Content about Research Highlight

April 3, 2018

Recent discoveries of several stable dense hydrous minerals at high pressure–temperature conditions have led to an important implication of a massive water reservoir in the Earth’s lower mantle. A research team used HPCAT facility and demonstrated that (Fe,Al)OOH can be stabilized in a hexagonal lattice at 107–136 GPa and 2,400 K.  More...

Recent discoveries of several stable dense hydrous minerals at high pressure–temperature conditions have led to an important implication of a massive water reservoir in the Earth’s lower mantle. A research team used HPCAT facility and demonstrated that (Fe,Al)OOH can be stabilized in a hexagonal lattice at 107–136 GPa and 2,400 K. By combining powder X-ray-diffraction techniques with multigrain indexation, the team has determined this hexagonal hydrous phase with a = 10.5803(6) Å and c = 2.5897(3) Å at 110 GPa, which is stable under the deep lower mantle conditions and can transform to the cubic pyrite structure at low T with the same density. The hexagonal phase can be produced when δ-AlOOH in the subducting slabs incorporates FeOOH under the deep lower mantle conditions. Subducting along with the continuous slab penetration, the hexagonal phase might accumulate at the bottom of the lower mantle due to its ultrahigh density.

March 19, 2018

By engineering molecules with mechanically heterogeneous components with a compressible (‘soft’) mechanophore and incompressible (‘hard’) ligands, a research team has created ‘molecular anvils’, resulting in isotropic stress that leads to relative motions of the rigid ligands, anisotropically deforming the compressible mechanophore and activating bonds. More...

By engineering molecules with mechanically heterogeneous components with a compressible (‘soft’) mechanophore and incompressible (‘hard’) ligands, a research team has created ‘molecular anvils’, resulting in isotropic stress that leads to relative motions of the rigid ligands, anisotropically deforming the compressible mechanophore and activating bonds. Conversely, rigid ligands in steric contact impede relative motion, blocking reactivity. X-ray experiments, including the use of x-ray absorption measurements at HPCAT, demonstrate hydrostatic-pressure-driven redox reactions in metal–organic chalcogenides, incorporating molecular elements that have heterogeneous compressibility, in which bending of bond angles or shearing of adjacent chains activates the metal–chalcogen bonds, leading to the formation of the elemental metal.

March 19, 2018

Topological Kondo insulator possesses characteristics of both the strong electron correlations and the topological configurations, as shown in a mixed-valence material SmB6. YbB6 is a structural analog of SmB6, but remains controversial whether compressed YbB6 material is a topological insulator or a Kondo topological insulator. A research team used HPCAT facility and performed x-ray measurements on YbB6 samples. More...

Topological Kondo insulator possesses characteristics of both the strong electron correlations and the topological configurations, as shown in a mixed-valence material SmB6. YbB6 is a structural analog of SmB6, but remains controversial whether compressed YbB6 material is a topological insulator or a Kondo topological insulator. A research team used HPCAT facility and performed x-ray measurements on YbB6 samples. Both the high-pressure powder x-ray diffraction and optical Raman measurements show no trace of structural phase transitions in YbB6 up to 50 GPa. The x-ray absorption measurements reveal a gradual change of Yb valence from nonmagnetic Yb2+ to magnetic Yb3+ above 18 GPa concomitantly with the increase in resistivity.

February 13, 2018

At temperatures (<319 K or <46 oC) where life is sustained, water is an abnormal liquid, having a number of anomalous properties.  It has been widely accepted that water’s anomalies are not a result of simple thermal fluctuation, but are connected to the formation of various structural aggregates in the hydrogen bonding network. To understand water’s anomalous behavior, a two-liquid model with a high-density liquid (HDL) and a low-density liquid (LDL) has been proposed from theoretical simulations. However, it has been experimentally challenging to probe the region of the phase diagram of H2O, often referred to as water’s no man’s land, where the LDL phase is expected to occur. A team at HPCAT overcame the experimental challenge by adopting a new kinetic pathway to access the region of LDL via decompression of a high-pressure crystal.  More...

