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Current anvil designs and problems associated with various efforts to generate static high pressures beyond the limit of conventional diamond anvil cells (DACs) (∼400 GPa) are reviewed. Pressures o...

Both micro-paired and conical support type double-stage diamond anvil cells (ds-DAC) were tested using a newly synthesized ultra-fine nano-polycrystalline diamond (NPD). Well-focused X-ray sub-micr...

The high-pressure behavior of the natural MTN-type clathrasil chibaite was investigated with in situ single-crystal X-ray diffraction and Raman spectroscopy under hydrostatic pressures up to 10.3 GPa. The experiments were conducted in diamond-anvil cells using 4:1 methanol-ethanol mixture (ME), helium (He) and neon (Ne) as pressure-transmitting media. The pressure dependent unit-cell volumes of the room-pressure polymorph yield an isothermal bulk modulus KT0 = 25.75 (19) GPa for the compression in the non-penetrating ME fluid. Due to the penetration of the Ne and He atoms into the cages of the framework, the crystal structure is significantly stiffened resulting in KT0 = 42.5 (1.2) GPa (Ne) and KT0 = 58 (2) GPa (He). Under the influence of pressure both the evolution of the Raman spectra and the change in cell metrics indicate a distortion of the lattice without leading to a complete pressure-induced amorphization, as observed for many comparable porous structures. Compressed in the non-penetrating ME, the cubic F d 3 ¯ m framework of chibaite undergoes a first transformation step in the pressure range between 1.7 GPa and 2.2 GPa and a second one between 3.9 GPa and 4.3 GPa. The accompanied formation of crystal domains did not allow a reliable determination of the distorted crystal structures. The unit-cell parameters might suggest a monoclinic metric for pressures >1.7 GPa and a monoclinic or tetragonal metric for pressures >3.9 GPa. However, in some samples even the co-existence of crystal domains of a different degree of lattice distortions has been proved.

Making and breaking bonds in a solid-state compound greatly influences physical properties. A well-known playground for such bonding manipulation is the ThCr

We have developed a double stage diamond anvil cell (ds-DAC) technique for reproducible pressure by precisely fabricating 2nd stage anvils using a focused ion beam system. We used 2nd stage micro-a...

In the bulk silicate Earth, chlorine is more depleted than other elements with similar volatilities; however, the cause of terrestrial chlorine depletion is not well understood. Two major hypotheses have been proposed to explain this depletion: Incorporation into the Earth's metallic core and escape to space. The former hypothesis can be tested by investigating the partitioning of chlorine between iron-rich metallic liquids and silicate melts. In this study, we investigated the experimental partitioning of chlorine between iron-rich metallic liquids and silicate melts at pressures from 4 to 23 GPa and temperatures from 1,650 to 2,400°C using multi-anvil presses. The results demonstrate that chlorine is moderately to highly lithophile under the experimental conditions. In sulfur-free experiments, chlorine becomes slightly more siderophile as temperature increases and less siderophile as pressure increases. For sulfur-bearing experiments, no significant effects of pressure or temperature were observed. Based on these data and thermodynamic considerations, we obtained empirical laws to estimate chlorine partition coefficients between iron-rich metallic liquids and silicate melts. Under the P-T conditions that would have controlled metal-silicate equilibration during core segregation in the Earth, the calculated metal-silicate partition coefficients for chlorine are much lower than unity. This result suggests that terrestrial chlorine that may have been present in the accreting Earth was not partitioned into its core, supporting that escape to space is the more likely hypothesis. If terrestrial chlorine was lost to space, chlorine depletion may have resulted from the loss of the primordial hydrosphere during the formation of the Earth.

We have measured the volumes of dhcp- and fcc-FeH x at temperatures of 300–950 K and hydrogen pressures of 4–7 GPa using in situ X-ray diffraction. For fcc-FeH x , the expanded volumes per Fe atom with respect to fcc-Fe metal were converted to hydrogen compositions x using hydrogen-induced volume expansion v H . A miscibility gap in the x – T diagram of fcc-FeH x was confirmed to be in agreement with an earlier study, and the critical pressure was located in a rather narrow span of 4.0–4.5 GPa with a critical composition of x = ∼0.4. We examined Arrhenius plot analysis of the x – T relations to derive the enthalpy of solution of hydrogen ΔH s . However, an irregular behavior of the x – T relations did not allow derivation of a reliable value of ΔH s .

