Fu-Qian Jing

First-principles investigations of elastic stability and electronic structure of cubic platinum carbide under pressure

[Sun, Xiao-Wei; Chen, Qi-Feng; Cai, Ling-Cang; Jing, Fu-Qian] China Acad Engn Phys, Natl Key Lab Shock Wave & Detonat Phys, Inst Fluid Phys, Mianyang 621900, Peoples R China. [Sun, Xiao-Wei; Chen, Xiang-Rong; Jing, Fu-Qian] Sichuan Univ, Inst Atom & Mol Phys, Sch Phys Sci & Technol, Chengdu 610065, Peoples R China. [Sun, Xiao-Wei] Lanzhou Jiaotong Univ, Sch Math & Phys, Lanzhou 730070, Peoples R China. [Chen, Xiang-Rong] Chinese Acad Sci, Int Ctr Mat Phys, Shenyang 110016, Peoples R China.;Sun, XW (reprint author), China Acad Engn Phys, Natl Key Lab Shock Wave & Detonat Phys, Inst Fluid Phys, Mianyang 621900, Peoples R China;sunxw_lzjtu@126.com chen_qifeng@iapcm.ac.cn xrchen@126.com

Ab initio calculation of lattice dynamics and thermodynamic properties of beryllium

We investigate the phase transition, elastic constants, phonon dispersion curves, and thermal properties of beryllium (Be) at high pressures and high temperatures using density functional theory. By comparing the Gibbs free energy, in the quasiharmonic approximation (QHA), of hexagonal-closed-packed (hcp) with those of the face-centered cubic (fcc) and body-centered-cubic (bcc) we find that the hcp Be is stable up to 390 GPa, and then transforms to the bcc Be. The calculated phonon dispersion curves are in excellent agreement with experiments. Under compression, the phonon dispersion curves of hcp Be do not show any anomaly or instability. At low pressure the phonon dispersion of bcc Be display imaginary along Gamma-N in the T-1 branches. Within the quasiharmonic approximation, we predict the thermal equation of state and other properties including the thermal expansion coefficient, Hugoniot curves, heat capacity, Gruneisen parameter, and Debye temperature

Melting curves and entropy of fusion of body-centered cubic tungsten under pressure

The melting curves and entropy of fusion of body-centered cubic (bcc) tungsten (W) under pressure are investigated via molecular dynamics (MD) simulations with extended Finnis-Sinclair (EFS) potential. The zero pressure melting point obtained is better than other theoretical results by MD simulations with the embedded-atom-method (EAM), Finnis-Sinclair (FS) and modified EAM potentials, and by ab initio MD simulations. Our radial distribution function and running coordination number analyses indicate that apart from the expected increase in disorder, the main change on going from solid to liquid is thus a slight decrease in coordination number. Our entropy of fusion of W during melting, Delta S, at zero pressure, 7.619 J/mol.K, is in good agreement with the experimental and other theoretical data. We found that, with the increasing pressure, the entropy of fusion Delta S decreases fast first and then oscillates with pressure; when the pressure is higher than 100 GPa, the entropy of fusion Delta S is about 6.575 +/- 0.086 J/mol.K, which shows less pressure effect

The pressure-volume-temperature equation of state of MgO derived from shock Hugoniot data and its application as a pressure scale

The pressure-volume-temperature (P-V-T) equation of state (EOS) of MgO is widely used as a pressure scale in static compression experiments. However, there are remarkable inconsistencies among different previously proposed MgO pressure scales. We calculated the P-V-T EOS of MgO up to 300 GPa and 3000 K based on experimental shock Hugoniot data and a simple thermal pressure model within the Mie-Gruneisen-type analysis framework. All of the parameters used can be measured experimentally with high accuracies. We found that, in overall, the calculated P-V-T EOS of MgO has excellent agreement with the available volume compression data over a wide range of pressure and temperature. A comparison of our results with the previous theoretical investigations has also been performed and confirms that our calculated P-V-T EOS of MgO can be used as a reliable pressure scale for static experiments at high pressures and high temperatures.

Elastic and electronic properties of perovskite type superconductor MgCNi3 under pressure

The elastic, electronic and some thermodynamic properties of the non-oxide perovskite type superconductor MgCNi3 under pressure are investigated by first-principles calculations. With the local density approximation as well as the generalized gradient approximation for exchange and correlation, the ground state properties and equation of state are obtained, which agree well with both theoretical calculations and experiments. By the elastic stability criteria, we predict that MgCNi3 is not stable above 58.4 GPa. Moreover, from the calculated pressure dependence of Debye temperature and electronic properties, the cause of the enhancement of Tc with the increasing pressure is analyzed.

