Content about Research Highlight

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.

March 13, 2017

As an archetypal semimetal with complex and anisotropic Fermi surface and unusual electric properties (e.g., high electrical resistance, large magnetoresistance, and giant Hall effect), bismuth (Bi) has played a critical role in metal physics. For over a century, Bi has been known to be diamagnetic. A research team observed unusual ferromagnetism in bulk Bi samples recovered from a molten state at pressures of 1.4–2.5 GPa and temperatures above 1,250 K.  More...

As an archetypal semimetal with complex and anisotropic Fermi surface and unusual electric properties (e.g., high electrical resistance, large magnetoresistance, and giant Hall effect), bismuth (Bi) has played a critical role in metal physics. For over a century, Bi has been known to be diamagnetic. A research team observed unusual ferromagnetism in bulk Bi samples recovered from a molten state at pressures of 1.4–2.5 GPa and temperatures above 1,250 K. Using HPCAT facility, the ferromagnetism is found to be associated with a surprising structural memory effect in the molten state. The ability for solid Bi to remember liquid structure motifs seems to be related to structural similarities between the solid and liquid around 2 GPa, where melting temperature is pressure-independent (i.e., no discontinuity in specific volume or density across the melting line).

March 9, 2017

Meteorites preserve evidence of processes ranging from the formation of the solar system to the origin of life on Earth and the potential for extraterrestrial habitability. One mineral of particular interest in meteorites is the phosphate mineral merrillite, an anhydrous end-member of the merrillite–whitlockite solid solution series, with whitlockite being the hydrogenated end member. Recent experimental observations...  More...

Meteorites preserve evidence of processes ranging from the formation of the solar system to the origin of life on Earth and the potential for extraterrestrial habitability. One mineral of particular interest in meteorites is the phosphate mineral merrillite, an anhydrous end-member of the merrillite–whitlockite solid solution series, with whitlockite being the hydrogenated end member. Recent experimental observations have raised a question as to why merrillite rather than whitlockite forms in a melt with available H2O at the time of phosphate crystallization. One possibility is that shock has devolatilized what was, in part or whole, whitlockite into merrillite. A research group, using synchrotron facilities including HPCAT, inspected the shock-transformation products of Mg-whitlockite. Post-shock samples show that merrillite is produced from whitlockite (Figure) during experimental shock events.

March 2, 2017

High-pressure melting anchors the phase diagram of a material, revealing the effect of pressure on the breakdown of the ordering of atoms in the solid. An important case is molybdenum (Mo), which has long been speculated to undergo an exceptionally steep increase in melting temperature when compressed.  Recent HPCAT experiments found a high-slope melting curve in Mo.  More...

High-pressure melting anchors the phase diagram of a material, revealing the effect of pressure on the breakdown of the ordering of atoms in the solid. An important case is molybdenum (Mo), which has long been speculated to undergo an exceptionally steep increase in melting temperature when compressed. On the other hand, previous experiments lacking reliable melting criteria, showed a nearly constant melting temperature as a function of pressure, a large discrepancy with theoretical expectations. Using microstructure to define a material’s molten history, a group in recent HPCAT experiments found a high-slope melting curve in Mo. Synchrotron X-ray diffraction was used to analyze the crystalline microstructures, generated by heating and subsequently rapidly quenching samples in a laser-heated diamond anvil cell.

February 14, 2017

At ambient condition, the chemistry of water is so stable that it is considered as the unit of hydrogen carrier in the hydrosphere. For a long time, cycling of hydrogen is equivalent to the cycling of water in the Earth’s solid crust and mantle. Geoscientists rarely treat water in its decomposable forms, like hydrogen plus oxygen. Using HPCAT facility, a team discovered hydrogen was freed from hydrous minerals in its elemental form.  More...

At ambient condition, the chemistry of water is so stable that it is considered as the unit of hydrogen carrier in the hydrosphere. For a long time, cycling of hydrogen is equivalent to the cycling of water in the Earth’s solid crust and mantle. Geoscientists rarely treat water in its decomposable forms, like hydrogen plus oxygen. Using HPCAT facility, a team discovered hydrogen was freed from hydrous minerals in its elemental form. Starting from a typical hydrous mineral (goethite) and placing it under lower mantle pressure-temperature conditions, they have observed hydrogen released and the hydrogen loss closely related with the heating temperature and duration. The released hydrogen can directly source the liquid outer core, which is considered to have a substantial amount of hydrogen.

January 23, 2017

A metastable liquid may exist under supercooling, sustaining the liquid below the melting point such as supercooled water and silicon. One important question is whether a crystalline solid may directly melt into a sustainable metastable liquid. A research group utilized HPCAT facility and observed first experimental evidence of creating a metastable liquid directly by a different approach.   More...

