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The high-pressure phase of ammonia borane (NH3BH3) observed at ∼1.2 GPa has been reported to result in pressure-induced formation of dihydrogen bonds at ∼4 GPa. In this study, we performed high-pressure x-ray diffraction measurements on the high-pressure phase (up to ∼10.2 GPa) using a He hydrostatic pressure medium to examine the influence of the formation of dihydrogen bonds on the lattice parameters and unit cell volume of NH3BH3. We observed a unique behavior in the pressure dependence of lattice parameters close to the pressure at which the dihydrogen bond was formed. The lattice parameters demonstrated hysteresis curves under compression and decompression conditions but the unit cell volume did not. Moreover, the pressure dependence of the unit cell volume could not be expressed using a single Birch–Murnaghan equation within an acceptable margin of error, thus suggesting a change in bulk modulus under compression. These results are considered to have originated from the pressure-induced formation of dihydrogen bonds. Moreover, high-pressure Raman scattering measurements and a simulation using density functional theory calculations revealed the vibrational modes of the high-pressure phase of NH3BH3. The results demonstrated that librational modes were enhanced by forming dihydrogen bonds. Moreover, the intramolecular stretching modes of BN, BH, and NH monotonically shifted with pressure, while the symmetrical in-plane bending modes of BH3 and NH3 split irrespective of the formation of dihydrogen bonds.

High-pressure X-ray and neutron diffraction analyses of an ambient-pressure phase (AP) and two high-pressure phases (HP1 and HP2) of ammonia borane (i.e., NH3BH3 and ND3BD3) were conducted to investigate the relationship between their crystal structures and dihydrogen bonds. It was confirmed that the hydrogen atoms in AP formed dihydrogen bonds between adjacent molecules, and the H-H distance between the hydrogen atoms forming this interaction was shorter than 2.4 A, which was nearly 2 times larger than the van der Waals radius of hydrogen. In the case of half of the hydrogen bonds, a phase transition from AP to the first high-pressure phase (HP1) at ∼1.2 GPa resulted in an increase in the H-H distances, which suggested that the dihydrogen bonds were broken. However, when HP1 was further pressurized to ∼4 GPa, all of the H-H distances became shorter than 2.4 A again, which implied the occurrence of pressure-induced re-formation of the dihydrogen bonds. It was speculated that the re-formation was consistent with a second-order phase transition suggested in previous studies by Raman spectroscopy and X-ray diffraction measurement. Furthermore, at ∼11 GPa, HP1 transformed to the second high-pressure phase (HP2), and its structure was determined to be P21 (Z = 2). In this phase transition, the inclination of the molecule axis became larger, and the number of types of dihydrogen bonds increased from 6 to 11. At 18.9 GPa, which was close to the upper pressure limit of HP2, the shortest dihydrogen bond decreased to ∼1.65 A. Additionally, the X-ray diffraction results suggested another phase transition to the third high-pressure phase (HP3) at ∼20 GPa. The outcomes of this study confirmed experimentally for the first time that the structural change under pressure causes the breakage and re-formation of the dihydrogen bonds of NH3BH3.

Pressure-volume-temperature (P-V-T) data of synthetic Mg7Si2O8(OH)6 phase A were collected under P-T conditions up to ~10.5 GPa and 900 K by energy-dispersive X-ray diffraction using a cubic type multi-anvil apparatus, MAX80, located at the Photon Factory–Advanced Ring (PF-AR) at the High Energy Accelerator Research Organization (KEK). P-V EoS using only room-temperature data yielded V0 = 511.6(2) Å3, KT0 = 106.8(18) GPa, and pressure derivative KT′ = 3.88(38). These parameters were consistent with the subsequent equation of state (EoS) analysis. The compressibility of phase A was anisotropic, with its a-axis being ~26% more compressible than the c-axis, which is normal to the plane of the distorted close-packed layers. A fit of the present data to the high-temperature Birch-Murnaghan EoS yielded V0 = 511.7(3) Å3, K0 = 104.4(24) GPa, K′ = 4.39(48), (∂KT/∂T)P = –0.027(5) GPa K–1, and thermal expansion α = a + bT with values of a = 2.88(27) × 10–5 K–1 and b = 3.54(68) × 10–8 K–2. The lattice dynamical approach by the Mie-Grüneisen-Debye EoS yielded θ0 = 928(114) K, q = 2.9(10), and γ0 = 1.19(8). The isobaric heat capacity CP of phase A at 1 atm. was calculated based on the Mie-Grüneisen-Debye EoS fit of present P-V-T data. In addition, the density profiles of subducting slabs with different degrees of serpentinization were also calculated along the cold geotherm up to ~13 GPa. The serpentinization of subducting slab will significantly lower the density of slab at shallower depth; however, this effect becomes negligible when antigorite dehydrates to phase A. Because the phase A bearing subducting slab is supposed to be denser than the surrounding mantle, the water can transport into deeper parts of the upper mantle and the transition zone.

