The Chemical Imagination at Work inVery Tight Places

Local Lattice Distortions in Mn[N(CN)2]2 under Pressure

We combined synchrotron-based infrared spectroscopy, Raman scattering, and diamond anvil cell techniques with complementary lattice dynamics calculations to reveal local lattice distortions in Mn[N(CN)2]2 under compression. Strikingly, we found a series of transitions involving octahedral counter-rotations, changes in the local Mn environment, and deformations of the superexchange pathway. In addition to reinforcing magnetic property trends, these pressure-induced local lattice distortions may provide an avenue for the development of new functionalities.

Decomposition Products of Phosphine Under Pressure: PH2 Stable and Superconducting?

Evolutionary algorithms (EAs) coupled with density functional theory (DFT) calculations have been used to predict the most stable hydrides of phosphorus (PHn, n = 1-6) at 100, 150, and 200 GPa. At these pressures phosphine is unstable with respect to decomposition into the elemental phases, as well as PH2 and H2. Three metallic PH2 phases were found to be dynamically stable and superconducting between 100 and 200 GPa. One of these contains five formula units in the primitive cell and has C2/m symmetry (5FU-C2/m). It comprises 1D periodic PH3-PH-PH2-PH-PH3 oligomers. Two structurally related phases consisting of phosphorus atoms that are octahedrally coordinated by four phosphorus atoms in the equatorial positions and two hydrogen atoms in the axial positions (I4/mmm and 2FU-C2/m) were the most stable phases between ∼160-200 GPa. Their superconducting critical temperatures (Tc) were computed as 70 and 76 K, respectively, via the Allen-Dynes modified McMillan formula and using a value of 0.1 for the Coulomb pseudopotential, μ*. Our results suggest that the superconductivity recently observed by Drozdov, Eremets, and Troyan when phosphine was subject to pressures of 207 GPa in a diamond anvil cell may result from these, and other, decomposition products of phosphine.

High-pressure stabilization of argon fluorides

On account of the rapid development of noble gas chemistry in the past half-century both xenon and krypton compounds can now be isolated in macroscopic quantities. The same does not hold true for the next lighter group 18 element, argon, which forms only isolated molecules stable solely in low temperature matrices or supersonic jet streams. Here we present theoretical investigations into a new high-pressure reaction pathway, which enables synthesis of argon fluorides in bulk and at room temperature. Our hybrid DFT calculations (employing the HSE06 functional) indicate that above 60 GPa ArF2-containing molecular crystals can be obtained by a reaction between argon and molecular fluorine.

Pressure-Induced Oriented Attachment Growth of Large-Size Crystals for Constructing 3D Ordered Superstructures

Oriented attachment (OA), a nonclassical crystal growth mechanism, provides a powerful bottom-up approach to obtain ordered superstructures, which also demonstrate exciting charge transmission characteristic. However, there is little work observably pronouncing the achievement of 3D OA growth of crystallites with large size (e.g., submicrometer crystals). Here, we report that SnO2 3D ordered superstructures can be synthesized by means of a self-limited assembly assisted by OA in a designed high-pressure solvothermal system. The size of primary building blocks is 200-250 nm, which is significantly larger than that in previous results (normally <10 nm). High pressure plays the key role in the formation of 3D configuration and fusion of adjacent crystals. Furthermore, this high-pressure strategy can be readily expanded to additional materials. We anticipate that the welded structures will constitute an ideal system with relevance to applications in optical responses, lithium ion battery, solar cells, and chemical sensing.

Alkali subhalides: high-pressure stability and interplay between metallic and ionic bonds

The high pressure stability of alkali subhalides is rationalized by means of a thorough chemical bonding analysis.