At temperatures (<319 K or <46 oC) where life is sustained, water is an abnormal liquid, having a number of anomalous properties. For instance, water displays minima of isobaric heat capacity at 308 K and isothermal compressibility at 319 K which are related to entropy and density fluctuations, respectively. It has been widely accepted that water’s anomalies are not a result of simple thermal fluctuation, but are connected to the formation of various structural aggregates in the hydrogen bonding network. To understand water’s anomalous behavior, a two-liquid model with a high-density liquid (HDL) and a low-density liquid (LDL) has been proposed from theoretical simulations. However, it has been experimentally challenging to probe the region of the phase diagram of H2O, often referred to as water’s no man’s land, where the LDL phase is expected to occur.

February 7, 2018

Understanding the behavior of solids under shock compression, including transformations, their pathways, and kinetics, lies at the core of contemporary static and dynamic compression science. A team led by scientists from Sandia National Laboratories is leveraging the capabilities of two sectors of the APS, HPCAT and DCS, for real-time observations of the kinetics of a shock-driven phase transition in a simple ionic solid, CaF2, a model structure in high-pressure physics. More...

Understanding the behavior of solids under shock compression, including transformations, their pathways, and kinetics, lies at the core of contemporary static and dynamic compression science. A team led by scientists from Sandia National Laboratories is leveraging the capabilities of two sectors of the APS, HPCAT and DCS, for real-time observations of the kinetics of a shock-driven phase transition in a simple ionic solid, CaF2, a model structure in high-pressure physics.

February 7, 2018

Knowledge on the structure and properties of silicate magma under extreme pressure plays an important role in understanding the nature and evolution of Earth’s deep interior.  However, such information is scarce owing to experimental challenges.  Using a recently developed double-stage Paris-Edinburgh press, combined with the multi-angle energy dispersive X-ray diffraction, a team has measured structures of MgSiO3 glass up to 111 GPa.  More...

Knowledge on the structure and properties of silicate magma under extreme pressure plays an important role in understanding the nature and evolution of Earth’s deep interior.  However, such information is scarce owing to experimental challenges.  Using a recently developed double-stage Paris-Edinburgh press, combined with the multi-angle energy dispersive X-ray diffraction, a team has measured structures of MgSiO3 glass up to 111 GPa. The results revealed direct experimental evidence of a structural change in this glass at >88 GPa. The structure above 88 GPa is interpreted as having the closest edge-shared SiO6 structural motifs similar to those of the crystalline MgSiO3 postperovskite, with densely packed oxygen atoms. The pressure of the structural change is broadly consistent with or slightly lower than that of the bridgmanite-to-postperovskite transition in crystalline MgSiO3.

January 29, 2018

Single crystal diamond is the hardest known material and widely used in studies on materials under extreme conditions. Nanocrystalline diamond (NCD) possesses hardness comparable to that of single crystal diamond, while also demonstrating increased fracture toughness and yield strength. A research team using the HPCAT facility was able to generate static pressure of 500 GPa (0.5 TPa) on a tungsten sample as measured by synchrotron x-ray diffraction using the grown NCD as second stage micro-anvils.  More...

Single crystal diamond is the hardest known material and widely used in studies on materials under extreme conditions. Nanocrystalline diamond (NCD) possesses hardness comparable to that of single crystal diamond, while also demonstrating increased fracture toughness and yield strength. Thus, NCD’s is a candidate material as second stage anvils to extend the maximum pressure in static high pressure technology. A research team, using Microwave Plasma Chemical Vapor Deposition, has successfully grown NCD on single crystal diamond anvil surface (Figure). The team used HPCAT facility and is able to generate static pressure of 500 GPa (0.5 TPa) on a tungsten sample as measured by synchrotron x-ray diffraction using the grown NCD as second stage micro-anvils.

