe-Si alloys with a hexagonal-close-packed (hcp) structure under high pressure using synchrotron Mössbauer spectroscopy (SMS) and X‑ray diffraction (XRD). Center shifts (CS) were observed at pressures of 21.4–45.3 GPa for Fe-2.8wt%Si and of 30.9–62.2 GPa for Fe-6.1wt%Si. Some of SMS and XRD measurements were performed under the same conditions using a newly developed system at the BL10XU beamline of SPring-8, which allowed simultaneous characterization of the electron information and crystal structure. Changes in the CS values were observed at 36.9 GPa in Fe-2.8wt%Si and 54.3 GPa in Fe-6.1wt%Si. The ratios of c/a in the hcp structure were measured at pressures of 21.2–49.6 GPa in Fe-2.8wt%Si and 32.9–61.4 GPa in Fe-6.1wt%Si. The c/a ratio changed at pressures of 30–45 GPa in Fe-2.8wt%Si and at 50 GPa in Fe-6.1wt%Si. Changes in the CS and c/a ratio were explained according to the electronic isostructural transition in Fe–Si alloys. In addition, the transition pressure increased with increasing Si content in metallic iron. This finding is significant as changes in seismic wave velocities due to the change in c/a ratio of Fe–Si alloys with an hcp structure might be observed if Venus has a solid inner core. [ABSTRACT FROM AUTHOR]

Diamond-anvil cell (DAC) experiments focusing on the solubility of carbonates and aqueous carbon speciation at subduction zones require pressure monitoring with sensitive, chemically inert sensors. Commonly used pressure indicators are either too insensitive or prone to contaminate pressure-transmitting media due to their increased solubility at high pressure and/or temperature (P-T). Here, the P- and T-induced frequency shifts of the Raman vibrational modes of natural crystalline carbonate minerals aragonite, calcite, dolomite, magnesite, rhodochrosite, and siderite have been calibrated for application as Raman spectroscopic P and T sensors in DACs up to 500 °C and 6 GPa. The shifts of all modes are quasi-constant over the observed P and T ranges and are generally less prominent for internal modes than for external modes. Our method provides a sensitive and robust alternative to traditional pressure calibrants, and has three principal advantages: (1) higher sensitivity (for particular Raman vibrational modes), (2) monitoring P-T-induced shifts of several modes allows even more accurate P-T determination, and (3) no contamination of pressure-transmitting media by foreign materials can occur. Additionally, the isobaric and isothermal equivalent of the Grüneisen parameter and the anharmonic parameter for each of the traced modes have been determined. [ABSTRACT FROM AUTHOR]

Abstract We investigated phase relations, mineral chemistry, and density of lunar highland anorthosite at conditions up to 125 GPa and 2000 K. We used a multi-anvil apparatus and a laser-heated diamond-anvil cell for this purpose. In-situ X-ray diffraction measurements at high pressures and composition analysis of recovered samples using an analytical transmission electron microscope showed that anorthosite consists of garnet, CaAl 4 Si 2 O 11 -rich phase (CAS phase), and SiO 2 phases in the upper mantle and the mantle transition zone. Under lower mantle conditions, these minerals transform to the assemblage of bridgmanite, Ca-perovskite, corundum, stishovite, and calcium ferrite-type aluminous phase through the decomposition of garnet and CAS phase at around 700 km depth. Anorthosite has a higher density than PREM and pyrolite in the upper mantle, while its density becomes comparable or lower under lower mantle conditions. Our results suggest that ancient anorthosite crust subducted down to the deep mantle was likely to have accumulated at 660–720 km in depth without coming back to the Earth's surface. Some portions of the anorthosite crust might have circulated continuously in the Earth's deep interior by mantle convection and potentially subducted to the bottom of the lower mantle when carried within layers of dense basaltic rocks. Graphical abstract Image 1 Highlights • We studied phase relations, chemistry, and density of lunar highland anorthosite. • Multianvil apparatus/laser-heated diamond anvil cell experiments were conducted. • Results suggest that ancient anorthosite crust subducted into the lower mantle. • Some portions of anorthosite might have subducted to the bottom of the mantle. [ABSTRACT FROM AUTHOR]

