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Our understanding on how opaque materials respond to extreme compression and high temperatures heavily relies on x-ray techniques. While X-ray diffraction is a powerful approach, some properties such as viscosity are experimentally not accessible with such approaches. Application of x-ray imaging has been widely applied in extreme pressure and temperature conditions using multi-anvil presses, but obtaining sufficient space and time resolution for similar experiments using diamond anvil cells, at commensurately higher pressure and temperature conditions, have been challenging. We present recent developments in synchrotron X-ray imaging at the ECB beamline at PETRA III, DESY used in combination with laser heated DAC. Simultaneous X-ray imaging and diffraction allows for deeper insight in properties of materials under high pressure as well as the direct correspondence of phase transition diagnostics. We present a case study of bismuth in the laser-heated diamond anvil cell showing detection of solid-solid and solid-liquid transitions and explore how X-ray imaging can be used to determine viscosity of molten bismuth under pressure.

The observed density of planetary cores is lower than in pure iron-nickel alloy at corresponding conditions. Therefore, the cores of terrestrial planets should be composed of iron-nickel alloyed with some lighter elements. These elements should be abundant in the solar system, siderophile, and compatible with iron at high-pressure high-temperature conditions. Si and C comply with these requirements and could be planetary core constituents. Seismic observations of the Earth's inner core revealed anisotropy of seismic wave propagation. For instance, compressional waves travel 1-3% faster along the polar axis compared to waves travelling in the equatorial plane. One of the hypotheses of the origin of the anisotropy is the plastic deformation and development of textures in inner-core materials under pressure. We employed Fe-Si-C alloy to study its yield strength and anisotropy at high-pressure high-temperature conditions to compare its properties with those observed in the Earth's core. The experiments were conducted by radial X-ray diffraction coupled with resistively heated diamond anvil cells that acted as a deformation apparatus. We performed experiments up to 120 GPa pressure with temperatures exceeding 1100 K. The strength values of Fe-Si-C alloy are higher than the strength of pure Fe and Fe-Si alloys. Our results show lower anisotropy of sound-wave velocities in hexagonal Fe-Si-C alloy compared to the seismic observations. We detected the change in main texture orientation upon compression from [0001] to in Fe-Si-C alloy. In our presentation, we will discuss the dominant mechanisms of plastic deformation, responsible for these observations, and the overall effects of carbon and silicon on the strength and anisotropy of hexagonal iron alloys in planetary cores.

The iron spin crossover in ferropericlase, the second most abundant mineral in Earth’s lower mantle, causes changes in a range of physical properties, including seismic wave velocities. Understanding the effect of temperature on the spin crossover is essential to detect its signature in seismic observations and constrain its occurrence in the mantle. Here, we report the first experimental results on the spin crossover-induced bulk modulus softening at high temperatures, derived directly from time-resolved x-ray diffraction measurements during continuous compression of (Mg0.8Fe0.2)O in a resistive-heated dynamic diamond-anvil cell. We present new theoretical calculations of the spin crossover at mantle temperatures benchmarked by the experiments. Based on our results, we create synthetic seismic tomography models to investigate the signature of the spin crossover in global seismic tomography. A tomographic filter is applied to allow for meaningful comparisons between the synthetic models and data-based seismic tomography models, like SP12RTS. A negative anomaly in the correlation between Vs variations and Vc variations (S-C correlation) is found to be the most suitable measure to detect the presence of the spin crossover in tomographic models. When including the effects of the spin crossover, the misfit between the synthetic model and SP12RTS is reduced by 63%, providing strong evidence for the presence of the spin crossover, and hence ferropericlase, in the lower mantle. Future improvement of seismic resolution may facilitate a detailed mapping of spin state using the S-C correlation, providing constraints on mantle temperatures, thanks to the temperature sensitivity of the spin crossover.