A metastable liquid may exist under supercooling, sustaining the liquid below the melting point such as supercooled water and silicon. One important question is whether a crystalline solid may directly melt into a sustainable metastable liquid. A research group utilizing HPCAT's facility observed first experimental evidence of creating a metastable liquid directly by a different approach: melting a high-pressure solid crystal of the metal bismuth via a decompression process below its melting point. When a crystal structure of bismuth is decompressed from 3.2 GPa to 1.2 GPa at 489 K, it melts into a liquid at about 2.3 GPa (middle), and then recrystallizes at 1.2 GPa. The decompression-induced metastable liquid can be maintained for hours in static conditions, and transform to crystalline phases when external perturbations, such as heating and cooling, are applied. It occurs in the pressure–temperature region similar to where the supercooled liquid Bi is observed.

January 18, 2017

Extreme magnetoresistance (XMR) has been recently observed in a growing number of topological semimetals. Recent studies on (W/Mo)Te2 and (Zr/Hf)Te5 suggest that pressure suppresses the XMR and gives rise to superconductivity. To search for a relation between XMR and superconductivity, a research team used HPCAT facility to study the effect of pressure on LaBi.  More....

Extreme magnetoresistance (XMR) has been recently observed in a growing number of topological semimetals. Recent studies on (W/Mo)Te2 and (Zr/Hf)Te5 suggest that pressure suppresses the XMR and gives rise to superconductivity. To search for a relation between XMR and superconductivity, a research team used HPCAT facility to study the effect of pressure on LaBi. A disappearance of XMR, together with an appearance of superconductivity, is observed at a pressure of ~3.5 GPa, showing the pressure effect on XMR and superconductivity in LaBi. Different from other superconducting XMR materials, a pressure region of coexistence between superconductivity and XMR is observed in LaBi. The suppression of XMR in LaBi is accompanied by a sign change in the Hall coefficient RH from negative to positive. The change in the crystal structure is found to be responsible for the change in band structure and creates a region of band inversion in LaBi.

January 4, 2017

Spin cross over may be induced by external stimuli such as light, heat, pressure, and magnetic fields, and provides an electronic origin responsible for corporative structural, electrical, magnetic, and/or optical alterations, with wide applications such as in memory, display, and sensor technologies. Based on recent experiments at HPCAT, together with electronic transport data, a research group observed a pressure-driven spin-cross-overs in the 2D honeycomb antiferromagnetic materials MnPS3 and MnPSe3 at room temperature.  More....

Spin cross over may be induced by external stimuli such as light, heat, pressure, and magnetic fields, and provides an electronic origin responsible for corporative structural, electrical, magnetic, and/or optical alterations, with wide applications such as in memory, display, and sensor technologies. Based on recent experiments at HPCAT, together with electronic transport data, a research group observed a pressure-driven spin-cross-overs in the 2D honeycomb antiferromagnetic materials MnPS3 and MnPSe3 at room temperature. Applying pressure to the confined 2D systems leads to a dramatic magnetic moment collapse of Mn2+ (d5) from S = 5/2 to S = 1/2. Significantly, a number of collective phenomena were observed along with the spin change, including a large lattice collapse (∼20% in volume), and the formation of metallic bonding.

December 5, 2016

Strong parallels exist between the packing of tetrahedra and network topologies found in H2O and SiO2 phases. For examples, tridymite and cristobalite are analogues of ice Ih and Ic, respectively; low-energy hypothetical ice analogues of quartz have been predicted theoretically. By loading binary H2 + H2O samples in diamond anvil cells, a team used HPCAT facility and discovered a unique hydrogen-filled, ice-based chiral structure with oxygen topology very similar to the mineral quartz and other, as-of-yet-hypothetical, three-dimensional nets.  More...

Strong parallels exist between the packing of tetrahedra and network topologies found in H2O and SiO2 phases. For examples, tridymite and cristobalite are analogues of ice Ih and Ic, respectively; low-energy hypothetical ice analogues of quartz have been predicted theoretically. By loading binary H2 + H2O samples in diamond anvil cells, a team used HPCAT facility and discovered a unique hydrogen-filled, ice-based chiral structure with oxygen topology very similar to the mineral quartz and other, as-of-yet-hypothetical, three-dimensional nets. Structural examination by single crystal x-ray diffraction shows that the H-bonded network forms large channels along the crystallographic c-axis, leaving the 6a Wyckoff position available for rotationally disordered H2 molecules, which is fully consistent with the single-site, filled-ice-like structure inferred from Raman measurements.