January 10, 2018

At sufficiently high pressure, hydrogen is believed to become a monatomic metal with exotic electronic properties. Because of the very high pressures required to create such states, hydrogen-rich compounds have been considered alternative materials that could exhibit many of the properties of atomic metallic hydrogen, such as very high-temperature superconductivity, but at accessible pressures. With the help of theoretical predictions, a research team using the HPCAT facility has successfully synthesized superhydrides with La atoms in an fcc lattice at 170 GPa upon heating to about 1000 K. More...

At sufficiently high pressure, hydrogen is believed to become a monatomic metal with exotic electronic properties. Because of the very high pressures required to create such states, hydrogen-rich compounds have been considered alternative materials that could exhibit many of the properties of atomic metallic hydrogen, such as very high-temperature superconductivity, but at accessible pressures. With the help of theoretical predictions, a research team using the HPCAT facility has successfully synthesized superhydrides with La atoms in an fcc lattice at 170 GPa upon heating to about 1000 K. The results match the predicted cubic metallic phase of LaH10 having cages of thirty-two hydrogen atoms surrounding each La atom. Upon decompression, the fcc-based structure undergoes a rhombohedral distortion of the La sublattice.

January 10, 2018

Nanotwinning is known as a highly effective approach for strengthening structural materials and impeding the degradation of mechanical properties. Recently a major breakthrough was realized when nanotwinned cubic-BN (nt-c-BN) and diamond (nt-diamond) were successfully synthesized from onion-like nanoparticle precursors under high pressure conditions. More...

Nanotwinning is known as a highly effective approach for strengthening structural materials and impeding the degradation of mechanical properties. Recently a major breakthrough was realized when nanotwinned cubic-BN (nt-c-BN) and diamond (nt-diamond) were successfully synthesized from onion-like nanoparticle precursors under high pressure conditions. Understanding the microscopic origin of the twin boundaries, and the formation of such from onion-like precursors, are therefore critically important and can provide guidance to the production of nt-diamond at a larger scale. A research team has studied the nucleation mechanism of nt-diamond samples using multiple experimental and theoretical methods, including the synchrotron diffraction at HPCAT. By a direct high-pressure high-temperature synthesis of nanotwinned diamond from onion carbon without high-density defects, the team has obtained nanotwinned diamond possessing an exceptionally high Vickers hardness of 215 GPa at 4.9 N.

December 22, 2017

A research team has recently developed a new capability at HPCAT. The thermoelectric properties of a polycrystalline SnTe have been measured up to 4.5 GPa at 330 K using the developed method. The SnTe shows an enormous enhancement in Seebeck coefficient, greater than 200 % after 3 GPa, which correlates to a known pressure-induced structural phase transition observed by X-ray diffraction measurement. More...

Thermoelectric materials allow the conversion of heat energy into electrical energy. The efficiency is governed by the dimensionless figure of merit (ZT), which is defined as ZT=(α2 σ T/κ), where α, σ, κ are the Seebeck coefficient, electrical conductivity, and thermal conductivity, respectively. A research team has recently developed a new capability at HPCAT. The thermoelectric properties of a polycrystalline SnTe have been measured up to 4.5 GPa at 330 K using the developed method. The SnTe shows an enormous enhancement in Seebeck coefficient, greater than 200 % after 3 GPa, which correlates to a known pressure-induced structural phase transition observed by X-ray diffraction measurement. Electrical resistance and relative changes to the thermal conductivity were also measured, enabling the determination of relative changes in ZT.

December 22, 2017

Rare earth elements are extensively utilized in a variety of applications including strong permanent magnets, lasers, lighting industry, automobiles, nuclear industry, and medicine. With one of the highest intrinsic magnetic moments (10.6 Bohr Magnetron) among the heavy rare earth elements, Dy exhibits a rich magnetic phase diagram under high-pressure and low-temperature conditions. A research team using HPCAT facility found that Dy has near-zero thermal expansion in the magnetically ordered state and normal thermal expansion in the paramagnetic state   More...