ThO2 is an important material for understanding the heat budget of Earth’s mantle, as well as the stability of nuclear fuels at extreme conditions. We measured the in situ high-pressure, high-temperature phase behavior of ThO2 to ~60 GPa and ~2500 K. It undergoes a transition from the cubic fluorite-type structure (thorianite) to the orthorhombic α-PbCl2 cotunnite-type structure between 20 and 30 GPa at room temperature. Prior to the transition at room temperature, an increase in unit-cell volume is observed, which we interpret as anion sub-lattice disorder or pre-transformation “melting” (Boulfelfel et al. 2006). The thermal equation of state parameters for both thorianite [V0 = 26.379(7), K0 = 204(2), αKT = 0.0035(3)] and the high-pressure cotunnite-type phase [V0 = 24.75(6), K0 = 190(3), αKT = 0.0037(4)] are reported, holding K 0 ′ $\begin{array}{} K_0^{'} \end{array} $ fixed at 4. The similarity of these parameters suggests that the two phases behave similarly within the deep Earth. The lattice parameter ratios for the cotunnite-type phase change significantly with pressure, suggesting a different structure is stable at higher pressure. [ABSTRACT FROM AUTHOR]

The phase relations, mineral chemistry and density of KREEP basalt were investigated at pressures of 12–125 GPa and temperatures up to 2810 K by a combination of large volume multi-anvil press experiments and in situ synchrotron X-ray diffraction measurements in a laser-heated diamond anvil cell. Our results showed that grossular-rich majorite garnet, liebermannite and Al-bearing stishovite are dominant in the upper-to-middle part of the upper mantle while in the lowermost transition zone a dense Ti-rich CaSiO 3 perovskite exsoluted from the garnet, which becomes more pyropic with increasing pressure. At lower mantle conditions, these minerals transform into an assemblage of bridgmanite, Ca-perovskite, Al-stishovite, the new aluminium-rich (NAL) phase and the calcium-ferrite type (CF) phase. At pressures higher than 50 GPa, NAL phase completely dissolved into the CF phase, which becomes the main deposit of alkali metals in the lower mantle. The density of KREEP estimated from phase compositions obtained by energy dispersive X-ray spectroscopy (EDS) in scanning (SEM) and transmission (TEM) electron microscopes, was found substantially denser than pyrolite suggesting that the Earth primordial crust likely subducted deep into the Earth’s mantle after or slightly before the final solidification of magma ocean at 4.53 Ga. Radiogenic elements U, Th and 40 K which were abundant in the final residue of magma ocean were brought down along the subduction of the primordial crust and generate heat by decay after the settlement of the primordial crust on top of the CMB, suggesting the non-homogeneous distribution of radiogenic elements in the Hadean mantle with implications for the thermal history of the Earth. [ABSTRACT FROM AUTHOR]

In situ surface enhanced Raman scattering (SERS) in solution was tested in this study at ambient temperature and high pressure (up to 978 MPa) in a diamond-anvil cell, with the intent of resolving trace detection in high pressure conditions. The 4-chlorothiophenol solution was used as the analyte in our experiments. A silver nanoparticle layer, formed by chemical reduction and assembled on a poly (allylamine hydrochloride)-modified silicon wafer, was used as the substrate. There was an obvious rise in SERS intensity when the sample chamber was pressurized for the first time in the diamond-anvil cell. But then the intensity drop occurred with increasing pressure and all peaks have pressure-induced blue shift below 700 MPa. The SERS intensity and Raman shift displayed irregular changes in the pressure range from 700 MPa to 978 MPa. The discovery of the survival of in situ high-pressure SERS in solution in the present study may make it a prospecting tool for the high-precision detection of analyte in high pressure conditions. Moreover, it could provide more information on the SERS mechanisms that have been puzzling us for decades. [ABSTRACT FROM AUTHOR]