A technique for density measurement under high pressure and high temperature was developed using the X-ray absorption imaging method combined with an externally heated diamond anvil cell. The densities of solid and liquid In were measured in the pressure and temperature ranges of 3.2–18.6 GPa and 294–719 K. The densities obtained through the X-ray absorption imaging method were in good agreement (less than 2.0% difference) with those obtained through X-ray diffraction. Based on the measured density, the isothermal bulk modulus of solid In is determined as 48.0 ± 1.1−40.9 ± 0.8 GPa at 500 K, assuming K ′ = 4 to 6. The compression curve of liquid In approaches that of solid In at higher pressures and does not cross over the solid compression curve in the measurement range. The present technique enables us to determine the densities of both solids and liquids precisely in a wide pressure and temperature range.

The isomer shift of the 57Fe nuclei is an important 57Fe hyperfine interaction parameter to discuss the electronic states of the Fe atoms. To evaluate the isomer shift of the 57Fe nuclei in materials, we have measured 57Fe nuclear forward scattering spectra of a sample with and without an α-Fe foil in which its magnetic hyperfine field was aligned by external magnetic field. Since the 57Fe nuclear transitions in the α-Fe foil are selected in these experimental conditions, we precisely evaluate the absolute center shift of the 57Fe nuclei in the sample. The performance of this method was demonstrated using paramagnet stainless steel, sodium nitroprusside and antiferromagnet EuFe2As2 at ambient pressure and 1.4 GPa.

A new Al-bearing high-pressure hydrous Mg-silicate named 23 A phase with a hexagonal structure, which is stable in chlorite composition and could be an important water carrier in the subducting slab, was reported by Cai et al. (2015a). Here, for the first time, we determined the equation of state of the 23 A phase up to 10 GPa and 1073 K by energy-dispersive in situ X-ray diffraction. Fitting the P-V data to the room temperature Birch-Murnaghan equation of state yielded V0 = 538.0(3) A3 and K0 = 111(1) GPa by fixing K′ at 4. The high temperature 3rd order Birch-Murnaghan equation of state was used to fit the P-V-T data, yielding V0 = 538.0(3) A3, K0 = 109(1) GPa, ∂K/∂T = −0.012(5) GPa/K, and a0 = 3.0(4) × 10−5/K by fixing K′ at 4. Very little anisotropy was observed, and the axial compressibilities were 2.54(2) 10−3/GPa for the a axis and 2.68(5) 10−3/GPa for the c axis. The 23 A phase has similar volume compressibility and density as phase A, indicating that the stability region (or the depth in the subduction zone) of these phases are close to each other. This is consistent with the observations of Cai et al. (2015a). Based on the present results, the potential effect of hydration on the physical properties of the subduction slab were discussed, and the possible formation enthalpy and entropy of the 23 A phase were calculated.

The effects of pressure and temperature on the lattice constants and thermal expansion coefficients of Indium were studied up to 18.6 GPa and 506 K by using in situ X-ray diffraction method with an externally heated diamond anvil cell. Indium exhibits a tetragonal structure. The measured c/a ratio of tetragonal structure decreases with increasing temperature and its temperature dependence decreases with increasing pressure. The thermal expansion coefficient of the a-axis also decreases with increasing pressure up to 7 GPa and remains almost constant above 7 GPa, whereas that of the c-axis increases monotonously with pressure and changes from negative to positive at around 7 GPa. The observed behavior suggests that temperature reduces the tetragonal distortion of indium, and its effect is dominant below 7 GPa; in contrast, pressure enhances lattice distortion, and tends to have a stronger effect above 7 GPa.

The phase relationships of the Fe-Ni-S system at 15 GPa were studied by high pressure quench experiments. The stability fields of (Fe,Ni)3S and (Fe,Ni)3S2 and the melting relationships of the Fe-Ni-S system were determined as a function of Ni content. The (Fe,Ni)3S solid solution is stable in the composition of Ni/(Fe + Ni) > 0.7 and melts incongruently into an Fe-Ni alloy + liquid. The (Fe,Ni)3S2 makes a complete solid solution and melts incongruently into (Fe,Ni)S + liquid, whose structure was determined to show Cmcm-orthorhombic symmetry by in situ synchrotron X-ray diffraction experiments. The eutectic contains about 30 at.% of S, and its temperature decreases with increasing Ni content with a rate of ∼5 K/at.% from 1175 K. The density of the Fe-FeS eutectic composition (Fe70S30) liquid is evaluated to be 6.93 ± 0.08 g/cm3 at 15 GPa and 1200 K based on the Clausius-Clapeyron relations and densities of subsolidus phases. The Fe-Ni-S liquids are a primary sulfur-bearing phase in the deep mantle with a reducing condition (250–660 km depth), and they would play a significant role in the carbon cycle as a carbon host as well as in the generation of diamond.

The high-pressure behavior of gallium arsenide, GaAs, has been investigated using an in-situ X-ray powder diffraction technique in a diamond anvil cell combined with a resistance heating method, at pressures and temperatures up to 25 GPa and 1000 K respectively. The pressure-induced phase transition from a zincblende to an orthorhombic ( Cmcm ) structure was observed. This transition occurred at 17.3 GPa and at room temperature, where a negative temperature dependence for this transition was confirmed. The transition boundary was determined to be P (GPa) = 18.0 − 0.0025 × T (K).

