2022 HP special volume:Interdisciplinary high pressure science and technology

High pressure science and technology is a vast area of inter-disciplinary research that encompasses the fields of physics,chem-istry,geoscience,and materials science and in which the science of ordinary matter is only a special case under ambient condi-tions.Pressure,the physical variable of force exerted on the chem-ical bonding of a material,directly controls the material’s phys-ical and chemical properties.

Stability and melting behavior of boron phosphide under high pressure

Boron phosphide(BP)has gained significant research attention due to its unique photoelectric and mechanical properties.In this work,we investigated the stability of BP under high pressure using x-ray diffraction and scanning electron microscope.The phase diagram of BP was explored in both B-rich and P-rich environments,revealing crucial insight into its behavior at 5.0 GPa.Additionally,we measured the melting curve of BP from 8.0 GPa to 15.0 GPa.Our findings indicate that the stability of BP under high pressure is improved within B-rich and P-rich environments.Furthermore,we report a remarkable observation of melting curve frustration at 10.0 GPa.This study will enhance our understanding of stability of BP under high pressure,shedding light on its potential application in semiconductor,thermal,and light-transmitting devices.

A novel rapid cooling assembly design in a high-pressure cubic press apparatus

In traditional high-pressure–temperature assembly design, priority has been given to temperature insulation and retention at high pressures.This limits the efficiency of cooling of samples at the end of experiments, with a negative impact on many studies in high-pressure Earth andplanetary science. Inefficient cooling of experiments containing molten phases at high temperature leads to the formation of quench textures,which makes it impossible to quantify key compositional parameters of the original molten phase, such as their volatile contents. Here,we present a new low-cost experimental assembly for rapid cooling in a six-anvil cubic press. This assembly not only retains high heatingefficiency and thermal insulation, but also enables a very high cooling rate (∼600 ℃/s from 1900 ℃ to the glass transition temperature).Without using expensive materials or external modification of the press, the cooling rate in an assembly (∼600 ℃/s) with cube lengths of38.5 mm is about ten times faster than that in the traditional assembly (∼60 ℃/s). Experiments yielding inhomogeneous quenched melttextures when the traditional assembly is used are shown to yield homogeneous silicate glass without quench textures when the rapid coolingassembly is used.

Recent advances in high-pressure science and technology

Recently we are witnessing the boom of high-pressure science and technology from a small niche field to becoming a major dimension in physical sciences.One of the most important technological advances is the integration of synchrotron nanotechnology with the minute samples at ultrahigh pressures.Applications of high pressure have greatly enhanced our understanding of the electronic,phonon,and doping effects on the newly emerged graphene and related 2D layered materials.High pressure has created exotic stoichiometry even in common Group 17,15,and 14 compounds and drastically altered the basic σ and π bonding of organic compounds.Differential pressure measurements enable us to study the rheology and flow of mantle minerals in solid state,thus quantitatively constraining the geodynamics.They also introduce a new approach to understand defect and plastic deformations of nano particles.These examples open new frontiers of high-pressure research.

Direct hydrogen quantification in high-pressure metal hydrides

compounds showing phonon mediated near room-temperature superconductivity.However,severe limitations in determining the chemical formula of the reaction products,especially with regards to their hydrogen content,impedes a deep understanding of the synthesized phases and can lead to significantly erroneous conclusions.Here,we present a way to directly access the hydrogen content of MH solids synthesized at high pressures in(laser-heated)diamond anvil cells using nuclear magnetic resonance spectroscopy.We show that this method can be used to investigate MH compounds with a wide range of hydrogen content,from MH_(x) with x=0.15(CuH_(0.15))to x■6.4(H_(6±0.4)S_(5)).

In situ high-pressure wide-angle hard x-ray photon correlation spectroscopy:A versatile tool probing atomic dynamics of extreme condition matter

With the advent of new synchrotron radiation x-ray sources that provide a significantly enhanced coherent flux,high-energy x-ray photon correlation spectroscopy measurements can be performed on materials in a diamond anvil cell.Essential information on atomic dynamics that was previously inaccessible can be obtained for various novel phenomena emerging under extreme conditions.This article discusses the importance,feasibility,and experimental details of this technique,as well as the opportunities that it offers to address critical scientific challenges.

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

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.