Density of the Earth's core is lower than that of pure iron and the light element(s) in the core is a long-standing problem. Hydrogen is the most abundant element in the solar system and thus one of the important candidates. However, the dissolution process of hydrogen into iron remained unclear. Here we carry out high-pressure and high-temperature in situ neutron diffraction experiments and clarify that when the mixture of iron and hydrous minerals are heated, iron is hydrogenized soon after the hydrous mineral is dehydrated. This implies that early in the Earth's evolution, as the accumulated primordial material became hotter, the dissolution of hydrogen into iron occurred before any other materials melted. This suggests that hydrogen is likely the first light element dissolved into iron during the Earth's evolution and it may affect the behaviour of the other light elements in the later processes., The Earth's core has lower density than pure iron and many studies have looked into which light elements may be present. The authors here carry out in situ high pressure and temperature neutron experiments indicating that hydrogen may have been the first light element to dissolve into the iron core.

Stability and phase relations of coexisting enstatite and H2 fluid were investigated in the pressure and temperature regions of 3.1–13.9 GPa and 1500–2000 K using laser-heated diamond-anvil cells. XRD measurements showed decomposition of enstatite upon heating to form forsterite, periclase, and coesite/stishovite. In the recovered samples, SiO2 grains were found at the margin of the heating hot spot, suggesting that the SiO2 component dissolved in the H2 fluid during heating, then precipitated when its solubility decreased with decreasing temperature. Raman and infrared spectra of the coexisting fluid phase revealed that SiH4 and H2O molecules formed through the reaction between dissolved SiO2 and H2. In contrast, forsterite and periclase crystals were found within the hot spot, which were assumed to have replaced the initial orthoenstatite crystals without dissolution. Preferential dissolution of SiO2 components of enstatite in H2 fluid, as well as that observed in the forsterite H2 system and the quartz H2 system, implies that H2-rich fluid enhances Mg/Si fractionation between the fluid and solid phases of mantle minerals.

High-pressure responses of RbHCO3 and CsHCO3 were characterized by in situ Raman spectroscopy and X-ray and neutron diffraction observations. RbHCO3 exhibited a monoclinic (phase IV) and a triclinic (phase V) high-pressure phase at ~0.5 ​GPa and room temperature. Increasing compression induced unique behavior in a specific cell parameter (a in phase IV or c in phase V), which first increased, and then decreased at ~1 ​GPa, likely owing to the rearrangement of Rb+ and reconfiguration of the ordered (HCO3−)2 dimers. Deuterium positions in phase IV of RbDCO3 were determined. The hydrogen bonding remained moderately strong, and possibly did not affect the phase transition despite the accompanying disordering and ordering of the dimers. CsHCO3 showed no structural change up to 5 ​GPa, suggesting that its ambient phase (isostructural to phase IV of KHCO3) was already stable at high pressure. The structural stability appeared to be systematically related to the cation size.

The natural sII-type clathrasil chibaite [chemical formula SiO2·(M12,M16), whereMxdenotes a guest molecule] was investigated using single-crystal X-ray diffraction and Raman spectroscopy in the temperature range from 273 to 83 K. The O atoms of the structure at room temperature, which globally conforms to space group Fd{\overline 3}m [V= 7348.9 (17) Å3,a= 19.4420 (15) Å], have anomalous anisotropic displacement parameters indicating a static or dynamic disorder. With decreasing temperature, the crystal structure shows a continuous symmetry-lowering transformation accompanied by twinning. The intensities of weak superstructure reflections increase as temperature decreases. A monoclinic twinned superstructure was derived at 100 K [A2/n,V= 7251.0 (17) Å3,a′ = 23.7054 (2),b′ = 13.6861 (11),c′ = 23.7051 (2) Å, β′ = 109.47°]. The transformation matrix from the cubic to the monoclinic system isai′ = (½ 1 ½ / ½ 0 −½ / ½ −1 ½). TheA2/nhost framework has Si—O bond lengths and Si—O—Si angles that are much closer to known values for stable silicate-framework structures compared with the averaged Fd{\overline 3}m model. As suggested from band splitting observed in the Raman spectra, the [512]-type cages (one crystallographically unique in Fd{\overline 3}m, four different inA2/n) entrap the hydrocarbon species (CH4, C2H6, C3H8,i-C4H10). The [51264]-type cage was found to be unique in both structure types. It contains the larger hydrocarbon molecules C2H6, C3H8andi-C4H10.

Ultrafine-grained (0.2–0.3 µm) WC–Ni hardmetals with a low Ni content (3–5 wt%) were developed using new production techniques based on adding an appropriate amount of VC and Cr3C2, combined with the strong mixing of raw materials. Their uniaxial compressibility was subsequently compared with that of existing WC–Ni and WC–Co hardmetals to assess their suitability for use as anvils in various high pressure experiments, particularly those associated with neutron or magnetic studies. The ultimate compressive strength of the newly developed hardmetals was over 7.7 GPa, which was higher by 1.2 GPa than that of the existing WC–Ni hardmetal ‘MF10’. When these hardmetals were used as anvils, a pressure of approximately 16 GPa was generated using a Paris-Edinburgh-type apparatus with φ8 mm culet, thereby proving that they can allow the physical properties of various materials to be measured at higher pressures than is possible with existing hardmetals.