The high-pressure behaviour of zinc sulphide, ZnS, has been investigated, using an in situ X-ray powder diffraction technique in a diamond anvil cell, at pressures and temperatures up to 35 GPa and 1000 K, respectively. The pressure-induced phase transition from a zincblende (B3) to a rocksalt (B1) structure was observed. This transition occurred at 13.4 GPa and at room temperature, and a negative dependence on temperature for this transition was confirmed. The transition boundary was determined to be P (GPa) = 14.4 − 0.0033 × T (K).

The phase boundary between coesite and stishovite in SiO2 was determined over the range of 1200–1700 K using a multi-anvil high-pressure apparatus combined with the synchrotron X-ray diffraction technique. The stability of each phase was determined by observing the powdered X-ray diffraction data. The transition boundary between the coesite and stishovite phases was found to occur at P (GPa) = 4.7 + 0.0031 × T (K). The transition pressure determined in this study was in general agreement with what was observed in previous high-pressure experiments and heat capacity measurements. However, the slope of the transition, dP/dT, determined in our study was higher than that estimated in a previous study utilized with the in situ X-ray method. In contrast, the slope calculated by the heat capacity data was in good agreement with that determined in our study. The phase transition determined in our study occurs at around 10 GPa at the normal mantle geotherm, coinciding with the seismic discontinuity around 300 km depth known as the X-discontinuity.

The phase boundary between akimotoite and ringwoodite + stishovite in MgSiO3 was determined using a multi-anvil high-pressure apparatus and synchrotron X-ray radiation. The phase relation was determined by observing the recovered samples using an electron microprobe analyzer. Experimental pressures were monitored by the in situ powdered X-ray diffraction data of gold, which was put in the sample chamber. The reaction boundary between akimotoite and ringwoodite + stishovite was found to occur at P (GPa) = 22.0–0.0012 × T (K). The pressure dependence of the slope of the reaction boundary, dP/dT, determined in our study was smaller than that determined by Gasparik (J Geophys Res 95:15751–15769, 1990). The triple point of ringwoodite + stishovite–wadsleyite + stishovite–akimotoite estimated in our study was at ~20 GPa and ~1700 K.

The high pressure behavior of gallium phosphide, GaP, has been examined using the synchrotron X-ray diffraction technique in a diamond anvil cell up to 27 GPa and 900 K. The transition from a semiconducting to a metallic phase was observed. This transition occurred at 22.2 GPa and room temperature, and a negative dependence of temperature of this transition was found. The transition boundary was determined to be P (GPa) = 22.6 − 0.0014 × T (K).

Amorphous carbon films have several outstanding tribology characteristics, including high hardness, surface smoothness, and low friction. Under tribological conditions, their surface is generally exposed to high-temperature and pressure. Although the structure of amorphous carbon films is likely changed by high temperature and pressure, there have been no reports on such structural changes of the films. To obtain information about their structural changes, synchrotron X-ray diffraction was used to analyze two kinds of amorphous carbon films, a-C:H and a-C:H:Si, under high-temperature and high-hydrostatic pressure conditions. Synchrotron X-ray diffraction was applied to films pressurized by a multi-anvil press installed in the PF-AR NE5C beamline at KEK at room temperature and at a high-temperature around 200 °C. The pair distribution functions derived by Fourier transformation of the obtained scattering intensity profiles showed that the sp2/sp3 ratios for both films decreased as the pressure increased and that the sp2/sp3 ratio for the a-C:H film increased as the temperature increased. This indicates that high-pressure creates sp3 stabilization in a-C:H and a-C:H:Si films while high-temperature creates sp2 transition in a-C:H film. The sp2/sp3 ratio for the a-C:H:Si film did not change much even at high-temperature due to the high thermal-oxidative stability of a-C:H:Si.

Recent advances in techniques for high-pressure and high-temperature experiments enable us to measure the velocity of sound in liquid Fe alloys. However, reported velocities in liquid Fe–S differ among research groups (e.g., by >10% at 5 GPa), even when similar methods are used (i.e., the ultrasonic pulse–echo overlap method combined with a large volume press). To identify the causes of the discrepancies, we reanalyzed previous data and conducted additional sound velocity measurements for liquid Fe–S at 2–7 GPa, and evaluated the potential error sources. We found that the discrepancy cannot be explained by errors in the sound velocity measurements themselves, but by inaccuracies in determining the temperature, pressure, and chemical composition in each experiment. Of particular note are the significant errors introduced when determining pressures from the unit-cell volume of MgO, which is a temperature-sensitive pressure standard, using inaccurate temperatures. To solve the problem, we additionally used h-BN as a pressure standard, which is less sensitive to temperature. The pressure dependence of the sound velocity became smaller than that of the original data because of the revised pressure values. Our best estimate for the seismic velocity of the Moon’s liquid outer core is 4.0 ± 0.1 km/s, given a chemical composition Fe 83 S 17 .

