We investigated the H 2 O‐content dependence of Si self‐diffusion coefficient in Fe‐free wadsleyite using multi‐anvil experiments at pressures of 19–20 GPa, temperatures of 1573–1873 K, and H 2 O‐content ranging from ∼10 to 5,300 wt. ppm by the isotopic thin‐film diffusion‐couple method. The 29 Si‐doped diffusion profiles were measured by nanoscale secondary ion mass spectrometry in the depth profiling mode. The H 2 O contents in the samples were analyzed by Fourier transformation infrared spectroscopy. The experimental results show a H 2 O enhancement of Si diffusion coefficient with a H 2 O content exponent of 0.8 ± 0.1. The activation enthalpy was found to be 270 ± 40 kJ/mol. The diffusion coefficients in the [100], [010], and [001] directions are indistinguishable. The temperature and H 2 O‐content dependences of Si diffusion indicate that H 2 O incorporation dramatically reduces the rheological strength of wadsleyite, whereas temperature has a relatively small effect. The viscosity in the mantle transition zone could be significantly reduced by H 2 O incorporation in wadsleyite. The viscosity contrast between mantle plumes and surroundings may control the evolution of plume shapes at 410–660 km depths.

The mantle transition zone is considered as a potential water reservoir in the Earth's interior because of the high H2O solubility in wadsleyite and ringwoodite. However, this scenario is based on experiments performed under relatively oxidized conditions. In order to constrain the H2O solubility in minerals in the reducing (close to iron-wfistite buffer) mantle transition zone, here we systematically measured the water content in wadsleyite at 17 GPa and 1673 K, as a function of oxygen fugacity in the range of Hf-HfO2, Mo-MoO2, Re-ReO2, and Pt-PtO2 buffer conditions. The results suggest that the oxygen fugacity has no meaningful effect on H2O solubility in wadsleyite. Wadsleyite in the mantle transition zone can store as much as similar to 1.0 wt.% H2O in spite of the reducing conditions. The dissociation of H2O into H-2 and O-2 is negligible, namely, there should be negligible molecular H-2 in the mantle transition zone. (C) 2021 Elsevier B.V. All rights reserved.

High-temperature ionic conductivity in olivine single crystals has been measured in the [100], [010], and [001] crystallographic orientations as a function of pressure from 2 to 10 GPa, temperature from 1450 to 2180 K, and H2O content from 20 to 580 wt. ppm using multianvil presses with in situ impedance analyses. The experimental results yield an activation energy, activation volume, and H2O content exponent of 250-405 kJ/mol, 3.2-5.3 cm(3)/mol, and 1.3 +/- 0.2, respectively, for the high-temperature ionic conduction regime. Olivine ionic conductivity has negative pressure and positive temperature dependences and is significantly enhanced by H2O incorporation. The [001] direction is more conductive than the [100] and [010] directions. The H2O-enhanced ionic conductivity may contribute significantly to the electrical conductivity profile in the asthenosphere, especially in the regions under relatively high-temperature and low-pressure conditions.

This is the supporting materials for the article Water-enhanced ionic conductivity in olivine by Fei et al.

The Earth’s mantle is characterized by a sharp seismic discontinuity at a depth of 660 km that can provide insights into deep mantle processes. The discontinuity occurs over only 2 km—or a pressure difference of 0.1 GPa—and is thought to result from the post-spinel transition, that is, the decomposition of the mineral ringwoodite to bridgmanite plus ferropericlase. Existing high-pressure, high-temperature experiments have lacked the pressure control required to test whether such sharpness is the result of isochemical phase relations or chemically distinct upper and lower mantle domains. Here, we obtain the isothermal pressure interval of the Mg–Fe binary post-spinel transition by applying advanced multi-anvil techniques with in situ X-ray diffraction with the help of Mg–Fe partition experiments. It is demonstrated that the interval at mantle compositions and temperatures is only 0.01 GPa, corresponding to 250 m. This interval is indistinguishable from zero at seismic frequencies. These results can explain the discontinuity sharpness and provide new support for whole-mantle convection in a chemically homogeneous mantle. The present work suggests that distribution of adiabatic vertical flows between the upper and lower mantles can be mapped on the basis of discontinuity sharpness. The post-spinel transition in mantle composition, which occurs at 660-km depth in Earth’s mantle, takes place over a pressure range equivalent to 250 m in depth, according to multi-anvil experiments for realistic mantle compositions and temperatures.

