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Yi-Gang Xu: the Earth's deep interior holds the key to habitability

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National Science Review 2021年第4期8卷 35-38页

作者： Jin Liu ho-kwang mao the Center for High Pressure Science and Technology Advanced Research (HPSTAR) HPSTAR

The deep Earth is the engine of whole Earth systems and plays a key role in surface evolution and geological hazards. Scientists have been deciphering the internal processes that shape our habitable planet, especially since the formulation of plate tectonics theory. To date, how the deep Earth works remains mysterious. At the end of 2020,

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Deep Volatiles as the Key for Energy and Environments of the Four-Dimensional Earth System

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Engineering 2019年第3期5卷 393-394页

作者： ho-kwang mao Craig M. Schiffries Center for High Pressure Science and Technology Advanced Research (HPSTAR) Shanghai 201203 China Geophysical Laboratory Carnegie Institution for Science Washington DC 20015 USA

Carbon, hydrogen, oxygen, nitrogen, sulfur, and their compounds are volatile components that dominate the thin and fragile atmosphere, hydrosphere, and biosphere on Earth’s habitable surface. however, the vast majority of these volatiles are hidden in the deep interior, where the high pressure–temperature conditions drastically and categorically alter the physics and chemistry of the volatiles. Like the bloodstream of an organism, the circulations and interactions of volatiles in the deep Earth modulate climate, resources, energy, natural hazards, and other factors that define the Earth as a unique living and changing planet.

关键词： Four-Dimensional Earth System Deep Volatiles

Development of High-Pressure Multigrain X-Ray Diffraction for Exploring the Earth’s Interior

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Engineering 2019年第3期5卷 441-447页

作者： Li Zhang hongsheng Yuan Yue Meng ho-kwang mao Center for High Pressure Science and Technology Advanced Research (HPSTAR) Shanghai 201203 China HPCAT X-Ray Science Division Argonne National Laboratory Argonne IL 60439 USA Geophysical Laboratory Carnegie Institution of Washington Washington DC 20015 USA

The lower mantle makes up more than a half of our planet’s volume. Mineralogical and petrological experiments on realistic bulk compositions under high pressure–temperature (P–T) conditions are essential for understanding deep mantle processes. Such high P–T experiments are commonly conducted in a laser-heated diamond anvil cell, producing a multiphase assemblage consisting of 100 nm to submicron crystallite grains. The structures of these lower mantle phases often cannot be preserved upon pressure quenching;thus, in situ characterization is needed. The X-ray diffraction (XRD) pattern of such a multiphase assemblage usually displays a mixture of diffraction spots and rings as a result of the coarse grain size relative to the small X-ray beam size (3–5 lm) available at the synchrotron facilities. Severe peak overlapping from multiple phases renders the powder XRD method inadequate for indexing new phases and minor phases. Consequently, structure determination of new phases in a high P–T multiphase assemblage has been extremely difficult using conventional XRD techniques. Our recent development of multigrain XRD in high-pressure research has enabled the indexation of hundreds of individual crystallite grains simultaneously through the determination of crystallographic orientations for these individual grains. Once indexation is achieved, each grain can be treated as a single crystal. The combined crystallographic information from individual grains can be used to determine the crystal structures of new phases and minor phases simultaneously in a multiphase system. With this new development, we have opened up a new area of crystallography under the high P–T conditions of the deep lower mantle. This paper explains key challenges in studying multiphase systems and demonstrates the unique capabilities of high-pressure multigrain XRD through successful examples of its applications.

关键词： High pressure Synchrotron X-ray Multigrain Diamond anvil cell Minerals Petrology Earth’s interior

Chemical transformations of n-hexane and cyclohexane under the upper mantle conditions

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Geoscience Frontiers 2021年第2期12卷 1010-1017页

作者： Xin Yang Yapei Li Yajie Wang Haiyan Zheng Kuo Li ho-kwang mao Center for High Pressure Science and Technology Advanced Research Beijing100094China

Alkanes are an important part of petroleum,the stability of alkanes under extreme conditions is of great significance to explore the origin of petroleum and the carbon cycle in the deep ***,we performed Raman and infrared(IR)spectroscopy studies of n-hexane and cyclohexane under high pressure up to~42 GPa at room temperature(RT)and high temperature(HT).n-Hexane and cyclohexane undergo several phase transitions at RT around 1.8,8.5,18 GPa and 1.1,2.1,4.6,13,30 GPa,respectively,without any chemical *** using resistive heating combined with diamond anvil cell at pressure up to 20 GPa and temperature up to 1000 K,both n-hexane and cyclohexane decompose to hydrogenated graphitic carbon and n-hexane exhibits higher stability than *** results indicate that hydrocarbons tend to dehydrogenate in the upper mantle,and the extension of carbon chains may lead to the formation of some unsaturated compounds and eventually transfer into graphitic products.