The interplay between magnetism and superconductivity is one of the important subjects to investigate the pairing mechanism in novel superconductors. We have found a new coexistence between an antiferromagnetic order in the Fe sublattice and superconductivity of the FeAs-based ${\mathrm{EuFe}}_{2}{\mathrm{As}}_{2}$ superconductor in the pressure range from 2.4 to 3.0 GPa by $^{57}\mathrm{Fe}$ nuclear forward scattering (NFS) using a single-crystal sample. The magnetic state in the Fe sublattice changes to a new antiferromagnetic one with superconductivity from a stripe-type antiferromagnetic one observed in the normal conducting state at 2.7 GPa. Below the superconducting transition temperature, the temperature dependence of $^{57}\mathrm{Fe}$ NFS spectra reveals that the new antiferromagnetic order develops with the superconductivity. This nontrivial coupling of two ordered states in ${\mathrm{EuFe}}_{2}{\mathrm{As}}_{2}$ under pressure demonstrates a new and intriguing relationship between magnetism and superconductivity in Fe-based superconductors.

A novel LiNbO3-type (LN-type) lead zinc oxide, PbZnO3, was successfully synthesized under high pressure and temperature. Rietveld structure refinement using synchrotron powder X-ray diffraction (XRD) data demonstrated that LN-type PbZnO3 crystallized into a trigonal structure with a polar space group (R3c). The bond valence sum estimated from the interatomic distances indicated that the sample possesses a Pb(4+)Zn(2+)O3 valence state. Polarization could evolve as a result of the repulsion between constituent cations because PbZnO3 does not contain a stereochemical 6s(2) cation or a Jahn-Teller active d(0) cation. Distortion of ZnO6 octahedra resulting from cation shift is comparable with that of d(0) TiO6 in ZnTiO3 and MnTiO3 with LN-type oxides, which leads to stabilization of the polar structure. PbZnO3 exhibited metallic behavior and temperature-independent diamagnetic character. In situ XRD measurement revealed that the formation of LN-type PbZnO3 occurred directly without the formation of a perovskite phase, which is unusual among LN-type materials obtained by high-pressure synthesis.

Simple-shear deformation experiments on polycrystalline olivine and olivine single-crystal were conducted at pressures of 1.3–3.8 GPa and temperatures of 1223–1573 K to understand the achievement of steady-state fabric strength and the process of dynamic recrystallization. Development of crystallographic preferred orientation (CPO) of olivine was evaluated from two-dimensional X-ray diffraction patterns, and shear strain was measured from X-ray radiographs. The steady-state fabric strength of the A-type fabric was achieved within total shear strain of γ = 2. At strains higher than γ = 1, an increase in concentration of the [0 1 0] axes mainly contributes to an increase in fabric strength. At strains higher than γ = 2, the magnitude of V SH / V SV (i.e., ratio of horizontally and vertically polarized shear wave velocities) scarcely increased in most of the runs. The V SH / V SV of peridotite (70 vol.% olivine + 30 vol.% minor phases) having the steady-state A-type olivine fabric coincides with that of recent global one-dimensional models under the assumption of horizontal flow, suggesting that the seismic anisotropy observed in the shallow upper mantle is mostly explained by the development of A-type olivine fabric. Experimental results on the deformation of single-crystal olivine showed that the CPO of olivine is influenced by the initial orientation of the starting single crystal because strain is concentrated in the recrystallized areas and the relic of the starting single crystal remains. In the upper mantle, the old CPO of olivine developed in the past may affect the olivine CPO developed in the present.

The high-pressure behavior of zirconium has been examined using the synchrotron X-ray diffraction technique to a pressure of 38 GPa and a temperature of 800 K employing a hydrothermal diamond anvil cell technique. The structural transition from the ω to the β phase was observed. This transition has a negative d P /d T gradient, which is in general agreement with those reported in previous studies. The transition boundary was determined to be, P (GPa)=41.2–0.025× T (K). The negative slope of the transition, d P /d T , determined in our study using the diamond anvil cell technique was less than half that estimated by the previous study using a large press apparatus.

Some high-pressure structures of lithium borohydride (LiBH4) were analyzed using the Rietveld refinement for high-pressure X-ray diffraction data up to 50 GPa, and also by the density functional theory (DFT) calculation, the molecular dynamics (MD) simulation and Raman scattering spectrum. The structure of the first high-pressure phase at room temperature (phase III) was proposed to be an I41/acd structure, whose unit cell is composed of a √2 × √2 × 2 supercell of the previously reported Ama2 structure. However, the BH4– ions in our model were found to have different orientations from that of the Ama2 model. The structure of the second high-pressure phase (phase V′) that appeared at 17 GPa was proposed to be the tetragonal I4/mmm structure, where the hydrogen atoms were disordered in the same way as that of an ambient phase of NaBH4 (Fm3m structure). When the pressure was elevated to 30 GPa, the tetragonal I4/mmm structure gradually deformed to a cubic Fm3m structure, which had previously been reported ...

The last remaining marcasite-type RuN2 was successfully synthesized by direct chemical reaction between ruthenium and molecular nitrogen above the pressure of 32 GPa. For the first time, we found that Ru 4d is weakly hybridized with N 2p in the structure by using transmission electron microscopy equipped with electron-energy-loss spectroscopy. Our finding give important knowledge about the platinum-group pernitride with respect to the chemical bonding between platinum-group element and nitrogen.