Thermal relaxation phenomena across the metal/window interface and its significance to shock temperature measurements of metals

Difficulties in connection with the radiometry measurement of shock temperatures for metals, due to our insufficient knowledge of the high‐pressure thermophysical properties of materials, are discussed in this paper. The thermal radiation histories from shocked iron film/sapphire interfaces are observed. It is found that after the passage of a shock wave, the thermal relaxation process at the metal/window interface is not always so rapid that the available pyrometric system is unable to respond. Shock temperature measurement experiments show that the spectral radiance history observed at this interface consists of an initial spike followed by a plateau, demonstrating distinctly the temperature relaxation behavior. This fact is contrary to the previous arguments in which the interface temperatures instantly approach their time‐independent equilibrium value. Release temperatures are obtained directly from the observed amplitude of the irradiance spike, these values are comparable to those calculated theoret...

Magnetism and phase transitions of iron under pressure

The spin-polarized generalized gradient approximation within the plane-wave pseudopotential density functional theory is employed to investigate the magnetism and phase transition of iron under pressure. It is found that iron has a ferromagnetic body-centered-cubic (bcc) ground state, while at high pressure (such as at the Earths lower mantle and core pressure), the most stable phase is the nonmagnetic hexagonal-close-packed (hcp) phase. For the face-centered-cubic (fcc) iron, we find that there is an intermediate-spin state (IS) during the transformation from the high-spin state (HS) to the low-spin (LS) state under pressure. The transition pressures of the HS -> IS and the IS -> LS are about 15 GPa and 50 GPa, respectively. The magnetism can affect the properties of iron up to 72.9 GPa. From the enthalpy difference between every two phases, we find the phase transition pressures of FM-bcc -> FM-hcp, FM-bcc -> NM-hcp and NM-bcc -> NM-hcp are 14.4 GPa, 29.5 GPa and 42.7 GPa, respectively.

Simple method for reducing shock-wave equation of state to zero Kelvin isotherm for metals

A thermodynamic formulation is proposed for deducing 0 K isotherm from shock Hugoniot data. In comparison to previous published thermodynamic approaches, the characteristic of this one is not requiring heat capacity as input and the used values of Gruneisen parameter merely confined to around ambient condition. Therefore, it keeps away from the difficulties in determining reliable heat capacity and Gruneisen parameter at high temperatures by experiments and theories. The predicted 0 K isotherms for seven selected metals and their related parameters of initial densities, initial bulk moduli, and their first pressure derivatives are all in well agreement with available experiments and theoretical estimations.

The equation of state, shock-induced molecule dissociation, and transparency loss for multi-compressed dense gaseous H2 + D2 mixtures

The experimental equation of state and temperature data of the dense gaseous H2 + D2 mixtures under multi-shock compression were presented in a pressure range of 2–36 GPa and a temperature range of 2300–5300 K. The strong shock wave was produced using the flyer plate impact by accelerated up to 5.1–6.2 km/s with a two-stage light-gas gun and introduced into the plenum gas sample, which was pre-compressed from environmental pressure to 30–40 MPa. Time-resolved spectral radiation histories were acquired with two sets of multi-wavelength channel pyrometers, which were used to determine the shock velocity and shock temperature in the sample. Shock pressure and particle velocity were obtained by the impedance matching method. The experimental data prove the validity of self-consistent fluid variational theory (SFVT) model in the partial dissociation region. The time-resolved spectral radiation histories along with the SFVT calculation show that the shocked gas samples lose their transparency in visible light wavelength ranges of 400–800 nm at about 12.99 GPa and 4413 K or higher.

Self-consistent fluid variational theory for the equation of state and dissociation of dense hydrogen and nitrogen

The self-consistent fluid variational theory (SFVT) is used to calculate the pressure dissociation of dense hydrogen and nitrogen at high temperatures. The accurate high-pressure and high-temperature effective pair potentials are adopted to describe the intermolecular interactions, which are made to consider molecular dissociation. This paper focuses on a mixture of atoms and molecules and is devoted to the study of the phenomenon of pressure dissociation at finite temperature. The equation of state and dissociation degree are calculated from the free energy functions in the temperature range 4000-15 000 K and density range 0.1-3.2 g cm -3 for dense nitrogen and in the temperature range 2000- 10 000 K and density range 0.02-1.0 g cm -3 for dense hydrogen, which can be compared with other approaches and experiments. The pressure dissociation is found to occur in the higher density range, while temperature dissociation is a more gradual effect.