Shigeaki Ono

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The Earth's lower mantle is believed to be composed mainly of (Mg,Fe)SiO3 perovskite, with lesser amounts of (Mg,Fe)O and CaSiO3 (ref. 1). But it has not been possible to explain many unusual properties of the lowermost approximately 150 km of the mantle (the D" layer) with this mineralogy. Here, using ab initio simulations and high-pressure experiments, we(More)
1. This mineralogy cannot explain many unusual properties of the D'' layer, the lowermost ~150 km of the mantle. Here, using ab initio simulations and high-pressure experiments we show that at pressures and temperatures of the D'' layer, MgSiO 3 transforms from perovskite into a layered CaIrO 3 –type structure (space group Cmcm). The elastic properties of(More)
In situ observations of the perovskite–CaIrO 3 phase transition in MgSiO 3 and in pyrolitic compositions were carried out using a laser-heated diamond anvil cell interfaced with a synchrotron radiation source. For pure MgSiO 3 , the phase boundary between the orthorhombic Mg-perovskite and CaIrO 3-type phases in the temperature range of 1300–3100 K was(More)
Carbonates are important constituents of marine sediments and play a fundamental role in the recycling of carbon into the Earth's deep interior via subduction of oceanic crust and sediments. Study of the stability of carbonates under high pressure and temperature is thus important for modelling the carbon budget in the entire Earth system. Such studies,(More)
Using ab initio simulations and high-pressure experiments in a diamond anvil cell, we show that alumina (Al(2)O(3)) adopts the CaIrO(3)-type structure above 130 GPa. This finding substantially changes the picture of high-pressure behavior of alumina; in particular, we find that perovskite structure is never stable for Al(2)O(3) at zero Kelvin. The(More)
We have used a laser-heated diamond anvil cell to investigate the stability and compressibility of Cmcm CaIrO 3-type (post-perovskite structure) Al 2 O 3 at pressures up to 200 GPa. A phase transformation from the Pbcn Rh 2 O 3 (II)-type to the CaIrO 3-type structure was observed at 130 GPa, which is consistent with previous theoretical studies. The(More)
Keywords: post-magnesite density functional theory ab initio simulations crystal structure prediction evolutionary algorithm high pressure Most of the oxidized carbon in the Earth's lower mantle is believed to be stored in the high-pressure forms of MgCO 3 and/or CaCO 3 or possibly even CO 2. Recently, through ab initio evolutionary simulations and(More)
Keywords: iron sulfide phase transformation magnetic property high pressure first principles calculation evolutionary crystal structure prediction Iron sulfide (FeS) was investigated using first-principles calculations up to a pressure of 400 GPa. A number of new phase transitions were found. An antiferromagnetic MnP-type structure, FeS II, was confirmed to(More)
The equation of state of tantalum (Ta) has been investigated to 100 GPa and 3,000 K using the first-principles molecular dynamics method. A large volume dependence of the thermal pressure of Ta was revealed from the analysis of our data. A significant temperature dependence of the calculated effective Grüneisen parameters was confirmed at high pressures.(More)
Iron(III) oxide shows a polymorphism, characteristic of existence of phases with the same chemical composition but distinct crystal structures and, hence, physical properties. Four crystalline phases of iron(III) oxide have previously been identified: α-Fe2O3 (hematite), β-Fe2O3, γ-Fe2O3 (maghemite), and ε-Fe2O3. All four iron(III) oxide phases easily(More)