The equation of state of natural antigorite has been determined up to ∼10 GPa and 500 °C by in situ X-ray diffraction in a cubic type multi-anvil apparatus, MAX80, located at the Photon Factory-Advanced Ring at the High Energy Accelerator Research Organization (KEK), and the temperature dependence of the bulk modulus was determined for the first time by high pressure and high temperature X-ray diffraction based on a series of direct measurements. No dehydration occurred during the entire experimental process, and no significant deviatoric stress was observed after heating. The room temperature P–V data below 7 GPa have been fit to the Birch-Murnaghan equation of state, yielding V 0,300 K = 366.9(7) A 3 , K 0, 300 K = 65.2(31) GPa, and the pressure derivative K ′ fixed to 6.1. The high pressure phase transition was observed through volume softening behavior at around 7 GPa, and the dP/dT slope seems to be flat or slightly positive, which is consistent with the recent report by Bezacier et al. (2013) . The high temperature Birch-Murnaghan equation of state was used to fit the P–V–T data below 7 GPa. Since the present experimental data was obtained by energy dispersive X-ray diffraction at high pressure and high temperature, the resolution was slightly lower than that obtained by the angle dispersive X-ray method. So the bulk modulus K 0, 300 K and the pressure derivative K ′ were fixed to 62.9 GPa and 6.1, respectively, which was obtained by single crystal X-ray diffraction in a diamond anvil cell by means of the angle dispersive method ( Nestola et al., 2010 ) during fitting. From the fitting, we obtained V 0, 300 K = 367.3(2) A 3 , dK/dT = −0.0265(41) GPa/K, thermal expansion α 0 = 3.92(50) × 10 −5 /K. The temperature dependence of the bulk modulus was larger than the value calculated empirically ( Holland and Powell, 1998 ). The thermal expansion of antigorite is larger than the results from the previous study. The compression of antigorite is very anisotropic along three axes, with a ratio of 1.15:1.00:3.33 at room temperature. Considering the P–T conditions of the subducting slab, the phase transition of antigorite may occur only in a limited area in the slab.

In order to investigate effects of the post-spinel transformation on rheological behavior of descending slabs, we conducted simultaneous deformation and eutectoid reaction experiments using an analogue reaction from albite to jadeite and quartz by a deformation-DIA apparatus. Flow stress and transformed fraction were quantitatively obtained by in-situ X-ray observations during the constant strain rate deformation. The microstructures of recovered samples as well as the flow and kinetic data suggest sequential variation of the creep mechanism from dislocation creep of the transformed eutectoid colony followed by the grain-size sensitive creep in the degenerated eutectoid structure. Our study demonstrated that the creep behavior during the eutectoid transformation involves various processes than previously thought. The slabs may not be weaken promptly after entering into the lower mantle when the size of eutectoid colony is enough large, and keep their strength (or harden) over a period of time depending on the degeneration kinetics of the colony.

The equation of state (EOS) of titanium boride, TiB2, was investigated by in situ X-ray diffraction in a diamond anvil cell and multianvil high-pressure apparatus. The pressure-volume-temperature (P-V-T) data were collected at up to 111 GPa and room temperature for the diamond-anvil cell experiments and at up to 15 GPa and 1300 K for the multianvil experiments. No phase transition was observed through the entire range of experimental conditions. The pressure-volume data at room temperature were fitted using a Vinet EOS to obtain the isothermal bulk modulus, BT0 = 256.7 GPa, and its pressure derivative, B' T0 = 3.83. When fitting a thermal EOS using the P-V-T data for the multianvil experiments, we find that [Formula: see text] = 0.095 (GPa/K) and α 0 = 2.49 × 10-5 K-1.

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.

We used an in situ measurement method to investigate the phase transition of Fe2SiO4 polymorphs under high pressures and temperatures. A multi-anvil high-pressure apparatus combined with synchrotron X-ray radiation was used. The stability of each polymorph was identified by observing the X-ray diffraction data from the sample. In most experiments, the diffraction patterns were collected 10–30 min after reaching the desired pressure and temperature conditions. The transition boundary between the olivine and spinel phase at T = 1,000–1,500 K and P = 2–8 GPa was determined to occur at P (GPa) = 0.5 + 0.0034 × T (K). The transition pressure determined in this study was in general agreement with that observed in previous high-pressure experiments. However, the slope of the transition, dP/dT, determined in our study was significantly higher than that estimated by the previous study combined with the in situ X-ray method.

A novel LiNbO3-type (LN-type) lead zinc oxide, PbZnO3, was successfully synthesized under high pressure and temperature. Rietveld structure refinement using synchrotron powder X-ray diffraction (XRD) data demonstrated that LN-type PbZnO3 crystallized into a trigonal structure with a polar space group (R3c). The bond valence sum estimated from the interatomic distances indicated that the sample possesses a Pb(4+)Zn(2+)O3 valence state. Polarization could evolve as a result of the repulsion between constituent cations because PbZnO3 does not contain a stereochemical 6s(2) cation or a Jahn-Teller active d(0) cation. Distortion of ZnO6 octahedra resulting from cation shift is comparable with that of d(0) TiO6 in ZnTiO3 and MnTiO3 with LN-type oxides, which leads to stabilization of the polar structure. PbZnO3 exhibited metallic behavior and temperature-independent diamagnetic character. In situ XRD measurement revealed that the formation of LN-type PbZnO3 occurred directly without the formation of a perovskite phase, which is unusual among LN-type materials obtained by high-pressure synthesis.

