Mg-Fe substitution is most commonly seen in natural solid solution minerals. High resolution X-ray spectroscopy has recently demonstrated that the major lower mantle (LM) minerals undergo a high-to-low spin transition at LM pressures (23-135 GPa). Previous failures of standard DFT and "LDA+U" approaches to describe this phenomenon have hindered its investigation and consequences of fundamental importance to geophysics, such as heat transport in Earth's mantle. Here, using the latest rotationally invariant first principles formulation of LDA+U with optimized effective U, we report the first successful study of this transition in low solute concentration (Mg(1-x)Fex)O, magnesiumwustite. This is believed to be the second most abundant phase of Earth's LM. This encouraging result appears to open for exploration a new class of problems of enormous significance to deep Earth geophysics

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In situ X-ray diffractions on high-pressure phase of platinum carbide were observed using a laser-heated diamond anvil cell (LHDAC) up to a pressure of 120 GPa with X-rays from a synchrotron radiation source at BL10XU, SPring-8 and BL13A, Photon Factory. The platinum carbide phase was stable at pressures greater than 75 GPa. The structure of platinum carbide has a cubic symmetry with NaCl-type structure.

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Using a multianvil apparatus, high pressure phase relations in NaAlSi3O8 and in the system NaAlSi3O8-KAlSi3O8 were examined up to 24 GPa. Synthesized samples were examined using microfocused and powder X-ray diffraction, and were analyzed with SEM-EDS. At 21-22 GPa and 800-2000 C, NaAlSi2O6 jadeite and stishovite changed to NaAlSiO4 calcium ferrite and stishovite, but NaAlSi3O8 holladite was not observed. Maximum solubility of NaAlSi3O8 in KAlSi3O8 holladite was 40-50 mol% at 1400 C, which was almost the same as 40 mol% at 1000 C. Above results suggest that NaAlSi3O8 hollandite would be stable at higher temperature than 2000 C. This interpretation is consistent with natural observation of NaAlSi3O8-rich hollandite in shocked meteorites.

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Hydrogen has large influence on physical and chemical properties of Earth's constituent minerals such as melting temperature and rheological properties. In order to determine the solubility of water in mantle minerals and estimate how much water is stored in Earth's interior, it is critical to investigate the forms of hydrogen in these minerals under high pressure at the atomistic level. We have investigated structural and vibrational properties of hypothetical fully hydrated wadsleyite (Mg7Si4O14(OH)2) using first principles techniques. Cell parameters and linear compressibilities are good agreement with experiments except a axis. We obtained bulk modulus about 138 GPa (K' = 4.5). Using first principles perturbation theory, we have calculated vibrational properties of hydrous wadsleyite. The O-H stretching vibrational frequencies are 3474, 3483, 3503 and 3505 cm-1.

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We have conducted in situ X-ray diffraction study for determination of the phase boundary of hydrous peridotite and basalt compositions. The slope of the decomposition boundary of ringwoodite under the dry condition is very small around -0.4~-1.3 MPa/K, whereas that for the hydrous peridotite becomes about –2 MPa/K. The garnet-perovskite transformation boundary in hydrous basalt is by about 1.5 GPa lower than that in the dry basalt. Thus, there are no density crossover between hydrous peridotite and basalt components in the slabs. Thus, the basaltic layer can easily penetrate into the lower mantle under the wet conditions.

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We have investigated the stability field of delta-AlOOH, which is high-pressure polymorph of diaspore, using a laser-heated diamond-anvil cell. Delta-AlOOH exists in the recovered samples from the pressure range of 40 to 130GPa, and it seems to decompose into Al2O3+ H2O above 1800K.

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Carbon dioxide and water are the most important volatile constituents in the Earth and they produce drastic changes in the melting phase relations and partial melt composition of the mantle peridotites. Study of the peridotite-CO₂ system is closely related to petrogenesis of kimberlite and diamond. There are a few high pressure mineral inclusions (i.e. majorite garnet and Ca & Mg perovskite) in diamond which suggest that kimberlites may be originated from the transition zone and lower mantle. Several experimental petrologists have studied the kimberlite and basalt-CO₂ systems, however the phase relations and melt compositions in the CO₂-bearing peridotite at high pressures are poorly constrained. Simplified peridotite-CO₂ system (like CMS or CMAS) has been studied at pressures up to 12 GPa (Canil and Scarfe, 1990), whereas complex peridotite-CO₂ systems have investigated only at lower pressures (up to 4 GPa, e.g. Wendlandt and Mysen, 1980). In this work we report the results on the phase relations and melt compositions of a model peridotite-CO₂ system determined at 10-20 GPa and temperature range from 1200 to 2100^oC.Our results show that solidus of carbonated peridotite is consistent with low-pressure data for CMAS-CO₂ system. Liquidus phase at 10-20 GPa is majorite garnet. At 10-15 GPa, crystallization sequence with decreasing temperature is garnet, olivine and clinoenstatite. Magnesite is the most important CO₂-rich phase stable in peridotite and clinoenstatite is an important phase in carbonated peridotite at 10-15 GPa.The partial melts formed by 10-25% melting at 10-20 GPa has high MgO (26-34 wt.%) and FeO (7.0-10.4 wt.%) and low SiO₂ (18-36 wt.%) and Al₂O₃ (0.5-1.3 wt.%) contents. It contains also 6-12 wt.% CaO, 0.6-2.0 wt.% Na₂O and 0.1-0.3 wt.% K₂O. The CO₂ contents in the melts are 14-32 wt.%. SiO₂-poor composition of partial melts is different to the results for melting of anhydrous or water-bearing peridotite. Partial melting of hydrous peridotite produce SiO₂-rich melts, which can be related to komatiite magmas (e.g. Litasov and Ohtani, 2002). The composition of low degree partial melts (10%) in present experiments is close to magnesiocarbonatites, whereas higher degree melting (20-25%) produce melts, which is close to kimberlite magmas.