A New Route for High-Purity Organic Materials: High-Pressure-Ramp-Induced Ultrafast Polymerization of 2-(Hydroxyethyl)Methacrylate

The synthesis of highly biocompatible polymers is important for modern biotechnologies and medicine. Here, we report a unique process based on a two-step high-pressure ramp (HPR) for the ultrafast and efficient bulk polymerization of 2-(hydroxyethyl)methacrylate (HEMA) at room temperature without photo- and thermal activation or addition of initiator. The HEMA monomers are first activated during the compression step but their reactivity is hindered by the dense glass-like environment. The rapid polymerization occurs in only the second step upon decompression to the liquid state. The conversion yield was found to exceed 90% in the recovered samples. The gel permeation chromatography evidences the overriding role of HEMA2(••) biradicals in the polymerization mechanism. The HPR process extends the application field of HP-induced polymerization, beyond the family of crystallized monomers considered up today. It is also an appealing alternative to typical photo- or thermal activation, allowing the efficient synthesis of highly pure organic materials.

Anvil cell gasket design for high pressure nuclear magnetic resonance experiments beyond 30 GPa

Nuclear magnetic resonance (NMR) experiments are reported at up to 30.5 GPa of pressure using radiofrequency (RF) micro-coils with anvil cell designs. These are the highest pressures ever reported with NMR, and are made possible through an improved gasket design based on nano-crystalline powders embedded in epoxy resin. Cubic boron-nitride (c-BN), corundum (α-Al2O3), or diamond based composites have been tested, also in NMR experiments. These composite gaskets lose about 1/2 of their initial height up to 30.5 GPa, allowing for larger sample quantities and preventing damages to the RF micro-coils compared to precipitation hardened CuBe gaskets. It is shown that NMR shift and resolution are less affected by the composite gaskets as compared to the more magnetic CuBe. The sensitivity can be as high as at normal pressure. The new, inexpensive, and simple to engineer gaskets are thus superior for NMR experiments at high pressures.

Superconducting High-Pressure Phases Composed of Hydrogen and Iodine

Evolutionary structure searches predict three new phases of iodine polyhydrides stable under pressure. Insulating P1-H5I, consisting of zigzag chains of (HI)δ+ and H2 δ− molecules, is stable between 30 and 90 GPa. Cmcm-H2I and P6/mmm-H4I are found on the 100, 150, and 200 GPa convex hulls. These two phases are good metals, even at 1 atm, because they consist of monatomic lattices of iodine. At 100 GPa the superconducting transition temperature, Tc, of H2I and H4I is estimated to be 7.8 and 17.5 K, respectively. The increase in Tc relative to elemental iodine results from a larger ωlog from the light mass of hydrogen and an enhanced λ from modes containing H/I and H/H vibrations.

Stable magnesium peroxide at high pressure

Rocky planets are thought to comprise compounds of Mg and O as these are among the most abundant elements, but knowledge of their stable phases may be incomplete. MgO is known to be remarkably stable to very high pressure and chemically inert under reduced condition of the Earth’s lower mantle. However, in exoplanets oxygen may be a more abundant constituent. Here, using synchrotron x-ray diffraction in laser-heated diamond anvil cells, we show that MgO and oxygen react at pressures above 96 GPa and T = 2150 K with the formation of I4/mcm MgO₂. Raman spectroscopy detects the presence of a peroxide ion (O₂²⁻) in the synthesized material as well as in the recovered specimen. Likewise, energy-dispersive x-ray spectroscopy confirms that the recovered sample has higher oxygen content than pure MgO. Our finding suggests that MgO₂ may be present together or instead of MgO in rocky mantles and rocky planetary cores under highly oxidized conditions.

Pressure Processing of Nanocube Assemblies Toward Harvesting of a Metastable PbS Phase

This materials-by-design approach combines nanocrystal assembly with pressure processing to drive the attachment and coalescence of PbS nanocubes along directed crystallographic dimensions to form a large 3D porous architecture. This quenchable and strained mesostructure holds the storage of large internal stress, which stabilizes the high-pressure PbS phase in atmospheric conditions. Nanocube fusion enhances the structural stability; the large surface area maintains the size-dependent properties.