Deformation experiments on hydrous melt-bearing dunite (olivine+4 vol% orthopyroxene+4 vol% clinopyroxene with less than 2.5 vol% of the melt phase) were conducted at pressures of 1.3–5.7 GPa and temperatures of 1270–1490 K in order to explore the effect of intergranular fluids on the plastic flow of olivine in Earth’s upper mantle. The strain rate was proportional to steady-state creep strength to the 2.1 power, and the creep strength markedly increased with increase in grain size. Developments of the crystallographic preferred orientation of olivine and flattening of olivine grains were hardly observed even after 33–55% shortening of the samples. These observations show that grain boundary sliding (GBS) dominated the deformation of olivine (i.e., superplasticity). The creep strength of hydrous melt-bearing dunite was 2–5 times lower than that of melt-free dunite. The dependence of creep rate on melt fraction is known to be expressed empirically as e ( ϕ ) = e ( 0 ) exp ( α ϕ ) , where α is a constant and ϕ is the melt fraction. The experimentally obtained value of α was in the range of 150–230, corresponding to 5–7 times the reported values for the olivine–basalt system at 0.3 GPa (i.e., creep strength of dunite was efficiently reduced by the hydrous melt). Superplasticity is the dominant creep mechanism of olivine in fluid-bearing fine-grained peridotites under low-temperature and high-stress conditions (i.e., peridotite shear zones in the upper mantle). Superplasticity induced by geological fluids would play an important role in the shear localization (and thus initiation of subduction) in the upper mantle.

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).

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.

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.

A system for deformation experiments under high pressure using a deformation cubic apparatus, with monochromatic synchrotron radiation, has been developed at beamline AR-NE7A, Photon Factory, KEK High Energy Accelerator Research Organization, Japan. We have conducted deformation experiments of fayalite using this new system at pressures up to 5 GPa and temperatures up to 1073 K, and successfully conducted the stress and strain measurements during the deformation.

The compositional dependence on the density of liquid Fe alloys under high pressure is important for estimating the amount of light elements in the Earth’s outer core. Here, we report on the density of liquid Fe–Si at 4 GPa and 1,923 K measured using the sink–float method and our investigation on the effect of the Si content on the density of the liquid. Our experiments show that the density of liquid Fe–Si decreases from 7.43 to 2.71 g/cm3 non-linearly with increasing Si content (0–100 at%). The molar volume of liquid Fe–Si calculated from the measured density gradually decreases in the compositional range 0–50 at% Si, and increases in the range 50–100 at% Si. It should be noted that the estimated molar volume of the alloys shows a negative volume of mixing between Fe and Si. This behaviour is similar to Fe–S liquid (Nishida et al. in Phys Chem Miner 35:417–423, 2008). However, the excess molar volume of mixing for the liquid Fe–Si is smaller than that of liquid Fe–S. The light element contents in the outer core estimated previously may be an underestimation if we take into account the possible negative value of the excess mixing volume of iron–light element alloys in the outer core.

We investigated the pressure-induced structural changes in hydrous forsterite and enstatite melts using in situ synchrotron X-ray diffraction. Diffraction data was collected up to 6.9 GPa at superliquidus temperatures. At pressures below 3 GPa, the first sharp diffraction peak (FSDP), which reflects the silicate network ordering in the silicate melts that consist of … Si O Si … linkages, is shifted notably toward higher Q (scattering vector [A− 1]) in both melt compositions. This observation indicates that water has a depolymerizing effect on the silicate network below 3 GPa, which means that … Si O Si … linkages are partially disrupted by hydroxyl species (Si-OH units). In contrast, the peaks move to lower Q at pressures above 3 GPa in spite of the compression, which indicates lengthening of the silicate network ordering (i.e., polymerization of silicate network). This observation indicates that water changes to have a polymerizing effect on the silicate network above 3 GPa by a new free hydroxyl group such as Mg-OH, which was previously proposed in the study on hydrous silicate glasses structure. In fact, the structural changes in the present study are more pronounced in the hydrous Mg2SiO4 melt, suggesting that the MgO component has an important influence on the polymerization of hydrous melt structure at 3–5 GPa. The present structural change, re-polymerization at high pressure, in hydrous silicate melt can influence the viscosity. Such a relatively high-viscosity hydrous magma may be able to stay (or be decreased in the rising velocity) at a depth of 100–180 km, which can enhance the decrease in a seismological wave velocity in the Earth's asthenosphere as proposed in previous seismological observations.

We used an in situ measurement method to investigate the phase transition of CaGeO3 polymorphs under high pressures and temperatures. A multi-anvil high-pressure apparatus combined with intense synchrotron X-ray radiation was used. The transition boundary between a garnet and a perovskite phase at T = 900–1,650 K and P = 3–8 GPa was determined as occurring at P (GPa) = 9.0−0.0023 × T (K). The transition pressure determined in our study is in general agreement with that observed in previous high-pressure experiments. The slope, dP/dT, of the transition determined in our study is consistent with that calculated from calorimetry data.