X-ray radiography was applied to observe the segregation process of iron from silicate at high pressure and high temperature in mixtures containing light elements. As the temperature of the hydrogen-containing sample increases, the molten iron becomes coherent. Small droplets of iron sink to the bottom of the chamber, where they merge into a single, large droplet. The small iron droplets exhibit complex motion, moving in random directions. Markedly different behavior is found in the sulfur-containing sample, where no clear motion of the molten iron is observed. Instead, as the sample temperature is increased, the concentration of iron near the wall of the sample chamber gradually increases. These observations demonstrate that the behavior of molten iron changes according to the dissolved elements. This X-ray radiography experiment represents a powerful technique to study the segregation process of molten iron from solid or partially molten silicate, particularly when combined with high-resolution tomograp...

PLANET is a time-of-flight (ToF) neutron beamline dedicated to high-pressure and high-temperature experiments. The large six-axis multi-anvil high-pressure press designed for ToF neutron diffraction experiments enables routine data collection at high pressures and high temperatures up to 10 GPa and 2000 K, respectively. To obtain clean data, the beamline is equipped with the incident slits and receiving collimators to eliminate parasitic scattering from the high-pressure cell assembly. The high performance of the diffractometer for the resolution (Δ d / d ~0.6%) and the accessible d -spacing range (0.2–8.4 A) together with low-parasitic scattering characteristics enables precise structure determination of crystals and liquids under high pressure and temperature conditions.

A post-cotunnite phase transition in zirconia (ZrO2) at high pressure was investigated by synchrotron X-ray diffraction measurements and ab initio calculations based on density functional theory. This study successfully demonstrated a cotunnite- to Fe2P-type phase transition. Static enthalpy difference (ΔH) calculations predicted the appearance of the Fe2P phase at 124 GPa (LDA) and 143 GPa (GGA), and experimental trials demonstrated the coexistence of the Fe2P and cotunnite phases at 175 GPa after heating to 3,000 K. Both phases were quenchable to ambient conditions. The volume of the Fe2P phase was slightly less (~Δ 0.6 %) than that of the cotunnite phase over the experimental pressure range, indicating that the Fe2P phase is the higher pressure phase. The coexistence of both phases in this study may be attributed to the slow kinetics of the phase transition resulting from the close structural relationship of the two phases. An Fe2P-type structural model can be derived by applying a simple operation to the cotunnite-type structure, consisting of a 1/2 shift of several zirconium arrangements parallel to the b-axis of the cotunnite-type unit cell. It is concluded that the high-pressure cotunnite-to-Fe2P phase transition may be a common trend in many dioxides.

In situ neutron diffraction measurements combined with the pulsed neutron source at the Japan Proton Accelerator Research Complex (J-PARC) were conducted on high-pressure polymorphs of deuterated portlandite (Ca(OD) 2 ) using a Paris–Edinburgh cell and a multi-anvil press. The atomic positions including hydrogen for the unquenchable high-pressure phase at room temperature (phase II′) were first clarified. The bent hydrogen bonds under high pressure were consistent with results from Raman spectroscopy. The structure of the high-pressure and high-temperature phase (Phase II) was concordant with that observed previously by another group for a recovered sample. The observations elucidate the phase transition mechanism among the polymorphs, which involves the sliding of CaO polyhedral layers, position modulations of Ca atoms, and recombination of Ca–O bonds accompanied by the reorientation of hydrogen to form more stable hydrogen bonds.

In contrast to conventional ceramic ionic conductors relying on bulk ionic transport, making use of interfaces such as grain boundary and surface may provide various new possibilities to develop novel ionic conductors. Here we demonstrate that nanograined structures of yttria-doped zirconia (YSZ), of which the bulk property involves negligible proton solubility or conductivity, are endowed with appreciable proton conductivity via interfacial hydrated layers. A combination of nanopowder synthesis and ultra high-pressure compaction (4 GPa) at room temperature enables us to fabricate the nanograined specimens. The material thus prepared can retain an appreciable amount of protons and water within the grain-boundary or “internal surface”, resulting in a hierarchical structure of hydroxyl groups and water molecules with different thermal stability and thereby mobility. The physicochemical properties of those protonic species have been investigated by means of in situ FT-IR, 1H MAS NMR, and thermal desorption s...