Hydrogen segregation and its roles in structural stability and metallization: silane under pressure

We present results from first-principles calculations on silane (SiH4) under pressure. We find that a three dimensional P-3 structure becomes the most stable phase above 241 GPa. A prominent structural feature, which separates the P-3 structure from previously observed/predicted SiH4 structures, is that a fraction of hydrogen leaves the Si-H bonding environment and forms segregated H2 units. The H2 units are sparsely populated in the system and intercalated with a polymeric Si-H framework. Calculations of enthalpy of formation suggest that the P-3 structure is against the decomposition into Si-H binaries and/or the elemental crystals. Structural stability of the P-3 structure is attributed to the electron-deficient multicenter Si-H-Si interactions when neighboring silicon atoms are linked together through a common hydrogen atom. Within the multicenter bonds, electrons are delocalized and this leads to a metallic state, possibly also a superconducting state, for SiH4. An interesting outcome of the present study is that the enthalpy sum of SiH4 (P-3 structure) and Si (fcc structure) appears to be lower than the enthalpy of disilane (Si2H6) between 200 and 300 GPa (for all previously predicted crystalline forms of Si2H6), which calls for a revisit of the stability of Si2H6 under high pressure.

High-sensitivity NMR beyond 200,000 atmospheres of pressure

Pressure-induced changes in the chemical or electronic structure of solids require pressures well into the Giga-Pascal (GPa) range due to the strong bonding. Anvil cell designs can reach such pressures, but their small and mostly inaccessible sample chamber has severely hampered NMR experiments in the past. With a new cell design that has a radio frequency (RF) micro-coil in the high pressure chamber, NMR experiments beyond 20 Giga-Pascal are reported for the first time. (1)H NMR of water shows sensitivity and resolution obtained with the cells, and (63)Cu NMR on a cuprate superconductor (YBa2Cu3O7-δ) demonstrates that single-crystals can be investigated, as well. (115)In NMR of the ternary chalcogenide AgInTe2 discovers an insulator-metal transition with shift and relaxation measurements. The pressure cells can be mounted easily on standard NMR probes that fit commercial wide-bore magnets with regular cryostats for field- and temperature-dependent measurements ready for many applications in physics and chemistry.

Combined crystal structure prediction and high-pressure crystallization in rational pharmaceutical polymorph screening

Organic molecules, such as pharmaceuticals, agro-chemicals and pigments, frequently form several crystal polymorphs with different physicochemical properties. Finding polymorphs has long been a purely experimental game of trial-and-error. Here we utilize in silico polymorph screening in combination with rationally planned crystallization experiments to study the polymorphism of the pharmaceutical compound Dalcetrapib, with 10 torsional degrees of freedom one of the most flexible molecules ever studied computationally. The experimental crystal polymorphs are found at the bottom of the calculated lattice energy landscape, and two predicted structures are identified as candidates for a missing, thermodynamically more stable polymorph. Pressure-dependent stability calculations suggested high pressure as a means to bring these polymorphs into existence. Subsequently, one of them could indeed be crystallized in the 0.02 to 0.50 GPa pressure range and was found to be metastable at ambient pressure, effectively derisking the appearance of a more stable polymorph during late-stage development of Dalcetrapib.

Crystal polymorphism can lead to substances with vastly differing physicochemical properties, which has serious implications in the pharmaceutical industry. Here, the authors use in silico polymorph screening to accurately predict the resulting structures under set crystallisation environments.

Molecular CsF5 and CsF2+

D5h star-like CsF5 , formally isoelectronic with known XeF5 (-) ion, is computed to be a local minimum on the potential energy surface of CsF5 , surrounded by reasonably large activation energies for its exothermic decomposition to CsF+2 F2 , or to CsF3  (three isomeric forms)+F2 , or for rearrangement to a significantly more stable isomer, a classical Cs(+) complex of F5 (-) . Similarly the CsF2 (+) ion is computed to be metastable in two isomeric forms. In the more symmetrical structures of these molecules there is definite involvement in bonding of the formally core 5p levels of Cs.

