Liu Fu-Sheng

Structural, electronic, optical, elastic properties and Born effective charges of monoclinic HfO2 from first-principles calculations

First-principles calculations of structural, electronic, optical, elastic, mechanical properties, and Born effective charges of monoclinic HfO2 are performed with the plane-wave pseudopotential technique based on the density-functional theory. The calculated structural properties are consistent with the previous theoretical and experimental results. The electronic structure reveals that monoclinic HfO2 has an indirect band gap. The analyses of density of states and Mulliken charges show mainly covalent nature in Hf-O bonds. Optical properties, including the dielectric function, refractive index, extinction coefficient, reflectivity, absorption coefficient, loss function, and optical conductivity each as a function of photon energy are calculated and show an optical anisotropy. Moreover, the independent elastic constants, bulk modulus, shear modulus, Youngs modulus, Poissons ratio, compressibility, Lame constant, sound velocity, Debye temperature, and Born effective charges of monoclinic HfO2 are obtained, which may help to understand monoclinic HfO2 for future work.

A Direct Comparison between Static and Dynamic Melting Temperature Determinations below 100 GPa

A preliminary experiment of sound velocity measurements for porous iron with initial average density of 6.275 g/cm3 has been performed at pressures below 100 GPa, in order to clarify a long-standing problem that the static melting temperature Tm, mostly below 100 GPa due to its technical limitations, is notably lower than the extrapolated melting data inferred from the shock wave experiments made above 200 GPa, for the sake of making a direct comparison between the experimental static and dynamic melting temperatures in the same pressure region. With the lately proposed Hugoniot sound velocity data analysis technique [Chin. Phys. Lett. 22 (2005) 863], the results deduced from this Hugoniot sound velocity measurement is Tm = 3200 K at 87 GPa and Tm = 3080 K at 80 GPa, which are in good agreement with the two latest static data of Tm = 3510 K at 105 GPa and Tm = 2750 K at 58 GPa, which utilized modern improved double-side laser heating and in situ accurate x-ray diffraction techniques in experiments. It can be concluded that consensus Tm data would be obtained from static and shock wave experiments in the case that the recently improved techniques are adopted in investigations.

Effective Shear Viscosity of Iron under Shock-Loading Condition

We combine the flyer-impact experiment and improve the finite difference method to solve whether the shear viscosity coefficient of shock iron is more reliable. We find that the numerical simulated profile agrees well with the measured one, from which the determined effective shear viscosity coefficients of shocked iron are 3000 ? 100 Pa?s and 4000 ? 100 Pa?s, respectively, at 103 GPa and 159 GPa. These values are more than 2000 ? 300 Pa?s of Li Y L et al.[Chin. Phys. Lett. 26 (2009) 038301] Our values are more reasonable because they are obtained from a comprehensive simulation for the full-shocked perturbation evolving process.

Shear viscosity of aluminum studied by shock compression considering elasto-plastic effects

The strength always exists before the material melts. In this paper, the viscoelastic-plastic model is applied to improve the finite difference method, and the numerical solutions for the disturbance amplitude damping behavior of the sinusoidal shock front in a flyer-impact experiment are obtained. When the aluminum is shocked to 101 GPa, the effect of elastoplasticity on the zero-amplitude point of the oscillatory damping curve is the same as that of viscosity when ? = 700 Pa?s, and the real shear viscosity coefficient of the shocked aluminum is determined to be about 2800?100 Pa?s. Comparing the experiment data with the numerical results of the viscoelastic-plastic model, we find that the aluminum is close to melting at 101 GPa.

A High-Spectral-Resolution Laser Raman System and Its Application in Shock?Compressed Benzene

Raman measurements play an important role in examining the molecular changes associated with shock-induced structural and chemical changes in condensed materials. We combine a high spectra-resolution Raman system with a two-stage light gas gun to provide better quality data than the transient Raman system used previously. Representative measurements are presented for the shock compression of benzene. The high spectral resolution data have provided an insight into molecular changes that could not be obtained from time-resolved methods.

Equation of state and conductivity of shocked heavy water

Hugoniot equation-of-state, ranging from 10 to 43 GPa, and electrical conductivities, over the range from 18 to 39 GPa, of heavy water (D2O) were measured by using a two-stage light-gas gun. It is found that there exists an abrupt volume contraction at around 20 GPa, similar to behavior of light water (H2O) that occurs at a higher pressure around 25 GPa. Considering the phase transition phenomena mentioned above, together with the electrical conductivity data, the shock-induced changed in liquid D2O and H2O are discussed in detail.Hugoniot equation-of-state, ranging from 10 to 43 GPa, and electrical conductivities, over the range from 18 to 39 GPa, of heavy water (D2O) were measured by using a two-stage light-gas gun. It is found that there exists an abrupt volume contraction at around 20 GPa, similar to behavior of light water (H2O) that occurs at a higher pressure around 25 GPa. Considering the phase transition phenomena mentioned above, together with the electrical conductivity data, the shock-induced changed in liquid D2O and H2O are discussed in detail.

Multi-Shock Compression of Dense Hydrogen?Helium Mixture Beyond 100 GPa

A cryogenic target system for preparing the dense gaseous samples is established on a two-stage light-gas gun and is applied to study the equation of state of hydrogen?helium mixture at higher pressures and at high temperatures by means of the multi-shock technique. The recorded optical radiation signal clearly indicates the beginning moments of the third-, fourth-, sixth-, eighth-, and tenth-shock processes, which are in good agreement with the predictions of the Mansoori?Canfield?Ross variational perturbation theory up to the observed ultimate state of 104?GPa.

A fiber-array probe technique for measuring the viscosity of a substance under shock compression

A fiber-array probe is designed to measure the damping behavior of a small perturbed shock wave in an opaque substance, by which the effective viscosity of substance under the condition of high temperature and high pressure can be constrained according to the flyer-impact technique. It shows that the measurement precision of the shock arrival time by using this technique is within 2 ns. To easily compare with the results given by electrical pin technique, the newly developed method is used to investigate the effective viscosity of aluminum (Al). The shear viscosity coefficient of Al is determined to be 1700 Pas at 71 GPa with a strain rate of 3.6 × 106 s−1, which is in good agreement with the results of other methods. The advantage of the new technique over the electrical pin one is that it is applicable for studying the non-conductive substances.

Many-body contributions to cohesive energy of highly compressed solid 4He

A many-body expansion of cohesive energy of solid 4He is made up to five-body term, and short-range two-, three-, four- and five-body contributions have been computed by using the Hartree-Fock self-consistent-field technique and the same atomic basis set (6311G). At high densities the Hartree-Fock part of two- and four-body contributions are repulsive, whereas the three- and five-body ones are attractive. The four-body term increases as much as 15% repulsion of two-body term, and at the same time the five-body term reduces 4% of two-body repulsion at 2.5 cm3/mol. The four- and five-body terms are found to be important to describe short-range inter-atomic interaction correctly and to compute the cohesive energy accurately in a wide compression range from 2.5 to 7.5 cm3/mol.

Solubility of carbon in high-pressure and high-temperature water

The solubility of carbon in water at the pressure of 7.7 GPa and at temperatures of 1000–2900 K is investigated by means of statistical mechanical theory, and it is found that the excess saturation concentration of carbon in hot water is very sensitive to the temperature. The peak of excess saturation concentration is located at 2450 K, according to calculations using the code CHEQ, where the driving force for graphite-to-diamond transformation reaches the maximum. The conclusions are consistent with those from recent diamond synthesis experiments.