We found a new nickel sulfide that is isostructural with Fe3S. The synthesized nickel sulfide is a non-stoichiometric compound with a Ni deficiency and its composition is Ni2.90±0.5S. In situ synchrotron X-ray observations indicate that Ni3–xS forms above 5.1 GPa and melts incongruently into Ni+liquid up to 10 GPa. The bulk modulus of Ni3–xS at 300 K was determined to be 140 ± 2 GPa with a fixed K ′ = 4 by static compression with a liquid pressure medium. The eutectic point of the Ni-NiS system lies between Ni3S and Ni3S2 up to 10 GPa and its composition changes from Ni66.6S33.4 at 0.1 MPa to Ni70.7S29.3 at 10 GPa. The eutectic melting temperature of the Ni-NiS system decreases to 5.1 GPa and 720 K as the pressure increases where Ni and α-Ni3S2 are the eutectic solids. On the other hand, the eutectic melting temperature increases with a positive slope above 5.1 GPa where Ni3S+α-Ni3S2 is stable under subsolidus conditions. Intermediate compounds appear at a lower pressure in the Ni-NiS system than that for the Fe-FeS system. Ni3S2 is stable at atmospheric pressure and Ni3S forms at 5.1 GPa, whereas Fe3S2 and Fe3S form at 14 and 20 GPa, respectively. The addition of Ni complicates the melting relationship in the Fe-FeS system at high pressure because of the wider stability field of Ni3S. The low-melting temperature of the Fe-Ni-S system plays an important role in the percolative core-formation of planetesimals during planetary accretion.

An x-ray diffraction measurement and a density functional theory (DFT) calculation of the pressure-induced transformation in LiBH4 were performed. The structure of its first high pressure phase at room temperature (phase-III) was determined to be I41/acd structure, whose unit cell was a √ 2 ×√ 2 ×2 supercell of Ama2 structure proposed previously. Pressure-induced transformation from phase-III took place at 16 GPa and the structure of the second high-pressure phase was analyzed as I4/mmm structure (phase-V′), in which hydrogen atoms were disordered. However, an annealing treatment for phase-V′ under high-pressure suggested that it was a metastable phase. With the pressure elevated up to 30 GPa, the tetragonal I4/mmm structure was gradually transformed to a cubic Fm3m structure, which has been reported as a stable phase of phase-V previously. The P-T diagram was examined using high-pressure/high-temperature Raman scattering, and pressure/temperature dependence of the relative ionic conductivity was observed across the phase boundaries.

Density and seismic velocities of the chromitite bodies from the Oman ophiolite were calculated and compared with those of oceanic peridotites. The Oman chromitite is composed of olivine and chromian spinel, and the olivine/spinel volume ratio varies from 20 to 90 vol%. Chromian spinel in the chromitite is enriched in magnesiochromite component, and Fo content of olivine ranges from 94 to 96. Compressibility of a natural chromian spinel [(Mg 0.77 Fe 2+ 0.23 )(Cr 0.46 Al 0.50 Fe 3+ 0.04 )O 4 ] was measured with in situ synchrotron X-ray diffraction experiments, using a diamond anvil cell up to 10 GPa at 300 K. The third-order Birch-Murnaghan equation of state yields the isothermal bulk modulus of K T = 192(7) GPa, its pressure derivative of K T ′ = 4(1), and the zero-pressure volume of V 0 = 560.6(2) A 3 . Based on calculations using present and previous studies, the adiabatic bulk modulus of magnesiochromite component was estimated to be 189 GPa. Using petrological and the mineral physics data, density and seismic velocities ( V φ , V P , V S ) were calculated. The seismic velocities are higher than those of peridotites in the oceanic upper mantle and decrease with decrease of the spinel/olivine ratio. The contrast between chromitite and oceanic peridotite are 5.0–8.1% for V φ , 2.7–4.9% for V S , and 4.1–6.7% for V P in the Moho transition zone chromitite, and 2.6–6.5% for V φ , 1.4–3.3% for V S , and 2.2–5.2% for V P in the discordant mantle chromitite. This contrast is large enough to be detected by seismological observations and becomes a key to knowing the distributions of chromitite in the oceanic upper mantle.

The viscosity of a silicate melt of composition NaAlSi2O6 was measured at pressures from 1.6 to 5.5 GPa and at temperatures from 1,350 to 1,880°C. We employed in situ falling sphere viscometry using X-ray radiography. We found that the viscosity of the NaAlSi2O6 melt decreased with increasing pressure up to 2 GPa. The pressure dependence of viscosity is diminished above 2 GPa. By using the relationship between the logarithm of viscosity and the reciprocal temperature, the activation energies for viscous flow were calculated to be 3.7 ± 0.4 × 102 and 3.7 ± 0.5 × 102 kJ/mol at 2.2 and 2.9 GPa, respectively.