High-pressure phase transformations between the polymorphic forms I, II, III, and IIIb of CaCO3 were investigated by analytical in situ high-pressure high-temperature experiments on oriented single-crystal samples. All experiments at non-ambient conditions were carried out by means of Raman scattering, X-ray, and synchrotron diffraction techniques using diamond-anvil cells in the pressure range up to 6.5 GPa. The composite-gasket resistive heating technique was applied for all high-pressure investigations at temperatures up to 550 K. High-pressure Raman spectra reveal distinguishable characteristic spectral differences located in the wave number range of external modes with the occurrence of band splitting and shoulders due to subtle symmetry changes. Constraints from in situ observations suggest a stability field of CaCO3-IIIb at relatively low temperatures adjacent to the calcite-II field. Isothermal compression of calcite provides the sequence from I to II, IIIb, and finally, III, with all transformations showing volume discontinuities. Re-transformation at decreasing pressure from III oversteps the stability field of IIIb and demonstrates the pathway of pressure changes to determine the transition sequence. Clausius–Clapeyron slopes of the phase boundary lines were determined as: ΔP/ΔT = −2.79 ± 0.28 × 10−3 GPa K−1 (I–II); +1.87 ± 0.31 × 10−3 GPa K−1 (II/III); +4.01 ± 0.5 × 10−3 GPa K−1 (II/IIIb); −33.9 ± 0.4 × 10−3 GPa K−1 (IIIb/III). The triple point between phases II, IIIb, and III was determined by intersection and is located at 2.01(7) GPa/338(5) K. The pathway of transition from I over II to IIIb can be interpreted by displacement with small shear involved (by 2.9° on I/II and by 8.2° on II/IIIb). The former triad of calcite-I corresponds to the [20-1] direction in the P21/c unit cell of phase II and to [101] in the pseudomonoclinic C $${\bar{1}}$$ setting of phase IIIb. Crystal structure investigations of triclinic CaCO3-III at non-ambient pressure–temperature conditions confirm the reported structure, and the small changes associated with the variation in P and T explain the broad stability of this structure with respect to variations in P and T. PVT equation of state parameters was determined from experimental data points in the range of 2.20–6.50 GPa at 298–405 K providing $$K_{{{\text{T}}_{0} }}$$ = 87.5(5.1) GPa, (δK T/δT) P = −0.21(0.23) GPa K−1, α 0 = 0.8(21.4) × 10−5 K−1, and α 1 = 1.0(3.7) × 10−7 K−1 using a second-order Birch–Murnaghan equation of state formalism.

Species dissolved in H 2 fluid were investigated in a SiO 2 –H 2 system. Raman and infrared (IR) spectra were measured at high pressure and room temperature after heating experiments were conducted at two pressure and temperature conditions: 2.0 GPa, 1700 K and 3.0 GPa, 1500 K. With the dissolution of quartz, a SiH vibration mode assignable to SiH 4 was detected from Raman spectra of the fluid phase. Furthermore, an OH vibration mode was observed at 3260 cm −1 from the IR spectra at 3.0 GPa. With decreasing pressure, the OH vibration frequencies observed between 3.0 and 2.1 GPa correspond to that of ice VII, and those observed at 1.4 and 1.1 GPa correspond to that of ice VI. These results indicate that the chemical reaction between dissolved SiO 2 components and H 2 fluid caused the formation of H 2 O and SiH 4 , which was contrastive to that observed in SiO 2 –H 2 O fluid. Results imply that a part of H 2 is oxidized to form H 2 O when SiO 2 components of mantle minerals dissolve in H 2 fluid, even in an iron-free system.

Lawsonite is considered to be one of the most likely hydrous minerals to explain the persistence of seismic low-velocity layers (LVLs) atop subducted slabs to depths of 100–250 km due mainly to the fact that it can persist to these depths, in contrast to other hydrous minerals such as antigorite. However, as it is highly anisotropic and subjected to intense deformation during subduction, further constrains on the development of lawsonite crystal preferred orientation (CPO) at high pressure and temperature are required in order to evaluate its role in slowing seismic waves. We have deformed lawsonite aggregates at 5 GPa and 500–800 °C corresponding to 150 km depth and covering temperatures for both cold and hot subduction zones. In this study, we report a new lawsonite CPO pattern resulting from dislocation creep deformation that has not been previously observed. The [100] axes concentrate into the shear direction and the [010] axes are normal to the shear plane, respectively (we refer to this as “type-1” CPO). Such CPO is consistent with our transmission electron microscope (TEM) observations identifying (010)[100] as a dominant dislocation slip-system. The seismic properties resulting from this CPO show the fast P-wave direction to be parallel to the shear direction, and the slow P-wave direction and maximum S-wave anisotropy normal to the shear plane. We performed calculation of omphacite-lawsonite aggregates using our experimental data and varied both the lawsonite contents and the slab dipping angle. Our results show that a reasonable amount of lawsonite can explain Vs reduction in the LVLs, but cannot explain the Vp reduction. However, the presence of lawsonite would induce a rotation of the fast S-wave polarization toward the trench direction as the S-wave anisotropy increases or decreases according to the lawsonite proportion, its CPO strength and the slab dipping angle. We believe that our calculation can now be used for investigation of lawsonite effect in various subductions zones.