Earth and planetary science letters 604, 118015 (2023). doi:10.1016/j.epsl.2023.118015, The ‘660’ discontinuity is often associated with a phase transitions in pyrolite at about 24 GPa. There are ubiquitous reports of seismic anisotropy below the ‘660’ which are difficult to explain from a mineralogical point of view. In this study, we implement multigrain crystallography X-ray diffraction in the laser-heated diamond anvil cell in order to track microstructures induced by phase transitions at the pressure and temperature conditions of the discontinuity. Before the onset of transformation, garnet is isotropic with ringwoodite displaying a weak 001 texture. After the transformation, bridgmanite displays strong 001 transformation textures which we attribute to growth under stress. Davemaoite exhibits weak maxima in 101 and 111 orientations with ferropericlase displaying no texture. The results are used to model anisotropy in a subducting slab, with a prediction of no anisotropy above the ‘660’ and up to 1.28% (0.08 km/s) shear wave splitting below the ‘660’. In addition, we predict $V_{SV} > V_{SH}$ for horizontally traveling waves and near-vertical subduction and $V_{SV} < V_{SH}$ in the case a slab impinging below the boundary layer., Published by Elsevier, Amsterdam [u.a.]

Magnetite, Fe

We have synthesized the orthocarbonate Sr3[CO4]O in a laser-heated diamond anvil cell at 20 and 30 GPa by heating to ≈3000 (300) K. Afterward, we recovered the orthocarbonate with [CO4]4- groups at ambient conditions. Single-crystal diffraction shows the presence of [CO4]4- groups, i.e., sp3-hybridized carbon tetrahedrally coordinated by covalently bound oxygen atoms. The [CO4]4- tetrahedra are located in a cage formed by corner-sharing OSr6 octahedra, i.e., octahedra with oxygen as a central ion, forming an antiperovskite-type structure. At high pressures, the octahedra are nearly ideal and slightly rotated. The high-pressure phase is tetragonal (I4/mcm). Upon pressure release, there is a phase transition with a symmetry lowering to an orthorhombic phase (Pnma), where the octahedra tilt and deform slightly.

Journal of synchrotron radiation 28(5), 28 (2021). doi:10.1107/S1600577521007335, The European XFEL delivers up to 27000 intense (>1012 photons) pulses per second, of ultrashort (≤50 fs) and transversely coherent X-ray radiation, at a maximum repetition rate of 4.5 MHz. Its unique X-ray beam parameters enable groundbreaking experiments in matter at extreme conditions at the High Energy Density (HED) scientific instrument. The performance of the HED instrument during its first two years of operation, its scientific remit, as well as ongoing installations towards full operation are presented. Scientific goals of HED include the investigation of extreme states of matter created by intense laser pulses, diamond anvil cells, or pulsed magnets, and ultrafast X-ray methods that allow their diagnosis using self-amplified spontaneous emission between 5 and 25 keV, coupled with X-ray monochromators and optional seeded beam operation. The HED instrument provides two target chambers, X-ray spectrometers for emission and scattering, X-ray detectors, and a timing tool to correct for residual timing jitter between laser and X-ray pulses., Published by Wiley-Blackwell, [S.l.]

A gasket is an important constituent of a diamond anvil cell (DAC) assembly, responsible for the sample chamber stability at extreme conditions for X-ray diffraction studies. In this work, we studied the performance of gaskets made of metallic glass Fe