The first example of a mixed valence ternary compound of silver with random distribution of Ag(I) and Ag(II) cations

The reaction between colourless AgSbF6 and sky-blue Ag(SbF6)2 (molar ratio 2 : 1) in gaseous HF at 323 K yields green Ag3(SbF6)4, a new mixed-valence ternary fluoride of silver. Unlike in all other Ag(I)/Ag(II) systems known to date, the Ag(+) and Ag(2+) cations are randomly distributed on a single 12b Wyckoff position at the 4̄ axis of the I4̄3d cell. Each silver forms four short (4 × 2.316(7) Å) and four long (4 × 2.764(6) Å) contacts with the neighbouring fluorine atoms. The valence bond sum analysis suggests that such coordination would correspond to a severely overbonded Ag(I) and strongly underbonded Ag(II). Thorough inspection of thermal ellipsoids of the fluorine atoms closest to Ag centres reveals their unusual shape, indicating that silver atoms must in fact have different local coordination spheres; this is not immediately apparent from the crystal structure due to static disorder of fluorine atoms. The Ag K-edge XANES analysis confirmed that the average oxidation state of silver is indeed close to +1⅓. The optical absorption spectra lack features typical of a metal thus pointing out to the semiconducting nature of Ag3(SbF6)4. Ag3(SbF6)4 is magnetically diluted and paramagnetic (μ(eff) = 1.9 μ(B)) down to 20 K with a very weak temperature independent paramagnetism. Below 20 K weak antiferromagnetism is observed (Θ = -4.1 K). Replacement of Ag(I) with potassium gives K(I)2Ag(II)(SbF6)4 which is isostructural to Ag(I)2Ag(II)(SbF6)4. Ag3(SbF6)4 is a genuine mixed-valence Ag(I)/Ag(II) compound, i.e. Robin and Day Class I system (localized valences), despite Ag(I) and Ag(II) adopting the same crystallographic position.

Laser-assisted high-pressure-induced polymerization of 2-(hydroxyethyl)methacrylate

We report on a successful room-temperature polymerization of 2-(hydroxyethyl)methacrylate (HEMA) under high pressure. The polymerization is observed in a limited range of pressures 0.1 to 1.6 GPa without the use of any initiator. When the compressed sample is irradiated at 488 or 355 nm by a laser, the polymerization reaction rate is increased by a factor of 10 or 30, respectively. Moreover, the shift of the laser wavelength to the UV improves the polymerization yield of the recovered sample to 84%. The catalysis of the polymerization process by light results from a one-photon-assisted electron transfer to π* antibonding states of the monomer molecule. The observed polymerization is irreversible and almost complete, which makes this synthesis process suitable for applications.

Pressure-accelerated azide-alkyne cycloaddition: micro capillary versus autoclave reactor performance

Pressure effects on regioselectivity and yield of cycloaddition reactions have been shown to exist. Nevertheless, high pressure synthetic applications with subsequent benefits in the production of natural products are limited by the general availability of the equipment. In addition, the virtues and limitations of microflow equipment under standard conditions are well established. Herein, we apply novel-process-window (NPWs) principles, such as intensification of intrinsic kinetics of a reaction using high temperature, pressure, and concentration, on azide-alkyne cycloaddition towards synthesis of Rufinamide precursor. We applied three main activation methods (i.e., uncatalyzed batch, uncatalyzed flow, and catalyzed flow) on uncatalyzed and catalyzed azide-alkyne cycloaddition. We compare the performance of two reactors, a specialized autoclave batch reactor for high-pressure operation up to 1800 bar and a capillary flow reactor (up to 400 bar). A differentiated and comprehensive picture is given for the two reactors and the three methods of activation. Reaction speedup and consequent increases in space-time yields is achieved, while the process window for favorable operation to selectively produce Rufinamide precursor in good yields is widened. The best conditions thus determined are applied to several azide-alkyne cycloadditions to widen the scope of the presented methodology.