High-pressure behaviors of Linde-type A (LTA) zeolite were investigated using a quasi-hydrostatic pressure medium of noble gases (helium or argon). High-pressure in situ X-ray diffraction measurements combined with the use of a diamond anvil cell did not observe any structural phase transition for LTA zeolites up to a pressure of approximately 12 GPa at room temperature. However, it was found that the compressibility strongly depended not only on the pressure medium but also on the pressurization process. LTA zeolites showed significant incompressible behaviors at pressures between 2 and ∼7 GPa when it was compressed in helium. Based on careful analyses of the data together with the results of previous high-pressure studies, the incompressibility of LTA zeolites was induced by the penetration of a large amount of noble gas atoms into the cages of LTA zeolites under high pressures. The present results offer interesting and important information on the atomic diffusion process for open-structured materials under high pressures and thus have great implications for the development of new noble-gas-atom filled materials, as well as geochemical implications.

High-pressure and high-temperature experiments were carried out in a Mg2SiO4-H2 system using laser-heated diamond-anvil cells to understand the influence of H2 fluid on the stability of forsterite. In situ X-ray diffraction experiments and Raman spectroscopic measurements showed the decomposition of forsterite, and formation of periclase (MgO) and stishovite/quartz (SiO2) in the presence of H2 after being heated in the range between 2.5 GPa, 1400 K and 15.0 GPa, 1500 K. Transmission electron microscopic observation of the samples recovered from 15.0 GPa and 1500 K showed that the granular to columnar periclase grains maintained the original grain shape of forsterite, indicating that the periclase crystals crystallized under high temperature. On the other hand, euhedral columnar stishovite crystals were found at the boundaries between residual forsterite grains and reacted periclase. This implies that the SiO2 component was dissolved in H2 fluid, and that stishovite was considered to have crystallized when the solubility of the SiO2 component became reduced with decreasing temperature. Additional experiment on a SiO2-H2 system clearly showed the dissolution of quartz in H2 fluid, while those on a MgO-H2 system, periclase was hardly dissolved. These lines of evidence indicate that forsterite was incongruently dissolved in H2 fluid to form periclase crystals in the Mg2SiO4-H2 system, which is different from what was observed in the Mg2SiO4-H2O system. The results indicate that the stability of forsterite is strongly affected by the composition of coexisting C-O-H fluid.

The thermoelectric properties of the Kondo semiconductor CeRu4As12 with a filled skutterudite-type structure have been studied. The compound CeRu4As12 exhibits a hybridization gap insulating state with a small activation energy of 50 K. We report further results for CeRu4As12 synthesized at high temperatures and high pressures. Seebeck-coefficient and thermal-conductivity measurements have been performed on this material. The temperature dependence of the Seebeck coefficient for CeRu4As12 shows two peaks (around 90 K and 280 K). The phenomena could be related to the Kondo behavior at high temperatures and a hybridization gap-formation process at low temperatures.

We have measured the solubility of argon in SiO2 melt under high pressure by melting a SiO2 crystal at the argon pressure as high as 19 GPa using laser-heated diamond anvil cell (LHDAC). SiO2 was successfully melted at the pressure of about 12 GPa and recovered with a completely glassy phase. Above 15 GPa, the sample contained a large amount of crystalline SiO2, although it was completely melted and spherical due to the surface tension. This may arise from the change in the coordination number of Si in SiO2 melt at around 12–15 GPa, which is close to the triple point of coesite, stishovite, and liquid SiO2. Argon content in the recovered SiO2 was measured by energy-dispersive spectroscopy and mass spectrometry. It increased at pressures up to approximately 5–7 GPa and exhibited a constant value up to at least 12 GPa; this implies that, at these conditions, the noble gas behaves as an incompatible element. The result is completely different from those of previous LHDAC studies, which claimed that the increased solubility then dramatically drops above the pressure of about 5 GPa. Here, we report the new details of experimentally determined pressure dependence of noble gas solubility by LHDAC, and discuss the experimental difficulties and the structure change of silicate melt under high pressures.

