High-pressure and high-temperature synthesis of heavy lanthanide sesquisulfides Ln2S3 ( Ln=Yb and Lu)

Detailed pressure-temperature phase diagrams of heavy lanthanide sesquisulfides Ln2S3 (Ln = Yb and Lu) have been investigated by in-situ x-ray diffraction experiments under high pressure and high temperature using synchrotron radiation and multi-anvil press. Based on the results of the in-situ observation, the single γ-phase (Th3P4-type structure, I3d) samples of Ln2S3 (Ln = Yb and Lu) have been synthesized under high pressure. The physical properties of the compounds were studied by electrical resistivity, specific heat, and magnetic susceptibility measurements between 2 K and 300 K

Polycrystalline {\gamma}-boron: As hard as polycrystalline cubic boron nitride

The Vickers hardness of polycrystalline {\gamma}-B was measured using a diamond indentation method. The elastic properties of polycrystalline {\gamma}-B (B=213.9 GPa, G=227.2 GPa, and E=503.3 GPa) were determined using ultrasonic measurement at ambient condition. Under the loading force up to 20 N, our test gave an average Vickers hardness in the asymptotic-hardness region of 30.3 GPa. The average fracture toughness was measured as 4.1MPa m1/2. Additionally, We also measured the hardness and elastic properties of polycrystalline {\beta}-B and PcBN for comparison. The hardness and elastic properties for polycrystalline {\gamma}-B was found to be very close to that of PcBN. Our results suggest that the polycrystalline {\gamma}-B could be a superhard polycrystalline material for industrial applications.Comment: 16 page

高温高圧下におけるエンスタタイトの相転移について

Crystal structures and phase transitions of enstatite (MgSiO3) at high pressures and high temperatures were studied by several methods, including in situ X-ray diffraction experiments using synchrotron radiation and a multi-anvil high pressure apparatus up to 12 GPa and 1200℃, high temperature X-ray diffraction experiments up to 1100℃, X-ray diffraction analyses and transmission electron microscope observations of the quenched samples from high pressure and/or high temperature experiments. High pressure and high temperature in situ X-ray experiments showed that low clinoenstatite with space group P21/c transforms to clinoenstatite with space group C2/c at the wide range of high pressures, accompanied by a volume reduction of about 2.5%. The β angles of this high pressure C2/c phase range from 101.51° to 101.8°at high pressures and high temperatures, being about 8° smaller than those of the high temperatureC2/c phase previously reported. This suggests that a significant structural gap still exists between both C2/c phase. The equations of state for the high-P C2/c and the P21/c phases determined from the P-V data at room temperature using a third-order Birch-Murnaghan equation of state with the fixed K' of 4 give Ka = 84.3(8.3) GPa and Va = 411.1(2.7) A3 GPa for high-P C2/c and Ka = 104.9(3.5) GPa and Va = 415.9 (8) A3 for P21/c, where K'a, Ka, and Va are the pressure derivative of bulk modulus, the isothermal bulk modulus, and the unit-cell volume, respectively at ambient conditions. High temperature powder X-ray diffraction experiments up to 1100℃ suggest that the high temperature C2/c phase exists at temperatures 1060-1100℃, although the different starting materials give different results. The β angles of this high temperature C2/c phase are around 110° at 1100℃, and consistent with the previously reported value and about 80° larger than those of the high pressure C2/c phase. Transmission electron microscopy (TEM) observations of the quenched samples which were synthesized at 8 GPa and 1000℃ and at 1050℃ showed the offsets of the (100) fringes of the P21/c phase by a half of (100) spacing between the neighboring domains across the (100) stacking faults, suggesting that the antiphase domains were formed by the phase transition from the C2/c phase to P21/c phase during the quenching or upon decompression. Piston cylinder apparatus experiments revealed the different phase relations of orthoenstatite depending on the experiments with or without a MgCL2・6H2O fiux. In the experiments with a MgCL2・6H2O flux at 15 kbar, low clinoenstatite inverts to orthoenstatite at temperature as low as 550℃, suggesting that the orthoenstatite and low clinoenstatite equilibrium boundary may shift toward the lower temperature region than previously reported