Astrophysical surveys so far have suggested that water-rich planets could be common [1] (including Uranus and Neptune in our Solar System). In the conventional interior model of water-rich planets, it has been assumed to have separate layers of atmosphere, ice/fluid, rocky mantle and metallic core [2]. However, recent studies have proposed the existence of heavy elements in the ice/fluid layer of Uranus, challenging the conventional view [3]. In addition, chemical interaction and thermodynamic processes of major rock-forming minerals at the H2O–rock interface conditions of the water-rich planetary interiors have been scarcely explored. We have performed laser-heated diamond-anvil cell experiments on two rock-forming minerals, olivine ((Mg0.9,Fe0.1)2SiO4) and ferropericlase ((Mg0.9,Fe0.1)O), in water at the pressure and temperature conditions expected for the water-rich planets. During laser-heating, we collected X-ray diffraction (XRD) data at beamlines 13-IDD of GSECARS at APS and P02.2, the ECB of PETRA III at DESY. Our dataset covers pressures between 20 and 80 GPa. After high-pressure and high-temperature experiments, we conducted chemical and textural analysis using focused ion beam (FIB) and scanning electron microscope (SEM) at Yonsei University. During laser-heating, Si-rich high-pressure phases were formed, such as bridgmanite ((Mg,Fe)SiO3) and stishovite (SiO2), from the high Mg/Si ratio of starting composition (olivine). The formation of Si-rich phases from Mg-rich starting composition suggests dissolve of MgO into H2O-liquid during laser-heating at high-pressures. This was also found for (Mg0.9,Fe0.1)O ferropericlase starting material. The intensity of the diffraction peak of ferropericlase was dramatically decreased at high-pressure and high-temperature conditions, which indicates that (Mg0.9,Fe0.1)O is soluble in H2O-liquid. From chemical analysis, we found the dome-like structures, which showed that domes are Mg-rich and below the domes is Si-rich. Between Mg-rich and Si-rich regions, porous structures (almost empty) were positioned, meaning that MgO-rich fluid existed at high-pressure and high-temperature conditions. In summary, the textural and chemical analysis combined with XRD data indicates a selective leaching of MgO preferentially from silicate during laser heating, making MgO-dissolved in high-temperature fluid, which peaks between 20 and 40 GPa and above 1,500 K [4]. For water-rich planets with 1–6 Earth masses, the chemical reaction at the deep H2O–rock interface would lead to high concentrations of MgO in the H2O layer. For Uranus and Neptune, our experiments indicate that the top ~3% of the H2O layer of them, the pressure and temperature conditions of which have been achieved in this study, would have a large storage capacity for MgO. If an early dynamic process enables the H2O–rock reaction, the topmost H2O layer may be rich in MgO, possibly affecting the thermal history of the planet. [1] Batalha, N. M. Proc. Natl Acad. Sci. USA 111, 12647–12654 (2014). [2] Guillot, T. Annu. Rev. Earth Planet. Sci. 33, 493–530 (2005). [3] Helled, R., Nettelmann, N. & Guillot, T. Space Sci. Rev. 216, 38 (2020). [4] Kim, T. et al. Nat. Astron. (2021).

A thin layer with a lower velocity has been documented at the topmost outer core (Eʹ layer). However, the observation has been difficult to explain with a light element concentration change. Here, performing laser-heated diamond anvil cell experiment, we report the formation of FeHx and SiO2 from a reaction between water and FeSi alloy at the conditions relevant to the Earth’s core-mantle boundary (CMB). If water has been delivered to the CMB, this reaction could enable the exchange of hydrogen and silicon between the mantle and the core. As a result, a H-rich, Si-deficient layer formed at the topmost core would have a lower density, stabilizing the stratification, and a lower velocity, consistent with seismic studies. Therefore, the Eʹ layer may result from the deep transport of water to the CMB.

Polynitrides are intrinsically thermodynamically unstable at ambient conditions and require peculiar synthetic approaches. Now, a one-step synthesis of metal-inorganic frameworks Hf4N20 center dot ...

The synthesis of a novel type of carbonate, namely of the inorganic pyrocarbonate salt Sr[C

Physical review / B 105(8), 085155 (2022). doi:10.1103/PhysRevB.105.085155, Iron-bearing carbonates play an important role in Earth's carbon cycle. Owing to their stability at mantle conditions, recently discovered iron carbonates with tetrahedrally coordinated carbon atoms are candidates for carbon storage in the deep Earth. The carbonates' iron oxidation and spin state at extreme pressure and temperature conditions contribute to the redox conditions and element partitioning in the deep mantle. By laser heating FeCO$_3$ at pressures of about 83 GPa, Fe$^{3+}_4$C$_3$O$_{12}$ and Fe$^{2+}_2$Fe$^{3+}_2$C$_4$O$_{13}$ were synthesized and then investigated by x-ray emission spectroscopy to elucidate their spin state, both in situ and temperature quenched. Our experimental results show both phases in a high-spin state at all pressures and over the entire temperature range investigated, i.e., up to 3000 K. The spin state is conserved after temperature quenching. A formation path is favored where Fe$^{3+}_4$C$_3$O$_{12}$ forms first and then reacts to Fe$^{2+}_2$Fe$^{3+}_2$C$_4$O$_{13}$, most likely accompanied by the formation of oxides. Density functional theory calculations of Fe$^{2+}_2$Fe$^{3+}_2$C$_4$O$_{13}$ at 80 GPa confirm the experimental findings with both ferric and ferrous iron in high-spin state with antiferromagnetic order at 80 GPa. As the intercrystalline cation partitioning between the Fe-bearing carbonates and the surrounding perovskite and ferropericlase depends on the spin state of the iron, an understanding of the redox conditions prevalent in subducted slab regions in the lower mantle has to take the latter into account. Especially, Fe$^{2+}_2$Fe$^{3+}_2$C$_4$O$_{13}$ may play a key role in subducted material in the lower mantle, potentially with a similar role as silicate perovskite., Published by Inst., Woodbury, NY