Behavior of cubic spinel phase of Ag2MoO4 is investigated at high pressure using X-ray diffraction and Raman spectroscopy. The P–V data are fitted to a third order Birch–Murnaghan equation of state using a value of B0=113 GPa and B′0=4. The compound is also found to exhibit a phase transition around 5 GPa to a tetragonal structure and the two phases are found to coexist over a range of pressures. Raman spectra exhibit dramatic changes across the phase transition. Increase of X-ray background scattering and broadening of the Raman peaks associated with MoO4 tetrahedral ions in the high pressure phase suggest evolution of positional disorder. However, no evidence of pressure-induced amorphization was found up to 47 GPa.

We have investigated the high-pressure behavior of cristobalite in helium by powder X-ray diffraction. Cristobalite transformed to a new phase at about 8 GPa. This phase is supposed to have a molar volume of about 30 % larger than cristobalite, suggesting the dissolution of helium atoms in its interstitial voids. On further compression, the new phase transformed to a different phase which showed an X-ray diffraction pattern similar to cristobalite X-I at about 21 GPa. On the other hand, when the new phase was decompressed, it transformed to another new phase at about 7 GPa, which is also supposed to have a molar volume of about 25 % larger than cristobalite. On further decompression, the second new phase transformed to cristobalite II at about 2 GPa. In contrast to cristobalite, quartz did not show anomalous behavior in helium. The behavior of cristobalite in helium was also consistent with that in other mediums up to about 8 GPa, where the volume of cristobalite became close to that of quartz. These results suggest that dissolution of helium may be controlled not only by the density (amount of voids) but also by the network structure of SiO4 tetrahedra (topology of voids).

We designed new anvil assemblies for acquiring high-quality neutron diffraction data and ruby fluorescence spectra inside a sample chamber. The conical aperture of Ni-binded WC anvils was expanded by a factor of two. A hybrid gasket made of TiZr- and Al-alloy was developed to prevent outward extrusion. A small and optically transparent window of moissanite was introduced to allow for the determination of pressure and hydrostaticity by measurement of ruby fluorescence spectra. High pressure-generation tests that make use of Bi electrical conductivity and ruby pressure markers revealed that pressure could be determined over 10 GPa. In situ synchrotron X-ray diffraction experiments were also carried out using NaCl as the pressure calibrants. The maximum pressure achieved was approximately 13 GPa. The neutron diffraction intensity from the newly generated anvil assemblies was 2.5–3.0 times greater than that using the standard toroidal anvil assemblies used previously.

High-pressure and high-temperature phase relations of FeTiO3 were investigated up to a pressure of about 74 GPa and 2600 K by synchrotron X-ray diffraction and analytical transmission electron microscopy. We conclude that FeTiO3 ilmenite transforms into the following phase(s) with increasing pressure: FeTiO3 (perovskite) at 20–30 GPa, Fe2TiO4 (Ca2TiO4-type) + TiO2 (OI-type) at 30–44 GPa and high temperature, FeO (wustite) + TiO2 (OI) at 30–44 GPa and low temperature, and wustite + FeTi3O7 (orthorhombic phase) above 44 GPa. Among these dense high-pressure polymorphs, FeTi3O7 is a new compound and its structure analysis was tried using particle swarm optimization simulation. This method successfully found a new high-density FeTi3O7 structure, and Rietveld refinement based on this model structure gave an excellent fit with the experimentally obtained X-ray diffraction pattern. This new high-density FeTi3O7 structure consists of polyhedra for monocapped FeO7 prisms, bicapped TiO8 prisms, and tricapped TiO9 prisms, which develop on the b-c plane and stack along the a axis. The dense compound assemblage found in FeTiO3 is promising for investigating the behavior of ABX3 compounds under ultrahigh pressures.

X-ray diffraction measurements of distorted rutile-type oxyhydroxides β-GaOOH, InOOH, β-CrOOH, and β-CrOOD were taken at a maximum pressure of up to 35 GPa under quasi-hydrostatic conditions, at ambient temperature. Anomalies in the evolution of the relative lattice constants and the axial ratios of β-GaOOH, InOOH, and β-CrOOD suggest anisotropic stiffening along the a- and/or b-axes where the hydrogen bond is formed. The changes were observed at 15 GPa in β-GaOOH and InOOH and at 4 GPa in β-CrOOD. The pressures were higher in oxyhydroxides that have longer O…O distances of the hydrogen bond at ambient pressure. In contrast, such stiffening behavior was not observed in CrOOH, which has a significant short O…O distance and strong hydrogen bond. The stiffening behaviors observed in the present study can be attributed to the symmetrization of the hydrogen bonds in oxyhydroxides, as was previously found in δ-AlOOH(D).