December 22, 2017

The lead hybrid perovskite (e.g. MAPbI3, MA=CH3NH3+) solar cell has been under fast development, with the highest certified power conversion efficiency now exceeding 22 %. The type of perovskite has become the first solution-processable photovoltaic material to surpass the efficiency of dominant crystalline silicon panels. The recently discovered Cs2AgBiBr6 double perovskite exhibits attractive optical and electronic features, making it promising for various optoelectronic applications.  More...

The lead hybrid perovskite (e.g. MAPbI3, MA=CH3NH3+) solar cell has been under fast development, with the highest certified power conversion efficiency now exceeding 22 %. The type of perovskite has become the first solution-processable photovoltaic material to surpass the efficiency of dominant crystalline silicon panels. The recently discovered Cs2AgBiBr6 double perovskite exhibits attractive optical and electronic features, making it promising for various optoelectronic applications. However, its practical performance is hampered by the large band gap. A research team, using HPCAT facility, used high-pressure to regulate band gap in Cs2AgBiBr6 is, and observed a remarkable narrowing band gap through high pressure treatments. Moreover, the narrowed band gap is partially retainable after releasing pressure, promoting its optoelectronic applications.

December 5, 2017

The core–mantle boundary (CMB) represents a region with the largest compositional and rheological contrast within the Earth. Seismological studies have revealed a number of thin domains, with variable thicknesses of 5–40 km, lying directly above the CMB, called ULVZs. However, their origin has long been debated. Recently at HPCAT, hydrogen-bearing iron peroxide (FeO2Hx) in the pyrite-type crystal structure was found to be stable under the conditions of the lowermost mantle.  More...

December 5, 2017

In general, few single-crystal organic monomers react under topochemical control to produce single-crystal extended solids. Using a slow compression under uniaxial stress, a team using HPCAT facilities has successfully converted polycrystalline or single-crystal benzene monomer into single-crystalline packings of carbon nanothreads, a one-dimensional sp3 carbon nanomaterial. More...

November 2, 2017

The behavior of the f-electrons in the lanthanides and actinides governs important macroscopic properties but their pressure and temperature dependence is not fully explored. A team from Lawrence Livermore National Laboratory and the Carnegie Institute of Washington has measured the longitudinal (cL) and transverse sound speeds (cT) vs pressure from room temperature to TC for the first time.  More....

The behavior of the f-electrons in the lanthanides and actinides governs important macroscopic properties but their pressure and temperature dependence is not fully explored. For example, the one f-electron in Ce plays an important role in the volume dependence under pressure which contracts abruptly by ~15% at room temperature when the pressure reaches ~0.75 GPa. The crystallographic symmetry remains across the γ-α volume collapse, even though the two fcc phases are quite different. The iso-structural volume collapse from the γ- to the α-phase ends at high temperatures in a critical point (pC, VC, TC), unique among the elements.

October 6, 2017

Lithium–air (Li–O2) batteries may possess energy densities close to that of gasoline. It is commonly known that the Li–O2 battery often forms insoluble discharge products, mainly oxides, which accelerate the degradation of the electrode and electrolyte, thus reducing the cycle stability and efficiency. Investigation of the stability of oxygen-rich lithium oxides would greatly extend our knowledge on improving the capability and lifetime of lithium–air batteries. More...

Lithium–air (Li–O2) batteries may possess energy densities close to that of gasoline. It is commonly known that the Li–O2 battery often forms insoluble discharge products, mainly oxides, which accelerate the degradation of the electrode and electrolyte, thus reducing the cycle stability and efficiency. Lithium superoxide has been considered as an alternative cathode based on reduced graphene oxide. The major problem is that the lithium superoxide is unstable at ambient condition. Investigation of the stability of oxygen-rich lithium oxides would greatly extend our knowledge on improving the capability and lifetime of lithium–air batteries. Based on the theoretical predictions, a research team has used the HPCAT facility in successfully synthesizing several new stable oxygen-rich lithium oxides under high pressure.

