New Phase in Fluid Hydrogen at Room Temperature

The presence of phase-transition in hydrogen (H2) at around 560 megapascal (MPa) and room temperature was clarified by Raman and x-ray diffraction studies on both pure H2 and graphite-H2 mixture. H2 is intercalated into the nano-space of graphite, which lowers the transition pressure and temporally expands the size of the honeycomb lattice of graphite under pressure up to 600 MPa. It is supposed that is caused by a gas-liquid phase-transition. According to the peak analysis for Q1(J) mode, the ortho-para conversion of H2 gradually begins to appear after the phase-transition pressure even at room temperature, while peak separation is difficult to achieve under pressure above 1.6 gigapascal (GPa) because of significant overlapping of the peak intensities. Because we have missed the ortho-para conversion which could be observed in only such a small pressure range, the fluid phase at room temperature was full of mystery.

BAND STRUCTURE, METALLIZATION AND STRUCTURAL PHASE TRANSITION OF NABR UNDER HIGHPRESSURE

The metallization and the phase transition of the alkali bromide sodium bromide (NaBr) is investigated through its band structure. The equilibrium lattice constant, bulk modulus, pressure derivative of bulk modulus and the phase transition pressure at which the compound undergo structural phase transition from NaCl (B1) to the CsCl (B2) structure is predicted from the total energy calculations. The ground state properties and band gap values are compared with the experimental and other theoretical results. At normal pressure NaBr is a direct band gap insulator. When the pressure is increased there is enhanced overlapping between the wave functions of the neighboring atoms. As a result the widths of the valence and empty conduction bands increase. These changes lead to the narrowing and indirect closing of band gap in NaBr (metallization). It is also confirmed that the metallization and structural phase transition do not occur simultaneously in ionic compounds.

Judging the phase transition pressure of the unknown parent phase if the resulting state is known

Under the condition that the parent phase is unknown, we have directly judged the phase transition points from the new phase.

Characterization of the micro-contaminants from the inner-body of Kraak porcelain excavated from the “Nan’ao I” shipwreck, the South China Sea

In this paper, optical microscopy, SEM–EDS, Raman and FT-IR analyses were used to investigate different types of corrosion product between layers of glaze and body of Kraak porcelain objects that were excavated from “Nan’ao I” shipwreck, the South China Sea. Several contaminants including NaCl, CaSO4·2H2O, FeOOH and FeS2, were found in many of the pores and cracks of the porcelain objects from Jingdezhen Kiln and Zhangzhou Kiln, even after conservation. While compared with the sample of Jingdezhen Kiln, the contaminants in the sample of Zhangzhou Kilns much more severely. The research pointed out that these contaminants were formed due to the marine environment influence and cross-contamination with other metal relics located in the shipwreck, and more contaminants formed in porous structure, hence reduce the porcelain quality. As regards to conservation, the fragility of ceramic objects from underwater contexts are likely to be caused by various kinds of insoluble ferrous salts and its phase transition pressure. Previous studies on this kind of remains tend to focus on the macro-insoluble salts on the enamel surface. In this paper, preliminary investigations were performed for the first time on different kinds of inner micro-corrosion product in China.

Suitability Evaluation of LaNi5 as Hydrogen-Storage-Alloy Actuator by In-Situ Displacement Measurement during Hydrogen Pressure Change

The swelling ability of LaNi5 for application to hydrogen-storage-alloy (HSA) actuator is discussed through the measurement of the swelling ratio in hydrogen. The HSA actuator is driven by hydrogen pressure change causing the swelling of HSA. LaNi5 is one of the candidate materials for HSA actuators as well as palladium. Some prototypes of HSA actuators using LaNi5 have been fabricated; however, the kinetic swelling ability of LaNi5 itself has been not investigated. In this paper, the authors investigated the static and kinetic swelling ability of LaNi5 powder under hydrogen atmosphere. The results showed that the swelling ratio increased by 0.12 at the phase transition pressure. Response time decreased with an increase in the charged pressure during absorption, while it remained constant during discharge. Reaction kinetics revealed that these swelling behaviors were explained by hydrogen absorption and lattice expansion. The swelling ability of LaNi5 was also compared with that of palladium. The results show that LaNi5 swells 1.8 times more than palladium under 0.5 MPa. LaNi5 is suitable for an actuator driven repeatedly under more than the phase transition pressure. Palladium can be used for one-way-operation actuator even under 0.1 MPa since its response time during the evacuation was much longer than during the pressurization.

Theoretical Analysis of Semiconducting Sm1-xEuxS under Pressure

We have investigated the phase transition pressure and associated volume collapse in Sm1–XEuXS alloy (0≤x≤1) which shows transition from discontinuous to continuous as x is reduced. The calculated results from present approach are in good agreement with experimental data available for the end point members (x=0 and x=1). The results for the alloy counter parts are also in fair agreement with experimental data generated from the vegard’s law. An improved interaction potential model has been developed which includes coulomb, three body interaction, polarizability effect and overlap repulsive interaction operative up to second neighbor ions. It is found that the inclusion of polarizability effect has improved our results.

First-principles calculations for transition phase, mechanical and thermodynamic properties of ZnS under extreme condition

The structural and mechanical properties of ZnS in both B3 and B1 phases have been investigated by the generalized gradient approximation (GGA) within the plane-wave pseudopotential density functional theory (DFT). The obtained lattice parameters and bulk modulus of ZnS for both B3 and B1 structures are well in line with the available theoretical and experimental results. Using the enthalpy–pressure data, we have predicted that the phase transition pressure of ZnS from B3 to B1 is 17.26 GPa, which is in good agreement with previous experimental values. The hydrostatic pressure-dependent elastic properties of the two structures, such as bulk modulus, shear modulus and Young’s modulus, are discussed. Then, the mechanical characteristics of ZnS, including ductile/brittle behavior and elastic anisotropy of the two cubic single-crystal structures, are investigated in details. Furthermore, the thermodynamic properties of ZnS under extreme condition are explored by quasi-harmonic Debye modeling. The calculated results show that the ductility and elastic anisotropy increase with pressure clearly except the ductility of B1. Besides, the temperature and pressure dependencies of the heat capacity and the Debye temperature are obtained and analyzed in the wide ranges.

Structural phase transition and photoluminescence properties of wurtzite CdS:Eu3+ nanoparticles under high pressure

Eu dopant increases the phase transition pressure from wurtzite to rocksalt structure compared with CdS nanoparticles. The PL peaks of the Eu3+ ions can used as pressure probe after the quenching of the PL peaks of rocksalt structure CdS.