The perovskite (Pv) to post-perovskite (PPv) phase transition and the deformation texture of the PPv phase were investigated on the basis of a high-pressure X-ray diffraction (XRD) study of CaIrO3 using a diamond-anvil cell in a pressure range up to 31 GPa. The development of a crystallographic preferred orientation (CPO) in the PPv phase was observed after the plastic deformation from 8 or 9 GPa to 31 GPa at both room and high (∼1500 K) temperatures. The observed CPOs in the present study indicate that the (0 1 0) plane worked as an active slip plane in the PPv phase over the entire pressure and temperature range of the present experiment. We also confirmed that the Pv to PPv phase transition proceeds at room temperature under high-stress conditions. The phase transition under high-stress condition is in stark contrast to the results of a previous hydrostatic experiment in which the Pv-CaIrO3 remained stable in a helium media at 31 GPa and room temperature. This indicates that shear stress plays an important role in the Pv to PPv phase transition, and this effect should be taken into account when the thermal structure at the D″ layer is discussed on the basis of the high-pressure experiments.

The nano-grained specimens of yttria-doped zirconia have been fabricated via a combination of low-temperature nano-powder synthesis and room-temperature high-pressure (4 GPa) compaction. The microstructure is essentially free from macroscopic pores but involves interfacial hydrated layers, which facilitate adsorption of water molecules within the specimens. The three kinds of proton-containing species, i.e., surface terminating OH groups, H-bonded H2O molecules and free H2O molecules, have been distinguished from each other by the Thermal Desorption Spectroscopy analysis in terms of thermal stability, and also by the 1H MAS-NMR measurements. The electric conduction in humidified atmospheres is dominated essentially by proton hopping below ca. 800 K, which is verified by the H/D isotope effect and water vapor pressure dependence. The effect of grain growth on the conductivity suggests that the protonic conduction path is the grain boundary or interface. The present study shows a good feasibility of fabricating proton-conducting materials based on nano-grained oxides, even if the bulk property involves negligible proton solubility and conductivity, by the formation of grain boundary network of interfacial hydration layer.

A new opposed-anvil high pressure and temperature apparatus was developed based on the Drickamer-type apparatus. Various improvements were made to increase the sample volume and to generate high pressure and temperature stably and easily. By optimizing components such as the anvil, heater, and gasket, large sample volumes of about 4 mm3 (∼103 times more than that previously obtained with our previous apparatus) were achieved, with compact and light apparatus (outer diameter ϕ 40 mm; height 31 mm; weight 300 g). Pressures and temperatures up to about 15 GPa and 1700 K can routinely and stably be achieved by using this assembly. In order to extend the pressure range further, sintered diamond was used as an anvil material. As a result, pressures and temperatures of around 38 GPa and 1400 K were achieved, although the sample volume was decreased to about 1.3×10−1 mm3.

High pressure and temperature reactions of a mixture of forsterite and hydrogen molecules have been carried out using a laser heated diamond anvil cell at 9.8–13.2 GPa and ~1,000 K. In situ X-ray diffraction measurements showed no sign of decomposition or phase transitions of the forsterite under these experimental conditions, indicating that the olivine structure was maintained throughout all runs. However, a substantial expansion of the unit cell volume of the forsterite was observed for samples down to ~3 GPa upon quenching to ambient pressure at room temperature. The Raman spectroscopy measurements under pressure showed significant shifts of the Raman peaks of the Si–O vibration modes for forsterite and of the intramolecular vibration mode for H2 molecules toward a lower frequency after heating. Additionally, no OH vibration modes were observed by Raman and FT-IR spectroscopic measurements. These lines of evidence show that the observed volume expansion in forsterite is not explained by the incorporation of hydrogen atoms as hydroxyl, but suggest the presence of hydrogen as molecules in the forsterite structure under these high pressure and temperature conditions.

A neutron powder diffraction experiment was conducted to refine the hydrogen position of Mg-endmember deuterated wadsleyite. Preliminary refinement using the dry-structure determined by single crystal X-ray diffraction reveals a maximum peak Q1 of nuclear density in the difference Fourier map at the M3 octahedral edge, between the O1 and O4 atoms (3.071(3) A). Full Rietveld refinement was conducted assuming that the maximum peak corresponds to deuterium atom. The deuterium position was determined as (0.096, 0.289, 0.315) with occupancy of 8.2%. The O1–D1 vector lies along M3 octahedral edge pointing O4 atom, and the bond length is determined as 1.037(15) A for O1–D1, and 2.041(15) A for D1⋯O4. The O1–D1⋯O4 geometry is almost linear with angle of 171.7(5) °. The residual peak Q2 was found in the map at (0, 0.172, 0.268), suggesting the existence of a bent hydrogen bond between O1⋯O3 (3.035 A) of the M3 octahedral edge. The respective distances from the surrounding oxygen atoms are 0.97 and 2.13 A for O1–Q2 and Q2⋯O3. The O1–Q2⋯O3 configuration is nonlinear, with angle of 154.4 °. These results reveal that the dominant site of protonation in wadsleyite is the O1 site, which is consistent with the previous prediction.