2020-Transformative science in the pressure dimension

Materials transform abruptly under compression,with their properties varying as strong functions of pressure.Advances in highpressure and probe technology have enabled experimental characterizations up to several hundred gigapascal(GPa).Studies in the physical sciences are now expanding to include a vast previously uncharted pressure region in which transformative ideas and discoveries are becoming commonplace.Matter and Radiation under Extremes(MRE)is taking advantage of this opportunity to provide a forum for publishing the finest peer-reviewed research in highpressure science and technology on the basis of its interdisciplinary interest,importance,timeliness,and surprising conclusions.This MRE HP Special Volume gathers together a set of contemporary perspectives,highlights,reviews,and research articles in multiple disciplines of high-pressure physics,chemistry,materials,and geoscience that illustrate both current and forthcoming trends in this exciting research area.

Geomimicry—Liberating high-pressure research by encapsulation

High pressures induce changes of properties and structures that could greatly impact materials science if such changes were preserved for ambient applications.Mimicking 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.

Effects of catalyst height on diamond crystal morphology under high pressure and high temperature

The effect of the catalyst height on the morphology of diamond crystal is investigated by means of temperature gradient growth(TGG) under high pressure and high temperature(HPHT) conditions with using a Ni-based catalyst in this article. The experimental results show that the morphology of diamond changes from an octahedral shape to a cuboctahedral shape as the catalyst height rises. Moreover, the finite element method(FEM) is used to simulate the temperature field of the melted catalyst/solvent. The results show that the temperature at the location of the seed diamond continues to decrease with the increase of catalyst height, which is conducive to changing the morphology of diamond. This work provides a new way to change the diamond crystal morphology.

Recent progress on high-pressure and hightemperature studies of fullerenes and related materials

Polymerization of fullerenes is an interesting topic that has been studied for almost three decades.A rich polymeric phase diagram of C60 has been drawn under a variety of pressure P and temperature T conditions.Knowledge of the targeted preparation and structural control of fullerene polymers has become increasingly important because of their utility in producing novel fullerenebased architectures with unusual properties and potential applications.This paper focuses on the polymeric phases of fullerenes and their derivatives under high P and/or high T.First,the polymerization behavior and the various polymeric phases of C60 and C70 under such conditions are briefly reviewed.A summary of the polymerization process of intercalated fullerenes is then presented,and a synthetic strategy for novel structural and functional fullerene polymers is proposed.Finally,on the basis of the results of recent research,a proposal is made for further studies of endohedral fullerenes at high P.

Electronic and optical properties of lithium niobate under high pressure: A first-principles study

We theoretically study the structural, electronic, and optical properties of lithium niobate under pressure using the plane-wave pseudopotential density functional theory by CASTEP code. It was found that there is a phase transition from the R3 c structure to the Pnma structure at a pressure of 18.7 GPa. The Pnma structure was dynamically stable according to the calculation of phonon dispersion. From the charge density distributions, there exist covalent interactions along the Nb–O bond. The hybridization between O 2p and Nb 4d orbital in the Pnma phase increases with increasing pressure, while it is not changed in the R3 c phase. With increasing pressure, the average Nb–O bond length decreases and the Nb–O bond population increases, indicating the increased covalent character between Nb and O atoms under high pressure at Pnma phase, which leads to the increased hybridization between O 2p and Nb 4d orbitals. Furthermore, the optical dielectric function, refractive index, extinction coefficient, electron energy, loss and reflectivity are calculated.

Synchrotron-based infrared microspectroscopy under high pressure:An introduction

Synchrotron sources with high photon flux,small source size,and broad energy range have revolutionized ultrafine characterization of condensed matter.With the addition of the pressure dimension realized by the use of diamond anvil cells,enormous progress has been achieved throughout high-pressure science.This is particularly so for synchrotron-based infrared microspectroscopy(SIRMS)with its very high signal-tonoise ratio,high spatial resolution,and extended measurement conditions.SIRMS has high sensitivity,providing a platform for the investigations of the very small amounts of material that need to be used in high-pressure research.This review summarizes developments in SIRMS,focusing on instrumentation and high-pressure measurements.Applications to measurements of infrared reflectance and absorption are presented,illustrating how SIRMS results play a crucial role in advancing understanding of the crystalline phase transitions,electronic transitions,metallization,lattice dynamics,superconductivity,and novel functional behavior.New insights into spectroscopic properties,together with some cutting edge issues and open problems,are also briefly discussed.

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

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 solids.In particular,the model enabled the derivation of a numerical relation between the elastic moduli and the Raman-active F2g mode for diamond.Here,we establish a relation between the diamond Raman frequencyωand the bulk modulus K through first-principles calculation,rather than extrapolation.The calculated K exhibits a combined uncertainty of less than 5.4%compared with the results obtained from the analytical equation of the VFM.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 diamond.Our 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.

