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The role of stishovite in transporting water in subducting slabs has been a subject of debate for several decades. Here we investigated stishovite's water solubility and its potential role in water transportation as a function of temperature from 1300 to 2100°C at 22 GPa. Under water‐saturated conditions, high‐quality, Al‐free stishovite single crystals were synthesized with multi‐anvil press, and their water contents were measured using infrared spectroscopy. The H2O solubility in stishovite increases from 128(20) to 521(47) wt. ppm with increasing temperature from 1300 to 1700°C and decreased to 145(26) wt. ppm at 2100°C. The maximum H2O content was about seven times larger than earlier high‐temperature multi‐anvil studies but significantly lower than recent laser‐heated diamond anvil cell and low‐temperature multi‐anvil studies. We suggest that Al‐free stishovite may not be a significant H2O carrier in subducting slabs, at least at the topmost lower mantle corresponding to our experimental conditions. Plain Language Summary: Stishovite is a high‐pressure phase of silicon dioxide (SiO2). It was recently reported that stishovite could contain a substantial amount of water based on diamond anvil cell experiments and, consequently, transport water into the lower mantle through subducting slabs. However, the water contents in their samples lack precise constrain due to the limited size of the recovered crystals, making them inaccessible for measurements using reliable FTIR spectroscopy or secondary‐ion mass spectroscopy. To settle this debate, we produced high‐quality single crystals of stishovite under water‐saturated conditions at high pressures and temperatures and measured their water contents using infrared spectroscopy. We discovered that stishovite contained only several hundred ppm of water under conditions at the top of the lower mantle. Therefore, it is likely that stishovite does not contain much water in the upper region of the lower mantle and does not transport water into the deep lower mantle. Key Points: H2O content in Al‐free stishovite increases with temperature up to 1700°C and decreases beyond this temperatureThe maximum H2O content in Al‐free stishovite at 22 GPa is 521 (47) wt. ppmAl‐free stishovite cannot be the major H2O carrier at least up to the uppermost lower mantle conditions [ABSTRACT FROM AUTHOR]

We report the first oxynitride of tin, Sn2N2O (SNO), exhibiting a Rh2S3‐type crystal structure with space group Pbcn. All Sn atoms are in six‐fold coordination, in contrast to Si in silicon oxynitride (Si2N2O) and Ge in the isostructural germanium oxynitride (Ge2N2O), which appear in four‐fold coordination. SNO was synthesized at 20 GPa and 1200–1500 °C in a large volume press. The recovered samples were characterized by synchrotron powder X‐ray diffraction and single‐crystal electron diffraction in the TEM using the automated diffraction tomography (ADT) technique. The isothermal bulk modulus was determined as Bo=193(5) GPa by using in‐situ synchrotron X‐ray diffraction in a diamond anvil cell. The structure model is supported by DFT calculations. The enthalpy of formation, the bulk modulus, and the band structure have been calculated. [ABSTRACT FROM AUTHOR]

A new furnace system with an almost zero temperature gradient throughout the sample area was designed for multi-anvil high pressure experiments. Test experiments of the new design were performed using 18/11 and 25/15 cell assemblies at 4 GPa, 1400°C and 1500°C, respectively. The temperature field within the sample capsules appeared to be very homogenous as indicated by Mg2Si2O6-MgCaSi2O6 two-pyroxene thermometry, by direct temperature measurements using two thermocouples within the same assembly, and by distribution of solid and liquid phases in the sample capsule. The temperature gradient is estimated to be <2.4°C/mm over an area of 4 × 5 mm2 within the furnace. It is significantly lower than standard multi-anvil experiments with straight or stepped furnace systems, which are at the levels of 20-200°C/mm. [ABSTRACT FROM AUTHOR]

To determine the phase boundary between the perovskite and post-perovskite structures in MnGeO3, in situ X-ray observations were carried out at pressures of 57-68 GPa and temperatures of 1000-1900 K using the Kawai-type high-pressure apparatus equipped with sintered diamond anvils interfaced with synchrotron radiation. The phase boundary was determined to be P (GPa) = 39.2 + 0.013T (K) based on Tsuchiya's (2003) gold pressure scale. The Clapeyron slope, dP/dT, of 13(+12/-5) MPa/K, determined in the present study is larger that of MgGeO3 and MgSiO3. [ABSTRACT FROM AUTHOR]

Abstract: By applying the numerical tensor analysis proposed by Yoneda and Kubo [Simultaneous determination of mean pressure and deviatoric stress based on numerical tensor analysis: a case study for polycrystalline X-ray diffraction of gold enclosed in a methanol–ethanol mixture. J. Phys.: Condens. Matter 18(2006)S979], we have determined deviatoric stress and mean pressure of polycrystalline MgO compressed in the Kawai-type apparatus. After the compression at room temperature, the mean pressure and the deviatoric stress in MgO were determined as 34.5 and 3.2GPa, respectively. The mean pressure is significantly lower than the nominal pressure of 37.2GPa determined by the conventional pressure determination method. By heating the sample to 1850K with the constant press load, the deviatoric stress dramatically decreased to 0.1GPa with a mean pressure of 34.2GPa at room temperature after the heating. These results show both the importance of stress analysis to determine pressure more accurately and the effectiveness of annealing to reduce deviatoric stress in the sample. [Copyright &y& Elsevier]

Abstract: High pressure generation has been tried by using the Kawai-cell equipped with sintered diamond cubes and the synchrotron radiation at SPring-8. The maximum attainable pressure reached 90.4GPa at 300K based on the Anderson et al. (1989) Au scale. Simultaneously, we investigated the perovskite (Pv)–postperovskite (PPv) transformation in MgGeO3 up to ca. 74GPa and 2200K by means of in situ X-ray diffraction method. Transformation from Pv to PPv was observed at pressures and temperatures higher than 63GPa and 1300K. Both the forward and the reverse reactions were found to be fairly sluggish over the examined temperature range. We determined the phase boundary by passing through the conditions at which either Pv or PPv phase grew and that of coexistence of both the phases, which is expressed by the equation T(K)=177 P(GPa)−9677. Our dP/dT slope of 5.6MPa/K for MgGeO3 is close to the minimum estimate for MgSiO3 and accordingly suggests relatively deeper D″ discontinuity and a high heat flux from the core. We emphasize that the phase boundary completely relies on the pressure scale adopted. [Copyright &y& Elsevier]