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The Earth's lower mantle is considered to be composed mainly of (Mg,Fe)SiO3-perovskite and magnesiowüstite, and the iron contents influence their densities and phase relations. Therefore, it is very important to determine the iron contents of these phases in understanding structure and dynamics in the lower mantle. Several workers have studied Fe-Mg partitioning between (Mg,Fe)SiO3-perovskite and magnesiowüstite, but temperature dependence on the partitioning has not been well understood. In this study, we have experimentally determined the partitioning of iron between these two phases and its temperature dependence.We conducted high-pressure experiments using a Kawai type high-pressure apparatus at ~24 GPa, and at 1673-2273K. We used San Carlos olivine with a composition of (Mg0.91Fe0.09)2SiO4 as starting material. After the high presser and temperature runs, the products were examined using SEM, EDS and X-ray diffraction techniques to observe the microstructures, to measure the chemical composition and to identify the phase present, respectively.The partition coefficient defined as KD=(Fe/Mg)Pv/ (Fe/Mg)Mw increased from 0.19 to 0.34, with increasing temperature from 1673-2273K.

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We have observed kinetics of high-pressure decomposition reaction from albite to jadeite and quartz (coesite) by in-situ X-ray diffraction method at 2.8-6.0 GPa and 300-600 degree C. Time-resolved X-ray diffraction data for this transformation were collected every 10-300 seconds. Preliminary results suggest that the reaction occurs at relatively low temperatures around 300 degree C when overpressures from the equilibrium boundary are more than 2 GPa.

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We have calculated electric field gradients (EFG) of various crystals using FPLAPW method. Calculated Cq and asymmetry parameter of oxygen well reproduced experimental NMR data within 5 %, except for hydrogen containing systems. Therefore such calculations allow us to uniquely assign NMR peaks to certain sites with confidence.

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Creep experiments on polycrystalline water ice II with a variety of grain sizes (6-38 micron) have been performed at conditions relevant to planetary interiors (confining pressures of 200-250 MPa and temperatures of 200-220 K). Clear differences in creep behavior have been observed with different grain sizes at constant strain rates of 1.4e-8-4.3e-6 (s-1). The grain-size sensitive creep of ice II demonstrated here plausibly dominates plastic strain at the low stress conditions in the interior of medium- and large-size icy moons of the outer solar system

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A hexagonal perovskite is confirmed in BaSiO3 at 32 GPa. The structure exhibits 9R-type sequence with a space group of R-3m. This is the second example of the hexagonal silicate perovskite followed on SrSiO3 compound. It is interested that the degree of face sharing SiO6 octahedra increases in the structure with increasing effective ionic radii of divalent cations.

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High-temperature and high-pressure Raman spectra of ilmenite-type MgX4+O3 (X=Si, Ge, Ti) have been collected up to 773 K, and 31.3, 22.4 and 12.0 GPa, respectively. Temperature and pressure dependence of the force constant of X-O stretching bands revealed that mechanisms of expansion and compression of XO6 octahedra are different in three ilmenites. The tendency is consistent with thermodynamic stability of three ilmenites. From the Raman frequency shifts with temperature and pressure, intrinsic anharmonic effects on isochoric specific heat were elucidated. The anharmonic effects are related to the Debye temperature of three ilmenites.

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FTIRspectra for synthetic (Si,Ge)-talcs,-serpentines and -chlorites

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In this study, Es80Tp20-Cpxss have been investigated by using X-ray and TOF neutron Rietveld methods to determine site occupancies of Fe3+ and Ti4+ at the octahedral and tetrahedral sites.Es80Tp20-Cpxss was synthesized from oxide mixture at 1240ºC in air for 45 days.X-ray powder data was collected using a RIGAKU RINT automated Bragg-Brentano diffractometer system.A time-of-flight (TOF) powder diffractometer, VEGA, has been operated at the KENS pulsed spallation neutron source. The site occupancies of Fe, Ti and Al at the M1 and T sites, refined by the neutron diffraction data, give following atomic contents at the M1 and T sites: (Fe0.447Al0.554)M1(Al0.646Fe0.354Ti0.200Si0.800)T. Thus, the distribution of Ti in the Es-Tp Cpxss is very different from that expected from ionic radius.

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Topaz-OH (Al2SiO4(OH)2), phase egg (AlSiO3OH) and delta-AlOOH are hydrous phases in the Al2O3-SiO2-H2O system that have been found to be stable at successively higher pressures up to those of the lower mantle, and thus may be important in the siliceous sediments of subducting slab. Although the crystal structures of these phases have been determined by X-ray diffraction, this technique is insensitive to H positions and Al-Si disorder. We have applied 1H, 29Si and 27Al NMR and micro-Raman spectroscopy to gain additional insights. Our study revealed that the octahedral Al-Si distribution in phase egg is partially disordered, which is expected to have a significant effect on its physical and thermodynamic properties and stability field. In addition, these data also suggest the presence of some structural disorder in topaz-OH. Finally, our data support that hydrogen bonding is strong in phase egg and delta-AlOOH, but weak in topaz-OH.

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Structures of shock compressed GeO2 and 80GeO2-20SiO2 glasses were investigated by X-ray diffraction, Raman and IR spectroscopy. Maximum structure changes of these glasses were observed around 20GPa and may be due to increase of three-membered rings of (Si,Ge)O4 tetrahedra. At higher pressure, these structures were annealed by high shock residual temperature and backed to original state. Structural change of 80GeO2-20SiO2 glass occurs at higher shock pressure than GeO2 glass.

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