Articles

February 7, 2018 02:27 PM

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 06:26 PM

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 04:53 PM

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.

January 10, 2018 05:09 PM

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.

December 22, 2017 01:10 PM

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 22, 2017 01:04 PM

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.