Predicting crystal structures and properties of matter under extreme conditions via quantum mechanics: the pressure is on

The role of quantum mechanical calculations in understanding and predicting the behavior of matter at extreme pressures is discussed in this feature contribution.

Exploring the metallic phase of N2O under high pressure

Using the CALYPSO method, we proposed a new metallic structure of N₂O under high pressure.

On the particular importance of vibrational contributions to the static electrical properties of model linear molecules under spatial confinement

The influence of the spatial confinement on the electronic and vibrational contributions to longitudinal electric-dipole properties of model linear molecules including HCN, HCCH and CO₂ is analyzed.

Synthesis, structures and magnetic properties of the dimorphic Mn2CrSbO6oxide

Mn₂CrSbO₆-perovskite was synthesized at high pressure in order to stabilize the small Mn²⁺cations on the A-perovskite site. Mn₂CrSbO₆-ilmenite polymorph can be prepared, starting from the perovskite, by a “hard-soft” phase transformation increasing the temperature at room pressure.

Structural morphologies of high-pressure polymorphs of strontium hydrides

It is now known that the structure and properties of a material can be significantly altered under extreme compression.

Theoretical predictions of novel potassium chloride phases under pressure

Above 350 GPa KCl assumes an hcp lattice that is reminiscent of the isoelectronic noble gas Ar.

Aromaticity, closed-shell effects, and metallization of hydrogen

CONSPECTUS: Recent theoretical and experimental studies reveal that compressed molecular hydrogen at 200-350 GPa transforms to layered structures consisting of distorted graphene sheets. The discovery of chemical bonding motifs in these phases that are far from close-packed contrasts with the long-held view that hydrogen should form simple, symmetric, ambient alkali-metal-like structures at these pressures. Chemical bonding considerations indicate that the realization of such unexpected structures can be explained by consideration of simple low-dimensional model systems based on H6 rings and graphene-like monolayers. Both molecular quantum chemistry and solid-state physics approaches show that these model systems exhibit a special stability, associated with the completely filled set of bonding orbitals or valence bands. This closed-shell effect persists in the experimentally observed layered structures where it prevents the energy gap from closing, thus delaying the pressure-induced metallization. Metallization occurs upon further compression by destroying the closed shell electronic structure, which is mainly determined by the 1s electrons via lowering of the bonding bands stemming from the unoccupied atomic 2s and 2p orbitals. Because enhanced diamagnetic susceptibility is a fingerprint of aromaticity, magnetic measurements provide a potentially important tool for further characterization of compressed hydrogen. The results indicate that the properties of dense hydrogen are controlled by chemical bonding forces over a much broader range of conditions than previously considered.

High hydrostatic pressure: a probing tool and a necessary parameter in biophysical chemistry

High pressures extending up to several thousands of atmospheres provide extreme conditions for biological organisms to survive. Recent studies are investigating the survival mechanisms and biological function of microorganisms under natural and laboratory conditions extending into the GigaPascal range, with applications to understanding the Earth's deep biosphere and food technology. High pressure has also emerged as a useful tool and physical parameter for probing changes in the structure and functional properties of biologically important macromolecules and polymers encountered in soft matter science. Here we highlight some areas of current interest in high pressure biophysics and physical chemistry that are emerging at the frontier of this cross-disciplinary field.