September 18, 2017

Magnesium is the lightest structural metal, 35% lighter than aluminum and 78% lighter than steel, thus possessing an exceptional lightweightness (strength-to-weight ratio). However, because of its hexagonal close packed (hcp) structure, the associated slips in hcp-Mg often causes Mg having limited ductility and formability. A research group using the HPCAT facility has synthesized 5 nm/5 nm Mg/Nb nanocomposites that display exceptional strength, ductility, and thermal stability.  More...

Magnesium is the lightest structural metal, with 35% lighter than aluminum and 78% lighter than steel, thus possessing an exceptional lightweightness (strength-to-weight ratio). However, because of its hexagonal close packed (hcp) structure, the associated slips in hcp-Mg often causes Mg having limited ductility and formability. A research group has synthesized 5 nm/5 nm Mg/Nb nanocomposites that display exceptional strength, ductility, and thermal stability. Using the HPCAT facility, the group found that the Mg present in the 5 nm/5 nm Mg/Nb nanocomposite is of entirely body-centered cubic (bcc) structure, without any trace of hcp Mg.  The bcc nano-Mg leads to a 40% higher strength and 125% increase in strain to failure as compared to 50 nm/50 nm Mg/Nb nanocomposites (where Mg has an hcp structure) made by the same method.

August 29, 2017

C, Si and Ge all have sp3-bonded crystalline phases with cubic diamond structure. Both Si and Ge display well-known sp3-bonded tetrahedral amorphous forms which have widespread applications. However, the counterpart in C, an amorphous form of diamond, has been conspicuously missing and remained a puzzle.  More....

C, Si and Ge all have sp3-bonded crystalline phases with cubic diamond structure. Both Si and Ge display well-known sp3-bonded tetrahedral amorphous forms which have widespread applications. However, the counterpart in C, an amorphous form of diamond, has been conspicuously missing and remained a puzzle. By combining high pressure with in situ laser heating at a specific temperature window, a research group using HPCAT facilities successfully turned amorphous carbon to amorphous diamond. The amorphous diamond has a three dimensional sp3-bonded network structure similar to crystalline diamond, with ultrahigh incompressibility (bulk modulus) comparable to diamond, but lacking long-range periodic order. Moreover, this amorphous diamond is found to be recoverable at ambient conditions. More in Zeng et al., Nature Comm. 8, 322, (2017)

July 17, 2017

The interplay of magnetism and superconductivity in iron-based superconductors remains a subject of extensive studies. Recently, pressure induced superconductivity was observed in Fe-ladder compound BaFe2S3, a quasi-one-dimensional prototype of iron-based superconductors. More....

The interplay of magnetism and superconductivity in iron-based superconductors remains a subject of extensive studies. Recently, pressure induced superconductivity was observed in Fe-ladder compound BaFe2S3, a quasi-one-dimensional prototype of iron-based superconductors. However, it is unclear whether the mechanism of superconductivity in BaFe2S3 is similar to two-dimensional iron-based superconductors. By combining the measurements of electric resistance, magnetic susceptibility, and Fe-Kb x-ray emission spectroscopy at HPCAT,  a research team observed superconductivity in a compressed BaFe2Se3 sample, with the results implying a new family of iron-based superconductors for such one dimensional Fe-ladder compounds .

June 26, 2017

Accurate pressure scales remain a challenging subject in compression science.  In order to intercalibrate the equations of state (EOSs) of the three widely used pressure standards, gold, platinum, and MgO, a research group has measured their unit cell volumes using the laser-heated diamond anvil cell up to 140 GPa and 2500 K.   More...

Accurate pressure scales remain a challenging subject in compression science. Intercomparison of the pressure standards provides important information on their accuracies and reconciles discrepancies between experimental results based on different pressure scales. In order to intercalibrate the equations of state (EOSs) of the three widely used pressure standards, gold, platinum, and MgO, a research group has measured their unit cell volumes using the laser-heated diamond anvil cell up to 140 GPa and 2500 K. The simultaneous measurements of Au+MgO and Pt+MgO allow to compare the EOSs of Au, Pt, and MgO directly at high P-T and further refine them for consistency. At 300 K, three standards agree with each other within ±2.5 GPa to 135 GPa in quasi-hydrostatic media. Refined EOSs have been obtained at 300 K, making the measured results consistent with each other within ±1 GPa up to 135 GPa.