Review of scientific instruments 93(3), 033904 (2022). doi:10.1063/5.0071786, The success of high-pressure research relies on the inventive design of pressure-generating instruments and materials used for their construction. In this study, the anvils of conical frustum or disk shapes with flat or modified culet profiles (toroidal or beveled) were prepared by milling an Ia-type diamond plate made of a (100)-oriented single crystal using the focused ion beam. Raman spectroscopy and synchrotron x-ray diffraction were applied to evaluate the efficiency of the anvils for pressure multiplication in different modes of operation: as single indenters forced against the primary anvil in diamond anvil cells (DACs) or as pairs of anvils forced together in double-stage DACs (dsDACs). All types of secondary anvils performed well up to about 250 GPa. The pressure multiplication factor of single indenters appeared to be insignificantly dependent on the shape of the anvils and their culets’ profiles. The enhanced pressure multiplication factor found for pairs of toroidally shaped secondary anvils makes this design very promising for ultrahigh-pressure experiments in dsDACs., Published by American Institute of Physics, [S.l.]

In the last few years, the superconducting transition temperature, Tc, of hydrogen-rich compounds has increased dramatically, and is now approaching room temperature. However, the pressures at which these materials are stable exceed one million atmospheres and limit the number of available experimental probes - superconductivity has been primarily identified based on electrical transport measurements. Here, we report definitive evidence of the Meissner effect – a key feature of superconductivity – in H3S and LaH10. Furthermore, we have determined characteristic superconducting parameters: a lower critical field Hc1 of ∼1.9 and ∼1.0 T, and a London penetration depth λL of ∼13 and ∼21 nm in Im-3m-H3S and Fm-3m-LaH10, respectively. These compounds have low values of the Ginzburg-Landau parameter κ ∼7–14 and belong to the group of “moderate” type II superconductors.

We have synthesized the orthocarbonate Sr

Physics and chemistry of minerals 46(8), 783 - 793 (2019). doi:10.1007/s00269-019-01039-9, The compressional behaviour of a natural allanite from Lago della Vecchia (upper Cervo valley, Italy) metagranitoids[$^{A1}$(Ca$_{0.69}$Fe$^{2+}$$_{0.31}$)$_{Σ1.00}^{A2}$(Ca$_{0.46}$Ce$_{0.24}$La$_{0.12}$Sm$_{0.02}$Pr$_{0.05}$Nd$_{0.09}$Th$_{0.02}$)$_{Σ1.00}^{M1}$(Al$_{0.65}$Fe$^{3+}$$_{0.34}$Ti$_{0.02}$)$_{Σ1.01}^{M2}$(Al$_{0.99}$)$^{M3}$(Fe$^{3+}_{0.54}$Fe$^{2+}_{0.36}$Mg$_{0.06}$Ti$^{4+}_{0.02}$Al$_{0.01}$)$_{Σ0.99}$ $^{Si1,Si2,Si3}$(Si$_{2.80}$Al$_{0.20}$)$_{Σ3.00}O_{11}$(OH,O)] has been investigated up to 16 GPa (at 298 K) by means of in situsynchrotron single-crystal X-ray diffraction. Experiments have been conducted under hydrostatic conditions, using a diamondanvil cell and the mix methanol:ethanol:water = 16:3:1 (up to 10 GPa) and neon (up to 16 GPa) as pressure-transmittingmedia. No phase transition has been observed within the pressure-range investigated. Data collected in decompression provethat, at least up to 16 GPa (at 298 K), the deformation mechanisms are fully reversible. A third-order Birch–MurnaghanEquation of State (BM-EoS) was fitted to the P–V data (up to 10 GPa), giving: V$_0$ = 470.2(2) Å$^3$, K$_{P0,T0}$ = 131(4) GPa andK′= 1.9(8). The evolution of the lattice parameters with pressure shows a slight anisotropic compression pattern, with K$_{P0,T0}$(a):K$_{P0,T0}$(b):K$_{P0,T0}$(c) = 1.24:1.52:1. The monoclinic β-angle decreases monotonically with pressure, with: $β_{P}(°)$ = $β_{P0}$ – 0.0902(4)P (R$^2$ = 0.997, with P in GPa). The main deformation mechanisms at the atomic scale are described basedon a series of structure refinements at different pressures. A comparison between the compressional behavior of allanite,epidote and clinozoisite is carried out., Published by Springer, Heidelberg