A quantitative knowledge of the equation of state of wadsleyite solid solutions is needed to refine thermodynamic and thermoelastic models for the transition zone in Earth's upper mantle. Here we present the results of high-pressure single-crystal X-ray diffraction experiments on two crystals of slightly hydrous iron-bearing wadsleyite with Fe/(Mg+Fe) = 0.112(2), Fe3+/ΣFe = 0.15(3), and 0.24(2) wt% H²O up to 20 GPa. By compressing two wadsleyite crystal sections inside the same diamond-anvil cell, we find a negligible influence of crystal orientation on the derived equation of state parameters. Volume and linear compression curves were analyzed with finite strain theory to demonstrate their mutual consistency for the Reuss bound indicating quasi-hydrostatic stress conditions. The results on the here-studied wadsleyite crystals are incorporated into a multi-end-member model to describe the equation of state for wadsleyite solid solutions in the system Mg2SiO4-Fe2 SiO4-MgH2SiO4-Fe3O4. For the hypothetical ferrous wadsleyite end-member, Fe2SiO4, we find a substantially larger bulk modulus than expected by extrapolating currently accepted trends. The multi-end-member equation of state model may serve as a basis for the calculation of phase equilibria and the interpretation of seismic observations regarding the transition zone. [ABSTRACT FROM AUTHOR]

The spin states of iron in deep magmas are one of the most important properties that affect the partitioning of iron between magmas and minerals and, thus, the gravitational stability of magmas in the Earth. We investigated the spin state and electronic environments of iron in a basaltic glass containing ~70 Fe¹+/ΣFe at room temperature and pressures from 1 bar to 130 GPa using a diamond-anvil cell combined with energy domain synchrotron 57Fe Mössbauer source spectroscopy. The basaltic glass represents an analog of a multi-component magma typical for the Earth. The Mössbauer spectra could be fitted by a two pseudo-Voigt doublet model including a high quadrupole splitting (QS) doublet and a low QS doublet, which were assigned to high-spin Fe2+ and high-spin Fe3+, respectively. The high-spin states of Fe2+ and Fe3+ remained up to 130 GPa corresponding to the pressure in the lowermost mantle. The center shift values of high-spin Fe2+ and Fe3+ did not show large changes with pressure, ruling out sharp electronic changes in the basaltic glass. Therefore, a sharp and complete spin crossover of Fe2+ from the high-spin to the low-spin state does not appear to occur in the basaltic glass although the possibility of a partial spin transition cannot be fully excluded. The QS values of Fe2+ increased slightly at 0-20 GPa and above 100 GPa, and the higher value was preserved after decompression to ambient conditions. This behavior may be related to distortion of Fe2+ polyhedra due to short-range ordering on compression. Such a distortion of Fe2+ polyhedra could gradually stabilize Fe2+ in the basaltic glass with pressure compared to bridgmanite according to the Jahn-Teller effect, and thus could gradually enhance the partitioning of iron into deep magmas in the lower mantle. [ABSTRACT FROM AUTHOR]

Density and structural changes of matter in their liquid or amorphous form, such as silicates melts, molecular fluids, or glasses, are of extreme importance to model the interior of planetary bodies. However, measuring the evolution of amorphous materials under extreme conditions of pressure and temperature remains challenging mainly because of the sample dimensions and the weak interaction with X-ray probes. This contribution highlights recent developments to measure the density of amorphous material, mainly silicate glasses made of light elements, to high pressure conditions. In particular, the X-ray absorption method at synchrotron sources is discussed as a new opportunity for high pressure experiments on glasses, fluids, and melts. Recent achievements using X-ray Raman scattering spectroscopy to obtain data on the local electronic environment of the main constituents of silicate glasses at high pressure are also presented. Finally, perspectives of these recent developments are discussed as well as their potential for high pressure research in the next years. [ABSTRACT FROM PUBLISHER]

We present a method to perform improved measurements of the effects of chemical variability on physical properties of single-crystal samples in the diamond-anvil cell by employing a multi-sample approach. By customizing the sizes and shapes of the samples using a focused ion beam machine the simultaneous loading of relatively large crystals into a single sample chamber becomes feasible. To illustrate the potential of this approach, elastic properties of four single crystals of ringwoodite with different chemical compositions have been measured at high pressure. Our results suggest that the multi-sample approach allows for the quantification of small effects of chemical variations, such as iron and hydrogen incorporation, on physical properties. Furthermore, we discuss the possibility of using the multi-sample approach to load several crystals with different crystallographic orientations of the same material into one sample chamber in order to map out the direction dependence of anisotropic physical properties. [ABSTRACT FROM PUBLISHER]