Synchrotron X-Ray Diffraction Studies on the New Generation Ferromagnetic Semiconductor Li(Zn,Mn)As under High Pressure

The pressure effect on the crystalline structure of the Ⅰ-Ⅱ-Ⅴ semiconductor Li(Zn,Mn)As ferromagnet is studied using in situ high-pressure x-ray diffraction and diamond anvil cell techniques. A phase transition starting at ~11.6 GPa is found. The space group of the high-pressure new phase is proposed as Pmca. Fitting with the Birch-Murnaghan equation of state, the bulk modulus B_0 and its pressure derivative B_0~' of the ambient pressure structure with space group of F43m are B_0 = 75.4 GPa and B_0~'= 4.3, respectively.

In situ high-pressure nuclear magnetic resonance crystallography in one and two dimensions

Recent developments in in situ nuclear magnetic resonance(NMR)spectroscopy under extreme conditions have led to the observation of a wide variety of physical phenomena that are not accessible with standard high-pressure experimental probes.However,inherent di-or quadrupolar line broadening in diamond anvil cell(DAC)-based NMR experiments often limits detailed investigation of local atomic structures,especially if different phases or local environments coexist.Here,we describe our progress in the development of high-resolutionNMRexperiments in DACs using one-and two-dimensional homonuclear decoupling experiments at pressures up to the megabar regime.Using this technique,spectral resolutions of the order of 1 ppm and below have been achieved,enabling high-pressure structural analysis.Several examples are presented that demonstrate the wide applicability of this method for extreme conditions research.

Structural transitions of 4:1 methanol–ethanol mixture and silicone oil under high pressure

A 4:1(volume ratio)methanol–ethanol(ME)mixture and silicone oil are two of the most widely used liquid pressure-transmitting media(PTM)in high-pressure studies.Their hydrostatic limits have been extensively studied using various methods;however,the evolution of the atomic structures associated with their emerging nonhydrostaticity remains unclear.Here,we monitor their structures as functions of pressure up to∼30 GPa at room temperature using in situ high-pressure synchrotron x-ray diffraction(XRD),optical micro-Raman spectroscopy,and ruby fluorescence spectroscopy in a diamond anvil cell.No crystallization is observed for either PTM.The pressure dependence of the principal diffraction peak position and width indicates the existence of a glass transition in the 4:1MEmixture at∼12 GPa and in the silicone oil at∼3 GPa,beyond which a pressure gradient emerges and grows quickly with pressure.There may be another liquid-to-liquid transition in the 4:1 ME mixture at∼5 GPa and two more glass-to-glass transitions in the silicone oil at∼10 GPa and∼16 GPa.By contrast,Raman signals only show peak weakening and broadening for typical structural disordering,and Raman spectroscopy seems to be less sensitive than XRD in catching these structural transitions related to hydrostaticity variations in both PTM.These results uncover rich pressure-induced transitions in the two PTM and clarify their effects on hydrostaticity with direct structural evidence.The high-pressure XRD and Raman data on the two PTM obtained in this work could also be helpful in distinguishing between signals from samples and those from PTM in future high-pressure experiments.

Engineering HOF‑Based Mixed‑Matrix Membranes for Efficient CO_(2) Separation

Hydrogen-bonded organic frameworks(HOFs)have emerged as a new class of crystalline porous materials,and their application in membrane technology needs to be explored.Herein,for the first time,we demonstrated the utilization of HOF-based mixed-matrix membrane for CO_(2) separation.HOF-21,a unique metallo-hydrogen-bonded organic framework material,was designed and processed into nanofillers via amine modulator,uniformly dispersing with Pebax polymer.Featured with the mix-bonded framework,HOF-21 possessed moderate pore size of 0.35 nm and displayed excellent stability under humid feed gas.The chemical functions of multiple binding sites and continuous hydrogen-bonded network jointly facilitated the mass transport of CO_(2).The resulting HOF-21 mixed-matrix membrane exhibited a permeability above 750 Barrer,a selectivity of~40 for CO_(2)/CH_(4) and~60 for CO_(2)/N_(2),surpassing the 2008 Robeson upper bound.This work enlarges the family of mixed-matrix membranes and lays the foundation for HOF membrane development.

High-pressure structural properties of tetramethylsilane

High-pressure structural properties of tetramethylsilane are investigated by synchrotron powder x-ray diffraction at pressures up to 31.1 GPa and room temperature. A phase with the space group of Pnma is found to appear at 4.2 GPa. Upon compression, the compound transforms to two following phases: the phase with space groups of P2_1/c at 9.9 GPa and the phase with P2/m at 18.2 GPa successively via a transitional phase. The unique structural character of P2_1/c supports the phase stability of tetramethylsilane without possible decomposition upon heavy compression. The appearance of the P2/m phase suggests the possible realization of metallization for this material at higher pressure.