Earth and planetary science letters 507, 166 - 174 (2019). doi:10.1016/j.epsl.2018.11.038, The pressure-induced amorphization of the two endmembers of the plagioclase ((Na$_{1−x}$Cax)Al$_{1+x}$Si$_{3−x}$O$_8$) solid-solution, anorthite (CaAl$_2$Si$_2$O$_8$) and albite (NaAlSi$_3$O$_8$), has been studied as a function of compression rate by means of time-resolved powder diffraction. Anorthite and albite were compressed in a diamond anvil cell to 80 GPa at multiple rates from 0.05 GPa/s to 80 GPa/s. The amorphization pressure decreases with increasing compression rate. This negative strain rate sensitivity indicates a change in deformation mechanism in the plagioclase solid-solution endmembers from brittle to ductile with increasing compression rate. The presented data support the previously proposed shear deformation mechanism for the amorphization of plagioclase. Furthermore, amorphization progresses over a wide pressure range suggesting heterogeneous amorphization, similar to observations based on recovered material from shock-compression experiments of plagioclase. Our experiments support the contention that amorphization pressures for plagioclase may occur at lower pressures than usually considered., Published by Elsevier, Amsterdam [u.a.]

High pressure angle-dispersive X-ray diffraction investigations have been carried out on α-cristobalite form of Al0.5Ga0.5PO4. Our investigations show that the structural stability of this phase un...

Journal of synchrotron radiation 28(3), 688 - 706 (2021). doi:10.1107/S1600577521002551, The high-precision X-ray diffraction setup for work with diamond anvil cells (DACs) in interaction chamber 2 (IC2) of the High Energy Density instrument of the European X-ray Free-Electron Laser is described. This includes beamline optics, sample positioning and detector systems located in the multipurpose vacuum chamber. Concepts for pump–probe X-ray diffraction experiments in the DAC are described and their implementation demonstrated during the First User Community Assisted Commissioning experiment. X-ray heating and diffraction of Bi under pressure, obtained using 20 fs X-ray pulses at 17.8 keV and 2.2 MHz repetition, is illustrated through splitting of diffraction peaks, and interpreted employing finite element modeling of the sample chamber in the DAC., Published by Wiley-Blackwell, [S.l.]

Water-rich planets are common in our galaxy: Uranus and Neptune in our solar system and some of the sub-Neptunes in extrasolar systems1. These planets may have a thick water-rich layer above the rocky interior. Recent models2-4 have invoked possible existence of heavier elements in the water-rich layer of Uranus based on need for explaining the low luminosity5-6. However, it is not well understood how heavy elements can exist and be stabilized in the low-density layer for a sufficiently long period of time. Here we report the results of laser-heated diamond-anvil cell (LH-DAC) experiments on two rock-forming minerals, olivine ((Mg,Fe)2SiO4) and ferropericlase ((Mg,Fe)O), in a H2O medium at the pressure and temperature conditions expected for the interiors of approximately 1-6 Earth-mass water-rich planets. The X-ray diffraction patterns and the morphology of the recovered samples in electron microscopy indicate a selective leaching of MgO from starting olivine during heating and large solubility of MgO in H2O peaking between 20-40 GPa and above 1500 K. The observed reaction can chemically stabilize heavier elements (such as Mg and O) in water-rich layer, providing a key chemical process for explaining the hypothesized heavier element presence at shallow depths in Uranus and possibly other water-rich planets. In addition, the H2O layer of hot and smaller water-rich planets7 (Earth-size) is more likely to have a wider MgO-rich layer than cold and larger water-rich planets where the depth range of the MgO-rich layer is likely to be narrower, enabling a range of geochemical evolution among water-rich planets.