关键词： Alkanes High pressure and high temperature Dehydrogenation Hydrocarbon Upper mantle conditions

Mineralogy of the deep lower mantle in the presence of H2O

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National Science Review 2021年第4期8卷 21-28页

作者： Qingyang Hu Jin Liu Jiuhua Chen Bingmin Yan Yue Meng Vitali B.Prakapenka Wendy L.mao ho-kwang mao Center for High Pressure Science and Technology Advanced Research(HPSTAR) Department of Geological Sciences Stanford University Center for Study of Matter under Extreme Conditions Department of Mechanical and Materials Engineering Florida International University High Pressure Collaborative Access Team(HPCAT) X-ray Science Division Argonne National Laboratory Center for Advanced Radiation Sources University of Chicago

Understanding the mineralogy of the Earth's interior is a prerequisite for unravelling the evolution and dynamics of our planet. Here, we conducted high pressure-temperature experiments mimicking the conditions of the deep lower mantle（DLM, 1800–2890 km in depth） and observed surprising mineralogical transformations in the presence of water. Ferropericlase,（Mg,Fe）O, which is the most abundant oxide mineral in Earth, reacts with H;2;O to form a previously unknown（Mg,Fe）O;2;H;x;（x ≤ 1）phase. The（Mg,Fe）O;2;H;x;has a pyrite structure and it coexists with the dominant silicate phases,bridgmanite and post-perovskite. Depending on Mg content and geotherm temperatures, the transformation may occur at 1800 km for(Mg;0.6;Fe;0.4;)O or beyond 2300 km for(Mg;0.7;Fe;0.3;)O. The（Mg,Fe）O;2;H;x;is an oxygen excess phase that stores an excessive amount of oxygen beyond the charge balance of maximum cation valences(Mg;2+;, Fe;3+;and H;+;). This important phase has a number of far-reaching implications including extreme redox inhomogeneity, deep-oxygen reservoirs in the DLM and an internal source for modulating oxygen in the atmosphere.

关键词： lower mantle water-mantle interaction ferropericlase high pressure mantle mineralogy

Pressure-induced hydrogen-dominant high-temperature superconductors

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National Science Review 2024年第7期11卷 14-16页

作者： ho-kwang mao Shanghai Advanced Research in Physical Sciences Center for High Pressure Science and Technology Advanced Research

Recent studies of hydrogen-dominant（superhydride） materials have led to putative discoveries of near-room temperature superconductivity at high pressures. The idea started more than half-a-century ago as a by-product of the quest for metallic hydrogen for which a natural consequence of its very high Debye temperature and phonon frequency due to the very low mass of the hydrogen atoms would lead to a high superconducting critical temperature （Tc） in weak coupling Bardeen-Cooper-Schrieffer（BCS） expression.

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Born’s valence force-field model for diamond at terapascals: Validity and implications for the primary pressure scale

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Matter and Radiation at Extremes 2021年第6期6卷 104-110页

作者： Qingyang Hu ho-kwang mao Center for High Pressure Science and Technology Advanced Research Beijing 100094China

Born’s valence force-field model(VFM)established a theoretical scheme for calculating the elasticity,zero-point optical mode,and lattice dynamics of diamond and diamond-structured *** particular,the model enabled the derivation of a numerical relation between the elastic moduli and the Raman-active F2g mode for ***,we establish a relation between the diamond Raman frequencyωand the bulk modulus K through first-principles calculation,rather than *** calculated K exhibits a combined uncertainty of less than 5.4%compared with the results obtained from the analytical equation of the *** results not only validate Born’s classic model but also provide a robust K–ωfunctional relation extending to megabar pressures,which we use to construct a primary pressure scale through Raman spectroscopy and the crystal structure of *** computations also suggest that currently used pressure gauges may seriously overestimate pressures in the multi-megabar regime.A revised primary scale is urgently needed for such ultrahigh pressure experiments,with possible implications for hot superconductors,ultra-dense hydrogen,and the structure of the Earth’s core.

关键词： valence gauge elasticity

Dense hydrous silica carrying water to the deep Earth and promotion of oxygen fugacity heterogeneity

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Matter and Radiation at Extremes 2022年第6期7卷 76-78页

作者： Yanhao Lin ho-kwang mao Center for High Pressure Science and Technology Advanced Research Beijing 100193People’s Republic of China

Water has remarkable effects on the properties of mantle rocks,but,owing to the high temperatures in the mantle,uncertainties remain about how and how much water is transported into the deep *** studies have shown that stishovite and post-stishovites as highpressure phases of SiO2 have the potential to carry weight percent levels of water into the Earth’s interior along the geotherm of the subducting oceanic *** slabs are subducted to the deepest mantle,dehydration of these dense hydrous silica phases has the potential to change the physicochemical properties of the mantle by reducing melting points,forming new high-pressure phases,and enhancing the oxygen fugacity heterogeneity of the lower mantle.

关键词： Earth mantle silica

Geomimicry—Liberating high-pressure research by encapsulation

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Matter and Radiation at Extremes 2022年第6期7卷 79-81页

作者： ho-kwang mao Wendy L.mao Center for High Pressure Science and Technology Advanced Research 10 Dongbeiwang West RoadHaidianBeijing 100094China Department of Geological Sciences Stanford UniversityStanfordCalifornia 94305USA

High pressures induce changes of properties and structures that could greatly impact materials science if such changes were preserved for ambient *** the geological process of diamond formation that the pressures and high-pressure phases in diamond inclusions can be preserved by the strong diamond envelope,we discuss the perspectives that such process revolutionizes high-pressure science and technology and opens a great potential for creation of functional materials with extremely favorable properties.

关键词： properties ambient process