June 23, 2017

For decades it has been believed that lithium, the simplest metallic element, has a complicated ground-state crystal structure. Using synchrotron x-ray diffraction at HPCAT and multiscale simulations with density functional theory and molecular dynamics, a research group has shown that the previously accepted martensitic ground state is metastable. More...

For decades it has been believed that lithium, the simplest metallic element, has a complicated ground-state crystal structure. Using synchrotron x-ray diffraction at HPCAT and multiscale simulations with density functional theory and molecular dynamics, a research group has shown that the previously accepted martensitic ground state is metastable. The new ground state is face-centered cubic. The group shows that different isotopes of lithium (6Li and 7Li) display crystal phase transitions at slightly different pressures and temperatures under similar thermal paths, which could be related to large quantum mechanical effects between the isotopes. Lithium is an extremely challenging material for high-pressure studies: It reacts chemically with many materials (e.g., it causes gasket metals and diamonds to become brittle), and diffraction experiments are challenging because of low scattering cross sections.

June 9, 2017

Carbon gives rise to remarkable classes of materials with combined properties, such as low weight, high strength, hardness, elasticity, and tunable electronic properties, because of the flexibility to form sp-, sp2-, and sp3-hybridized bonds. A research team succeeded to recover an ultrastrong carbon after compressing glassy carbon at various pressure and temperature conditions.  More...

Carbon gives rise to remarkable classes of materials with combined properties, such as low weight, high strength, hardness, elasticity, and tunable electronic properties, because of the flexibility to form sp-, sp2-, and sp3-hybridized bonds. A research team succeeded to recover an ultrastrong carbon after compressing glassy carbon at various pressure and temperature conditions.  The newly created glassy carbons are composed of mixed sp2-sp3 hybridized carbons with a low sp3 component, which gives rise to the unique combination of properties.  The compressed glassy carbons have extraordinary compressive strengths and simultaneously exhibit robust elastic recovery in response to local deformations. This type of carbon is an optimal ultralight and ultrastrong material for a wide range of multifunctional applications.   More in Hu et al. (2017), Science Advances, 3: e1603213, DOI: 10.1126/sciadv.1603213.

April 17, 2017

Zirconium has a low neutron cross section and high degree of corrosion resistance. It is widely used in industry and engineering, in particular in the area of refractory applications. Knowledge of elastic and thermal properties of zirconium is important for understanding the behavior and performance of the materials at extreme conditions. By combining X-ray diffraction and X-ray imaging techniques, together with ultrasonic wave velocity measurements, in a Paris-Edinburgh press at HPCAT, a research team has determined multiple elastic and thermal properties including bulk modulus, shear modulus, Poisson’s ratio, and Debye temperature at high pressure and high temperature conditions.    More...

Zirconium has a low neutron cross section and high degree of corrosion resistance. It is widely used in industry and engineering, in particular in the area of refractory applications. Knowledge of elastic and thermal properties of zirconium is important for understanding the behavior and performance of the materials at extreme conditions.

March 14, 2017

It has been predicted that hydrogen-rich material may promote metallization of hydrogen through chemical pressure imposed by the foreign atoms or molecules. A group utilizing HPCAT’s facility studied a hydrogen rich compound, Ar(H2)2, to ultrahigh pressures over three megabars.  More...

It has been predicted that hydrogen-rich material may promote metallization of hydrogen through chemical pressure imposed by the foreign atoms or molecules. A group utilizing HPCAT’s facility studied a hydrogen rich compound, Ar(H2)2, to ultrahigh pressures over three megabars. Ar(H2)2 is a typical van der Waals compound, in which Ar atoms and H2 molecules are ‘glued’ together by the London dispersion forces, leaving the H2 units preserved.