Extreme pressures and temperatures are known to drastically affect the chemistry of iron oxides, resulting in numerous compounds forming homologous series nFeOmFe2O3 and the appearance of FeO2. Here, based on the results of in situ single-crystal x-ray diffraction, Mössbauer spectroscopy, x-ray absorption spectroscopy, and density-functional theory+dynamical mean-field theory calculations, we demonstrate that iron in high-pressure cubic FeO2 and isostructural FeO2H0.5 is ferric (Fe3+), and oxygen has a formal valence less than 2. Reduction of oxygen valence from 2, common for oxides, down to 1.5 can be explained by a formation of a localized hole at oxygen sites. © 2021 American Physical Society. We acknowledge the Deutsches Elektronen-Synchrotron (DESY, PETRA III), the European Synchrotron Radiation Facility (ESRF), and the Advance Photon Source (APS) for provision of beamtime. N. D. and L. D. thank the Federal Ministry of Education and Research, Germany (BMBF, Grant No. 05K19WC1) and the Deutsche Forschungsgemeinschaft (DFG Projects No. DU 954–11/1, No. DU 393–9/2, and No. DU 393–13/1) for financial support. N. D. and I. A. A. thank the Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linköping University (Faculty Grant SFO-Mat-LiU No. 2009 00971). Electronic structure calculations were supported by the Russian Science Foundation (Project No. 18-12-00492). Theoretical analysis of chemical bonding was supported by the Ministry of Science and Higher Education of the Russian Federation in the framework of Increase Competitiveness Program of NUST “MISIS” (No. K2-2019-001) implemented by a governmental decree, No. 211. Support from the Knut and Alice Wallenberg Foundation (Wallenberg Scholar Grant No. KAW-2018.0194), the Swedish Government Strategic Research Areas and SeRC, and the Swedish Research Council (VR) Grant No. 2019-05600 is gratefully acknowledged.

We have studied the ${\mathrm{H}}_{2}\mathrm{O}$ ice VII--ice X phase transition at room temperature by performing three quasicontinuous synchrotron time-resolved x-ray-diffraction experiments in a dynamic diamond anvil cell, reaching pressures of 180 GPa. The dense pressure coverage of our volume data allows us to directly derive the bulk modulus for ${\mathrm{H}}_{2}\mathrm{O}$ over the entire pressure range. Our data document three major changes in compression behavior in the ranges of 35--40, 50--55, and 90--110 GPa, likely corresponding to the formation of pretransition dynamically disordered ice VII and ice X, and static ice X, respectively. Our results confirm that ice X has a very high bulk modulus.

Construction and building materials 266, 121094 (2021). doi:10.1016/j.conbuildmat.2020.121094, The thermal and compressional behaviors of kurnakovite, a potential B-rich aggregate in neutron radiation-shielding concretes, were studied by in situ single-crystal synchrotron X-ray diffraction (100–393 K, 0–13.36(5) GPa). Above 393 K, the crystal structure collapses in response to dehydration. The bulk thermal expansion coefficient is $α_{V(298K)}$ = 5.18(1)∙10$^{−5}$ K$^{−1}$. Volume compressional trend modelled with a Birch-Murnaghan equation of state yields a bulk modulus of K$_{P0,T0}$ = 35(3) GPa. A phase transition occurs between 9.23(5) and 11.11(5) GPa, leading to a triclinic high-P polymorph (with triple unit-cell volume) and to an increase in coordination of one third of the trigonal-planar boron sites to a tetrahedral geometry., Published by Elsevier Science, Amsterdam [u.a.]

The journal of physical chemistry letters 12(12), 3246 - 3252 (2021). doi:10.1021/acs.jpclett.1c00150, The ultrafast synthesis of ε-Fe$_3$N$_{1+x}$ in a diamond-anvil cell (DAC) from Feand N$_2$ under pressure was observed using serial exposures of an X-ray free electron laser (XFEL). When the sample at 5 GPa was irradiated by a pulse train separated by 443 ns, the estimated sample temperature at the delay time was above 1400 K, confirmed by in situ transformation of $α$- to $γ$-iron. Ultimately, the Fe and N$_2$ reacted uniformly throughout the beam path to form Fe$_3$N$_{1.33}$, as deduced from its established equation of state (EOS). We thus demonstrate that the activation energy provided by intense X-ray exposures in an XFEL can be coupled with the source time structure to enable exploration of the time-dependence of reactions under high-pressure conditions., Published by ACS, Washington, DC