Iron- and aluminum-bearing MgSiO3 bridgmanite is the most abundant mineral in the Earth's interior; hence its crystal chemistry is fundamental to expanding our knowledge of the deep Earth and its evolution. In this study, the valence and spin state of iron in well-characterized Al-free Fe3+-rich bridgmanite were investigated by means of Mössbauer spectroscopy to understand the effect of ferric iron on the spin state. We found that a minor amount of Fe3+ is in the low-spin state above 36 GPa and that its proportion does not increase substantially with pressure up to 83 GPa. This observation is consistent with recent experimental studies that used Mössbauer and X-ray emission spectroscopy. In the Earth's deep lower mantle, Fe3+ spin crossover may take place at depths below 900 and 1200 km in pyrolite and MORB, respectively. However, the effect of spin crossover on physical properties may be small due to the limited amount of Fe3+ in the low-spin state. [ABSTRACT FROM AUTHOR]

Melting experiments were performed on the Fe–Fe 3 S system at high pressures between 34 and 254 GPa in a laser-heated diamond-anvil cell (DAC), using starting materials of fine-grained homogeneous mixtures of Fe and FeS (<500 nm) prepared by induction melting and rapid quenching techniques. Melting phase relations including the liquid/solid partitioning of sulfur were examined on the basis of textural and chemical characterizations of recovered samples using a focused ion beam (FIB) and electron microprobes. The results demonstrate that the sulfur content in eutectic liquid decreases substantially with increasing pressure. The eutectic liquid Fe with 5.7 ( ± 0.3 ) wt.% S coexisted with both solid Fe 3 S and Fe containing 3.9 ( ± 0.4 ) wt.% S at 254 GPa and 3550 K. The eutectic liquid at inner core boundary (ICB) pressure includes less sulfur than is required to account for the density deficit of the outer core (≥10 wt.% S). Furthermore, the difference in sulfur concentration between coexisting liquid and solid is not sufficient to account for the observed density jump across the ICB. These indicate that sulfur cannot be a predominant light element in the core. [ABSTRACT FROM AUTHOR]

ZnTiO spinel (ZnTiO-Sp) was synthesized by a solid-state reaction method (1573 K, room P and 72 h) and quasi-hydrostatically compressed to ~24 GPa using a DAC coupled with a synchrotron X-ray radiation (ambient T). We found that the ZnTiO-Sp was stable up to ~21 GPa and transformed to another phase at higher P. With some theoretical simulations, we revealed that this high- P phase adopted the CaTiO-type structure (ZnTiO-CT). Additionally, the isothermal bulk modulus ( K ) of the ZnTiO-Sp was experimentally obtained as 156.0(44) GPa and theoretically obtained as 159.1(4) GPa, with its first pressure derivative $$K_{\text{T}}^{'}$$ as 3.8(6) and 4.37(4), respectively. The volumetric and axial isothermal bulk moduli of the ZnTiO-CT were theoretically obtained as K = 150(2) GPa ( $$K_{\text{T}}^{'}$$ = 5.4(2); for the volume), K = 173(2) GPa ( $$K_{{\text{T-}}a}^{'}$$ = 3.9(1); for the a-axis), K = 74(2) GPa ( $$K_{{\text{T-}}b}^{'}$$ = 7.0(2); for the b-axis), and K = 365(8) GPa ( $$K_{{\text{T-}}c}^{'}$$ = 1.5(4); for the c-axis), indicating a strong elastic anisotropy. The ZnTiO-CT was found as ~10.0 % denser than the ZnTiO-Sp at ambient conditions. The spinel and post-spinel phase assemblages for the ZnTiO composition at high T have been deduced as ZnTiO-Sp, ZnTiO-ilmenite + ZnO-wurtzite, ZnTiO-ilmenite + ZnO-rock salt, ZnTiO-perovskite + ZnO-rock salt, and ZnTiO-CT as P increases, which presumably implies a potential stability field for a CT-type MgSiO at very high P. [ABSTRACT FROM AUTHOR]