The rock salt (B1) structure of binary oxides or chalcogenides transforms to the CsCl (B2) structure under high pressure, with critical pressures P(s) depending on the cation to anion size ratio (R(c)/R(a)). We investigated structural changes of A(2)MO(3) (A = Sr, Ca; M = Cu, Pd) comprising alternate 7-fold B1 AO blocks and corner-shared MO(2) square-planar chains under pressure. All of the examined compounds exhibit a structural transition at P(s) = 29-41 GPa involving a change in the A-site geometry to an 8-fold B2 coordination. This observation demonstrates, together with the high pressure study on the structurally related Sr(3)Fe(2)O(5), that the B1-to-B2 transition generally occurs in these intergrowth structures. An empirical relation of P(s) and the R(c)/R(a) ratio for the binary system holds well for the intergrowth structure also, which means that P(s) is predominantly determined by the rock salt blocks. However, a large deviation from the relation is found in LaSrNiO(3.4), where oxygen atoms partially occupy the apical site of the MO(4) square plane. We predict furthermore the occurrence of the same structural transition for Ruddlesden-Popper-type layered perovskite oxides (AO)(AMO(3))(n), under higher pressures. For investigating the effect on the physical properties, an electrical resistivity of Sr(2)CuO(3) is studied.

The pressure responses of portlandite and the isotope effect on the phase transition were investigated at room temperature from single-crystal Raman and IR spectra and from powder X-ray diffraction using diamond anvil cells under quasi-hydrostatic conditions in a helium pressure-transmitting medium. Phase transformation and subsequent peak broadening (partial amorphization) observed from the Raman and IR spectra of Ca(OH)2 occurred at lower pressures than those of Ca(OD)2. In contrast, no isotope effect was found on the volume and axial compressions observed from powder X-ray diffraction patterns. X-ray diffraction lines attributable to the high-pressure phase remained up to 28.5 GPa, suggesting no total amorphization in a helium pressure medium within the examined pressure region. These results suggest that the H–D isotope effect is engendered in the local environment surrounding H(D) atoms. Moreover, the ratio of sample-to-methanol–ethanol pressure medium (i.e., packing density) in the sample chamber had a significant effect on the increase in the half widths of the diffraction lines, even at pressures below the hydrostatic limit of the pressure medium.

δ-Al(OD) 3 powders were synthesized from Al(OD) 3 bayerite at 4 GPa and 523 K using a cubic press apparatus. Neutron powder diffraction analyses of δ-Al(OD) 3 at ambient conditions revealed that the crystals are orthorhombic with space group P 2 1 2 1 2 1 , not Pnma as reported previously based on X-ray diffraction data. The P 2 1 2 1 2 1 δ-Al(OH) 3 structure contains seven independent atoms in the asymmetric unit, including one Al, three O, and three H atoms. The initial lattice parameters and the atomic positions of both Al and O were taken from previous X-ray structural analyses of the Pnma structure, while the positions of H were determined in the present study using ab initio calculations to (1) give the least energy among trial structural models for P 2 1 2 1 2 1 δ-Al(OH) 3 , (2) accurately reproduce the measured lattice parameters of δ-Al(OD) 3 , and (3) show reasonable energetic relations between the Al(OH) 3 polymorphs; namely, gibbsite is stable at ambient pressure, δ-Al(OH) 3 has the lowest enthalpy at pressure greater than 1.1 GPa, and both bayerite and η-Al(OH) 3 are metastable over the entire pressure range. Furthermore, we found that the structure of δ-Al(OH) 3 obtained from ab initio calculations is in good agreement with that derived from a Rietveld refinement of δ-Al(OD) 3 , based on the present powder neutron diffraction data. The δ-Al(OH) 3 structure possesses one relatively long and two short O-H···O hydrogen bonds. Ab initio calculations also reveal that δ-Al(OH) 3 with space group P 2 1 2 1 2 1 transforms to another high-pressure polymorph with space group Pnma at around 67 GPa, and that the two short hydrogen bonds in δ-Al(OH) 3 become both symmetric through the P 2 1 2 1 2 1 to Pnma transformation, in which the protons are located at the midpoints of the O···O hydrogen bonds.