High-sensitivity nuclear magnetic resonance at Giga-Pascal pressures: a new tool for probing electronic and chemical properties of condensed matter under extreme conditions

Nuclear Magnetic Resonance (NMR) is one of the most important techniques for the study of condensed matter systems, their chemical structure, and their electronic properties. The application of high pressure enables one to synthesize new materials, but the response of known materials to high pressure is a very useful tool for studying their electronic structure and developing theories. For example, high-pressure synthesis might be at the origin of life; and understanding the behavior of small molecules under extreme pressure will tell us more about fundamental processes in our universe. It is no wonder that there has always been great interest in having NMR available at high pressures. Unfortunately, the desired pressures are often well into the Giga-Pascal (GPa) range and require special anvil cell devices where only very small, secluded volumes are available. This has restricted the use of NMR almost entirely in the past, and only recently, a new approach to high-sensitivity GPa NMR, which has a resonating micro-coil inside the sample chamber, was put forward. This approach enables us to achieve high sensitivity with experiments that bring the power of NMR to Giga-Pascal pressure condensed matter research. First applications, the detection of a topological electronic transition in ordinary aluminum metal and the closing of the pseudo-gap in high-temperature superconductivity, show the power of such an approach. Meanwhile, the range of achievable pressures was increased tremendously with a new generation of anvil cells (up to 10.1 GPa), that fit standard-bore NMR magnets. This approach might become a new, important tool for the investigation of many condensed matter systems, in chemistry, geochemistry, and in physics, since we can now watch structural changes with the eyes of a very versatile probe.

Lone-pair interactions and photodissociation of compressed nitrogen trifluoride

High-pressure behavior of nitrogen trifluoride (NF3) was investigated by Raman and IR spectroscopy at pressures up to 55 GPa and room temperature, as well as by periodic calculations up to 100 GPa. Experimentally, we find three solid-solid phase transitions at 9, 18, and 39.5 GPa. Vibrational spectroscopy indicates that in all observed phases NF3 remains in the molecular form, in contrast to the behavior of compressed ammonia. This finding is confirmed by density functional theory calculations, which also indicate that the phase transitions of compressed NF3 are governed by the interplay between lone‑pair interactions and efficient molecule packing. Although nitrogen trifluoride is molecular in the whole pressure range studied, we show that it can be photodissociated by mid-IR laser radiation. This finding paves the way for the use of NF3 as an oxidizing and fluorinating agent in high-pressure reactions.

(N(2))(6)Ne(7): A high pressure van der Waals insertion compound

The binary phase diagram of N(2)-Ne mixtures has been measured at 296 K by visual observation and Raman spectroscopy. The topology of the phase diagram points to the existence of the stoichiometric compound N(2))(6)Ne(7). Its structure has been solved by single-crystal synchrotron x-ray diffraction. The N(2) molecules form a guest lattice that hosts the Ne atoms. This insertion compound can be viewed as a clathrate with the centers of the N(2) molecules forming distorted dodecahedron cages, each enclosing 14 Ne atoms. Remarkably, the N(2))(6)Ne(7) compound is somehow the first clathrate organized by the quadrupolar interaction.

Stress-induced nanoparticle crystallization

We demonstrate for the first time a new mechanical annealing method that can significantly improve the structural quality of self-assembled nanoparticle arrays by eliminating defects at room temperature. Using in situ high-pressure small-angle X-ray scattering, we show that deformation of nanoparticle assembly in the presence of gigapascal level stress rebalances interparticle forces within nanoparticle arrays and transforms the nanoparticle film from an amorphous assembly with defects into a quasi-single crystalline superstructure. Our results show that the existence of the hydrostatic pressure field makes the transformation both thermodynamically and kinetically possible/favorable, thus providing new insight for nanoparticle self-assembly and integration with enhanced mechanical performance.