The thermal conductivity of the Earth's core can be estimated from its electrical resistivity via the Wiedemann–Franz law. However, previously reported resistivity values are rather scattered, mainly due to the lack of knowledge with regard to resistivity saturation (violations of the Bloch–Grüneisen law and the Matthiessen's rule). Here we conducted high-pressure experiments and first-principles calculations in order to clarify the relationship between the resistivity saturation and the impurity resistivity of substitutional silicon in hexagonal-close-packed (hcp) iron. We measured the electrical resistivity of Fe–Si alloys (iron with 1, 2, 4, 6.5, and 9 wt.% silicon) using four-terminal method in a diamond-anvil cell up to 90 GPa at 300 K. We also computed the electronic band structure of substitutionally disordered hcp Fe–Si and Fe–Ni alloy systems by means of Korringa–Kohn–Rostoker method with coherent potential approximation (KKR-CPA). The electrical resistivity was then calculated from the Kubo–Greenwood formula. These experimental and theoretical results show excellent agreement with each other, and the first principles results show the saturation behavior at high silicon concentration. We further calculated the resistivity of Fe–Ni–Si ternary alloys and found the violation of the Matthiessen's rule as a consequence of the resistivity saturation. Such resistivity saturation has important implications for core dynamics. The saturation effect places the upper limit of the resistivity, resulting in that the total resistivity value has almost no temperature dependence. As a consequence, the core thermal conductivity has a lower bound and exhibits a linear temperature dependence. We predict the electrical resistivity at the top of the Earth's core to be 1.12 × 10 − 6 Ω m , which corresponds to the thermal conductivity of 87.1 W/m/K. Such high thermal conductivity suggests high isentropic heat flow, leading to young inner core age (<0.85 Gyr old) and high initial core temperature. It also strongly suppresses thermal convection in the core, which results in no convective motion in inner core and possibly thermally stratified layer in the outer core. [ABSTRACT FROM AUTHOR]

We describe the experimental protocols necessary to measure the crystal structures of minerals trapped within diamonds by single-crystal X-ray diffraction to the same quality as obtained from minerals studied at ambient conditions. The results show that corrections for X-ray absorption in complex cases can be made with good precision. Comparison of the refined structure of a single-crystal olivine inclusion inside a diamond with the structure of a similar olivine held in a high-pressure diamond-anvil cell shows that data resolution, not the correction for absorption effects, is the dominant factor in influencing the quality of structures determined at high pressures by single-crystal X-ray diffraction. [ABSTRACT FROM AUTHOR]

The crystal structure and equation of state of coesite (space group C2/c) and its high-pressure polymorph coesite-II (space group P21/n) under pressure have been studied using X-ray powder diffraction in a diamond-anvil cell (DAC) up to 31 GPa at room-temperature and first-principles calculations at 0 K up to 45 GPa. New diffraction peaks appear above 20 GPa, indicating the formation of coesite-II structure. The calculated enthalpies provide theoretical support for the pressure-induced phase transformation from coesite to coesite-II at ~21.4 GPa. Compared with coesite, the coesite-II structure is characterized by a "doubled" b-axis and the breakdown of the linear Si1-O1-Si1 angle in coesite into two distinct angles-one is ~176°, close to linear, whereas the other decreases by 22 to 158°. Coesite is very anisotropic with the a-axis the shortest and twice more compressible than the b- and c-axis. By comparison, coesite-II is not so anisotropic with similar compressibilities in its a-, b-, and c-axis. As analyzed by a third-order Eulerian finite strain equation of state, the bulk modulus of coesite at 21.4 GPa is 182.3 GPa, and that of coesite-II is 140.8 GPa, indicating that coesite-II is much more compressible than coesite. The existence of coesite-II in the coldest subduction zone will change the elasticity and anisotropic properties of the subducting materials dramatically. [ABSTRACT FROM AUTHOR]