Lattice-preferred orientations (LPOs) of post-perovskite (PPv)-type MgGeO 3 formed by transformations from two different pre-phases, orthopyroxene (OPx) and perovskite (Pv), were studied using radial and axial X-ray diffraction techniques combined with a laser-heated diamond-anvil cell. When the PPv was made from Pv, strong LPO was formed in the PPv immediately after the transformation with an alignment of the (0 0 1) or (0 1 1) plane almost perpendicular to the compression axis. This present result contrasts markedly from that observed when the PPv was formed from OPx and those reported on MgGeO 3 -PPv and (Mg,Fe)SiO 3 -PPv transformed from OPx, in which the (1 0 0) or (1 1 0) plane was aligned to the compression axis. It was clarified that when the PPv-type MgGeO 3 is formed in diamond-anvil cells, it has strong transformation-induced LPO from the beginning even before plastic deformation occurs, and that its characteristics depend on the pre-phase before the transformation. The formed transformation-induced LPO of PPv did not change in spite of further compression using a conventional gasket because the sample became too thin to deform. However, by using a diamond gasket technique, we were able to deform the PPv at room temperature, resulting in significant variations of the relative intensities of several diffraction peaks. The change in the axial diffraction patterns can be explained only by assuming that the (0 0 1) plane aligns almost perpendicularly to the compression axis. The present results suggest that the (0 0 1) is a dominant slip plane in MgGeO 3 -PPv at room temperature. If one makes the assumption that the dominant slip system(s) of silicate PPv deformed in the D″ layer is or are identical to that of germanate PPv at room temperature, then a large S-wave polarization anisotropy in the Earth's D″ layer would be explained by the small degree of deformation-induced LPO of the PPv phase that is expected to exist in this layer.

High-pressure experiments and ab initio calculations on the hexagonal close-packed (hcp) structure of pure iron were performed to investigate a pressure-induced magnetic transition and the equation of state in the pressure range of 0–107 and 0–400 GPa, respectively. The experimental data at room temperature showed a significant change in the cell parameter ratio at 55 GPa without any major structural changes occurring. Ab initio calculations at 0 K indicate that the change in the cell parameter ratio observed in the high-pressure experiments corresponds to a magnetic transition from an antiferromagnetic state to a nonmagnetic state. If the hcp-Fe is stable under inner core conditions, then the density of nonmagnetic hcp-Fe is ~6% denser than that of the inner core, as determined using the PREM model. This supports the view that the composition of the inner core should be composed of iron and a significant amount of lighter elements.

The collision history of asteroids in the early Solar System is difficult to reconstruct. A study of plagioclase breakdown using X-ray diffraction measurements under increasing pressures and temperatures suggests that peak pressures in collisions that formed shocked meteorites have been overestimated. Shocked meteorites that were formed when their parent body underwent shock metamorphism often contain the mineral plagioclase either in an amorphous form or in its high-pressure phase. The peak pressures in shock metamorphism can be constrained by shock-recovery experiments that determine the amorphization pressures of plagioclase1,2,3. However, in these experiments temperatures have been unrealistically low and timescales much shorter than those in natural events. Here we present in situ X-ray diffraction measurements of two kinds of plagioclase feldspar in conditions of increasing pressures and temperatures. We find that the amorphization pressure of plagioclase decreases with increasing temperature, suggesting that previous studies overestimated this parameter1,2,3. We also found that the mineral jadeite forms first from amorphous plagioclase, whereas the nucleation of other minerals such as stishovite or garnet is significantly delayed. The occurrence of jadeite in shocked meteorites that do not contain stishovite4,5,6,7,8 can therefore be explained as a result of the crystallization kinetics. We conclude that the study of plagioclase breakdown can constrain the pressure–temperature–time history of shock events, and thus help to reconstruct the collisional history of asteroids in the early Solar System.

The stability and equation of state for the cotunnite phase in TiO2 were investigated up to a pressure of about 70 GPa by high-pressure in situ X-ray diffraction measurements using a laser-heated diamond anvil cell. The transition sequence under high pressure was rutile → α-PbO2 phase → baddeleyite phase → OI phase → cotunnite phase with increasing pressure. The cotunnite phase was the most stable phase at pressures from 40 GPa to at least 70 GPa. The equation of state parameters for the cotunnite phase were established on the platinum scale using the volume data at pressures of 37–68 GPa after laser annealing, in which the St value, an indicator of the magnitude of the uniaxial stress component in the samples, indicates that these measurements were performed under quasi-hydrostatic conditions. The third-order Birch-Murnaghan equation of state at K 0′ = 4.25 yields V 0 = 15.14(5) cm3/mol and K 0 = 294(9), and the second-order Birch-Murnaghan equation of state yields V 0 = 15.11(5) cm3/mol and K 0 = 306(9). Therefore, we conclude that the bulk modulus for the cotunnite phase is not comparable to that of diamond.

Fe-Mg partitioning between perovskite and ferropericlase in the MgO-FeO-SiO 2 system has been studied up to about 100 GPa at around 2000 K using a laser-heated diamond anvil cell (LHDAC). The compositions of both phases were determined by using analytical transmission electron microscopy (ATEM) on the recovered samples. Present results reveal that the Fe-Mg apparent partition coefficient between perovskite and ferropericlase [ K D Pv/Fp = ( X Fe Pv X Mg Fp )/( X Mg Pv X Fe Fp )] decreases with increasing pressure for a constant FeO of the system, and it decreases with increasing FeO content of ferropericlase. The gradual decrease of K D Pv/Fp with increasing pressure is consistent with the spin transition in ferropericlase occurring in the broad pressure range from 50 to 100 GPa at around 2000 K.