(1) University of Bayreuth , Bayerisches Geoinstitut, Germany, (2) Department of Earth Sciences, Graduate School of Science, Tohoku University, Japan, (3) Department of Earth and Planetary Systems Science, Graduate School of Science, Hiroshima University, Japan, (4) Deutsche Elektronen-Synchrotron, Germany, (5) Institute for Study of the Earth’s Interior, Okayama University, Japan, (6) Japan Synchrotron Radiation Research Institute, Japan

The 660-km seismic discontinuity, which is a significant structure in the Earth’s mantle, is generally interpreted as the post-spinel transition, as indicated by the decomposition of ringwoodite to bridgmanite + ferropericlase. All precise high-pressure and high-temperature experiments nevertheless report 0.5–2 GPa lower transition pressures than those expected at the discontinuity depth (i.e. 23.4 GPa). These results are inconsistent with the post-spinel transition hypothesis and, therefore, do not support widely accepted models of mantle composition such as the pyrolite and CI chondrite models. Here, we present new experimental data showing post-spinel transition pressures in complete agreement with the 660-km discontinuity depth obtained by high-resolution in situ X-ray diffraction in a large-volume high-pressure apparatus with a tightly controlled sample pressure. These data affirm the applicability of the prevailing mantle models. We infer that the apparently lower pressures reported by previous studies are experimental artefacts due to the pressure drop upon heating. The present results indicate the necessity of reinvestigating the position of mantle mineral phase boundaries previously obtained by in situ X-ray diffraction in high-pressure–temperature apparatuses.

We have expanded the pressure ranges at room and high temperatures generated in a Kawai-type multi-anvil apparatus (KMA) using tungsten carbide (WC) anvils with a high hardness of H-v=2700 and a Young's modulus of 660GPa. At room temperature, a pressure of 64GPa, which is the highest pressure generated with KMA using WC anvils in the world, was achieved using 1 degrees-tapered anvils with a 1.5-mm truncation. Pressures of 48-50GPa were generated at high temperatures of 1600-2000K, which are also higher than previously achieved. Tapered anvils make wide anvil gaps enabling efficient X-ray diffraction. The present pressure generation technique can be used for studying the upper part of the Earth's lower mantle down to 1200km depth without sintered diamond anvils.

We have generated over 40 GPa pressures, namely, 43 and 44 GPa, at ambient temperature and 2000 K, respectively, using Kawai-type multi-anvil presses (KMAP) with tungsten carbide anvils for the first time. These high-pressure generations were achieved by combining the following pressure-generation techniques: (1) precisely aligned guide block systems, (2) high hardness of tungsten carbide, (3) tapering of second-stage anvil faces, (4) materials with high bulk modulus in a high-pressure cell, and (5) high heating efficiency.

Paracetamol (p-hydroxyacetanilide, Pbca), acetotoluidine (p-methylacetanilide, P21/c) and methacetin (p-methoxyacetanilide, Pbca) contain acetamide group included in molecular fragments, which play an important role in many drugs and proteins. As all of them are derivatives of acetanilide used in medicine, and due to the presence of the amide bond, their charge density analysis is important for better understanding amide infinite peptide chains. Thus, comparing the data obtained for paracetamol with acetotoluidine and with methacetin charge density data can provide deeper insight into NH···O bonding. Another point of interest is the possibility of methyl group rotation that remains to be ambiguous in these acetanilide molecule based compounds. In the present study we have attempted to elucidate these problems using precise X-ray diffraction at 100K with subsequent charge density topological analysis. All charge density refinements were based on the Hansen and Coppens multipolar atom model. The topologies of the inter- and intramolecular interactions are carefully analyzed for compounds. The atomic charges, bond orders, and the electrostatic energy in molecules are discussed. The topological characteristics in the critical point of the NH···O bond of paracetamol, acetotoluidine and methacetin are shown in the table below. In contrast to similarity in NH···O bonds for all studied compounds, intermolecular interactions between the double bonded oxygen atom and the hydrogen of dimer's methyl group are different. In acetotoluidine and methacetin the (3, –1) critical points with the same topological characteristics were detected between these atoms. In comparison to them, paracetamol with disordered methyl group [1, 2] has no such point. That can be related to the absence of the methyl group disorder in acetotoluidine and methacetin.