Effect of chemical environment on the hydrogen-related defect chemistry in wadsleyite

absTracT The effect of chemical environment on the hydrogen-related defect chemistry in wadsleyite was investigated using Fourier-transform infrared (FTIR) spectroscopy. Samples were annealed at P = 14-16 GPa and T = 1230-1973 K using Kawai-type multi-anvil apparatus. The effect of oxygen fugacity (f O 2 ) was investigated using three metal-oxide buffers (Mo-MoO 2 , Ni-NiO, and Re-ReO 2 ). The effect of water fugacity (f H 2 O ) was studied using two different capsule assemblies ("nominally dry" and "dry" assemblies). A range of total OH concentration (C OH,Total ) of studied wadslyeites varies between <50 H/10 6 Si (<3 wt ppm H 2 O) and 23 000 H/10 6 Si (1400 wt ppm H 2 O). The observed FTIR spectra were classified into four different classes, i.e., peaks at 3620 ("3620"), 3480 ("3480"), and 3205 cm -1 ("3205") and the others (Group O), where the Group O includes peaks at 3270, 3330, and 3580 cm −1 . The variation in OH concentration corresponding to each peak was analyzed separately. The OH concentrations correspond to "3620," "3480," and "3205" were found to be highly dependent on both f H 2 O and f O 2 . Assuming , present data were analyzed by using thermodynamic model for concentration of hydrogen-related defects. Based on analytical results, OH concentration of "3620" and "3480" was found to be reasonably explained by q = 1/2 and r = 1/12 (q and r are f H 2 O and f O 2 exponents, respectively), whereas that of "3205" was consistent with q = 1/2 and r = -1/12. These results suggest that "3620" and "3480" correspond to H' M whereas "3205" corresponds to

Temperature dependence of nitrogen solubility in bridgmanite and evolution of nitrogen storage capacity in the lower mantle

International audienceAbstract Relative nitrogen abundance normalized by carbonaceous chondrites in the bulk silicate Earth appears to be depleted compared to other volatile elements. Especially, nitrogen behavior in the deep part of the Earth such as the lower mantle is not clearly understood. Here, we experimentally investigated the temperature dependence of nitrogen solubility in bridgmanite which occupies 75 wt.% of the lower mantle. The experimental temperature ranged from 1400 to 1700 °C at 28 GPa in the redox state corresponding to the shallow lower mantle. The maximum nitrogen solubility in bridgmanite (MgSiO 3 ) increased from 1.8 ± 0.4 to 5.7 ± 0.8 ppm with increasing temperature from 1400 to 1700 °C. The nitrogen storage capacity of Mg-endmember bridgmanite under the current temperature conditions is 3.4 PAN (PAN: mass of present atmospheric nitrogen). Furthermore, the nitrogen solubility of bridgmanite increased with increasing temperature, in contrast to the nitrogen solubility of metallic iron. Thus, the nitrogen storage capacity of bridgmanite can be larger than that of metallic iron during the solidification of the magma ocean. Such a “hidden” nitrogen reservoir formed by bridgmanite in the lower mantle may have depleted the apparent nitrogen abundance ratio in the bulk silicate Earth

Mechanism of pressure induced amorphization of SnI 4 : a combined X-ray diffraction -X-ray absorption spectroscopy study

International audienceWe have studied the amorphization process of SnI 4 up to 26.8GPa with unprecedented experimental details by combining Sn and I K edge X-ray absorption spectroscopy and powder X-ray diffraction. Standards and reverse Monte Carlo extended X-ray absorption fine structure (EXAFS) refinements confirm that the SnI 4 tetrahedron is a fundamental structural unit that is preserved through the crystalline phase-I to crystalline phase-II transition about 7 to 10GPa and then in the amorphous phase that appears above 20GPa. Up to now unexploited Iodine EXAFS reveals to be extremely informative and confirms the formation of iodine iodine short bonds close to 2.85Å in the amorphous phase at 26.8 GPa. A coordination number increase of Sn in the crystalline phase-II appears to be excluded, while the deformation of the tetrahedral units proceeds through a flattening that keeps the average I-Sn-I angle close to 109.5°. Moreover, we put in evidence the impact of pressure on the Sn near edge structure under competing geometrical and electronic effects