Moissanite anvil cell design for Giga-Pascal nuclear magnetic resonance

A new design of a non-magnetic high-pressure anvil cell for nuclear magnetic resonance (NMR) experiments at Giga-Pascal pressures is presented, which uses a micro-coil inside the pressurized region for high-sensitivity NMR. The comparably small cell has a length of 22 mm and a diameter of 18 mm, so it can be used with most NMR magnets. The performance of the cell is demonstrated with external-force vs. internal-pressure experiments, and the cell is shown to perform well at pressures up to 23.5 GPa using 800 μm 6H-SiC large cone Boehler-type anvils. (1)H, (23)Na, (27)Al, (69)Ga, and (71)Ga NMR test measurements are presented, which show a resolution of better than 4.5 ppm, and an almost maximum possible signal-to-noise ratio.

Light-induced catalyst and solvent-free high pressure synthesis of high density polyethylene at ambient temperature

The combined effect of high pressure and electronic photo-excitation has been proven to be very efficient in activating extremely selective polymerisations of small unsaturated hydrocarbons in diamond anvil cells (DAC). Here we report an ambient temperature, large volume synthesis of high density polyethylene based only on high pressure (0.4-0.5 GPa) and photo-excitation (~350 nm), without any solvent, catalyst or radical initiator. The reaction conditions are accessible to the current industrial technology and the laboratory scale pilot reactor can be scaled up to much larger dimensions for practical applications. FTIR and Raman spectroscopy, and X-ray diffraction, indicate that the synthesised material is of comparable quality with respect to the outstanding crystalline material obtained in the DAC. The polydispersity index is comparable to that of IV generation Ziegler-Natta catalysts. Moreover the crystalline quality of the synthesised material can be further enhanced by a thermal annealing at 373 K and ambient pressure.

Hydrogen-mediated affinity of ions found in compressed potassium amidoborane, K[NH2BH3]

The paper reports on the experimental and theoretical investigation of bonding properties of potassium amidoborane, (K[NH₂BH₃]), which is one of the most promising compounds for hydrogen storage material among metallated derivatives of ammonia borane (NH₃BH₃).

Cationic radii from structures of extremely compressed solids

The cationic radii of metals are derived from the compressibility of solids assuming that extreme compression of metals leads to direct contacts between cations (= atomic cores). In an extremely compressed binary compound the heteronuclear separations are equal to the sum of the cationic radius of the metal and the covalent radius of the nonmetal.

Bonding pathways of high-pressure chemical transformations

A three-stage bonding pathway towards high-pressure chemical transformations from molecular precursors or intermediate states has been identified by first-principles simulations. With the evolution of principal stress tensor components in the response of chemical bonding to compressive loading, the three stages can be defined as the van der Waals bonding destruction, a bond breaking and forming reaction, and equilibrium of new bonds. The three-stage bonding pathway leads to the establishment of a fundamental principle of chemical bonding under compression. It reveals that during high-pressure chemical transformation, electrons moving away from functional groups follow anti-addition, collision-free paths to form new bonds in counteracting the local stress confinement. In applying this principle, a large number of molecular precursors were identified for high-pressure chemical transformations, resulting in new materials.

Implementation of micro-ball nanodiamond anvils for high-pressure studies above 6 Mbar

Since invention of the diamond anvil cell technique in the late 1950s for studying materials at extreme conditions, the maximum static pressure generated so far at room temperature was reported to be about 400 GPa. Here we show that use of micro-semi-balls made of nanodiamond as second-stage anvils in conventional diamond anvil cells drastically extends the achievable pressure range in static compression experiments to above 600 GPa. Micro-anvils (10–50 μm in diameter) of superhard nanodiamond (with a grain size below ∼50 nm) were synthesized in a large volume press using a newly developed technique. In our pilot experiments on rhenium and gold we have studied the equation of state of rhenium at pressures up to 640 GPa and demonstrated the feasibility and crucial necessity of the in situ ultra high-pressure measurements for accurate determination of material properties at extreme conditions.

The study of materials at high pressure has been limited by the conditions achievable using single-crystal diamond anvils. The use of anvils that incorporate a second stage consisting of two hemispherical nanocrystalline diamond micro-balls, extends the range of static pressures that can be generated in the lab.