J. Z. Hu

Bio: J. Z. Hu is an academic researcher from Carnegie Institution for Science. The author has contributed to research in topics: Bulk modulus & Phase transition. The author has an hindex of 19, co-authored 37 publications receiving 1929 citations. Previous affiliations of J. Z. Hu include Stony Brook University & Argonne National Laboratory.

Hydrogen clusters in clathrate hydrate.

Abstract: High-pressure Raman, infrared, x-ray, and neutron studies show that H2 and H2O mixtures crystallize into the sII clathrate structure with an approximate H2/H2O molar ratio of 1:2. The clathrate cages are multiply occupied, with a cluster of two H2 molecules in the small cage and four in the large cage. Substantial softening and splitting of hydrogen vibrons indicate increased intermolecular interactions. The quenched clathrate is stable up to 145 kelvin at ambient pressure. Retention of hydrogen at such high temperatures could help its condensation in planetary nebulae and may play a key role in the evolution of icy bodies.

High-pressure phase transitions in Zn 1 − x M x Se ( M = Cd , Fe, and Mn)

Abstract: Energy-dispersive x-ray diffraction was employed to study pressure-induced phase transitions in ${\mathrm{Zn}}_{0.84}{\mathrm{Fe}}_{0.16}$Se, ${\mathrm{Zn}}_{0.9}{\mathrm{Cd}}_{0.1}$Se, and ${\mathrm{Zn}}_{0.76}{\mathrm{Mn}}_{0.24}$Se crystals up to 21.0, 23.3, and 24.3 GPa, respectively. Our result shows that the $B3$ to $B1$ structure transitions for these crystals occurred at 11.4$\ifmmode\pm\else\textpm\fi{}$0.5, 9.5$\ifmmode\pm\else\textpm\fi{}$0.3, and 9.6$\ifmmode\pm\else\textpm\fi{}$0.5 GPa, respectively. Compared to the phase-transition pressure ${(P}_{t})$ of ZnSe (14.4 GPa), a reduction of about 3--5 GPa is exhibited in these ternary compounds. This reduction in phase-transition pressure $\ensuremath{\Delta}{P}_{t}$ in the ternary compounds suggests that the fractional volume change, $(\ensuremath{\Delta}{V/V}_{0})$, of the $B3\ensuremath{-}B1$ phase admixture might be the source of this reduction. Our results indicate that ${P}_{t}$ (with respect to the phase transition pressure 14.4 GPa of ZnSe) is related to the fractional volume change $(\ensuremath{\Delta}{V/V}_{0})$ by the expression ${P}_{t}$=[14.4003+0.1568$(\ensuremath{\Delta}{V/V}_{0})$-0.0281$(\ensuremath{\Delta}{V/V}_{0}{)}^{2}$] GPa.

Pressure induced structural transitions in nanometer size particles of PbS

Abstract: At elevated pressure, PbS undergoes a first order phase transition from the NaCl or B1 structure to an orthorhombic structure. The effects of particle sizes in the nanometer range on this transition have been investigated using energy‐dispersive x‐ray diffraction of synchrotron produced wiggler radiation. Relative to the bulk crystals, the onset of transition pressure showed a significant increase with decreasing particle size. The results also show that compressibility increases with decreasing particle size: this increase is continuous through the phase transition.

The effect of particle size on the structural transitions in zinc sulfide

Abstract: Studies of pressure induced phase transformations of ZnS nanoparticles using diamond anvil cells and synchrotron radiation were carried out to 20.0 GPa. Nanoparticles initially in the zinc-blende and wurtzite phases both transformed to the NaCl phase under the application of pressure. The zinc-blende particles, which were of 2.8 nm size, and the wurtzite particles, which were of 25.3 nm size, transformed to the NaCl phase at 19.0 and 15.0 GPa, respectively. Nanoparticles of the wurtzite phase never regained their initial wurtzite structure but returned to the zinc-blende phase upon downloading the pressure. The resultant zinc-blende nanoparticles transformed to the NaCl phase upon the reapplication of a pressure of 15.0 GPa. Nanoparticles initially in the zinc-blende phase returned to their original phase.

Hydrogen storage in metal–organic frameworks

Abstract: New materials capable of storing hydrogen at high gravimetric and volumetric densities are required if hydrogen is to be widely employed as a clean alternative to hydrocarbon fuels in cars and other mobile applications. With exceptionally high surface areas and chemically-tunable structures, microporous metal–organic frameworks have recently emerged as some of the most promising candidate materials. In this critical review we provide an overview of the current status of hydrogen storage within such compounds. Particular emphasis is given to the relationships between structural features and the enthalpy of hydrogen adsorption, spectroscopic methods for probing framework–H2 interactions, and strategies for improving storage capacity (188 references).

Fundamental principles and applications of natural gas hydrates

Abstract: Natural gas hydrates are solid, non-stoichiometric compounds of small gas molecules and water. They form when the constituents come into contact at low temperature and high pressure. The physical properties of these compounds, most notably that they are non-flowing crystalline solids that are denser than typical fluid hydrocarbons and that the gas molecules they contain are effectively compressed, give rise to numerous applications in the broad areas of energy and climate effects. In particular, they have an important bearing on flow assurance and safety issues in oil and gas pipelines, they offer a largely unexploited means of energy recovery and transportation, and they could play a significant role in past and future climate change.

Chemical and Physical Solutions for Hydrogen Storage

Abstract: Hydrogen is a promising energy carrier in future energy systems. However, storage of hydrogen is a substantial challenge, especially for applications in vehicles with fuel cells that use proton-exchange membranes (PEMs). Different methods for hydrogen storage are discussed, including high-pressure and cryogenic-liquid storage, adsorptive storage on high-surface-area adsorbents, chemical storage in metal hydrides and complex hydrides, and storage in boranes. For the latter chemical solutions, reversible options and hydrolytic release of hydrogen with off-board regeneration are both possible. Reforming of liquid hydrogen-containing compounds is also a possible means of hydrogen generation. The advantages and disadvantages of the different systems are compared.

Post-Perovskite Phase Transition in MgSiO3

Abstract: In situ x-ray diffraction measurements of MgSiO3 were performed at high pressure and temperature similar to the conditions at Earth9s core-mantle boundary. Results demonstrate that MgSiO3 perovskite transforms to a new high-pressure form with stacked SiO6-octahedral sheet structure above 125 gigapascals and 2500 kelvin (2700-kilometer depth near the base of the mantle) with an increase in density of 1.0 to 1.2%. The origin of the D″ seismic discontinuity may be attributed to this post-perovskite phase transition. The new phase may have large elastic anisotropy and develop preferred orientation with platy crystal shape in the shear flow that can cause strong seismic anisotropy below the D″ discontinuity.

Self-Assembling Organic Nanotubes

Abstract: Hollow tubular structures of molecular dimensions perform diverse biological functions in nature. Examples include scaffolding and packaging roles played by cytoskeletal microtubules and viral coat proteins, respectively, as well as the chemical transport and screening activities of membrane channels. In the preparation of such tubular assemblies, biological systems make extensive use of self-assembling and self-organizing strategies. Owing to numerous potential applications in areas such as chemistry, biology, and materials science considerable effort has recently been devoted to preparation of artificial nanotubular structures. This article reviews design principles and the preparation of synthetic organic nanotubes, with special emphasis on noncovalent processes such as self-assembly and self-organization.