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.

Restudy of Grüneisen Parameter of Iron in the Pressure Range of 90-160 Gpa

The Hugoniot equation-of-state(EOS)of porous iron with an average initial density of 6.904g/cm^(3) has been measured in the pressure range from 90 to 160GPa,and a good straight fitting D=2.997+1.603u has accordingly been obtained,where D is the shock wave velocity and u the particle velocity,both in units of km/s.Combining this with the Hugoniot EOS of non-porous iron,the Grüneisen EOS and the Rankine-Hugoniot energy conservation relation,and taking the possible solid-liquid transition correction,we have calculated the Grüneisen parameterγof iron and obtained the resultγ0ρ0=γρ=const,withγ0=1.945 andρ0=7.856g/cm^(3),ρbeing the density.

Structural,electronic,optical,elastic properties and Born effective charges of monoclinic HfO_2 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, Young＇s modulus, Poisson＇s ratio, compressibility, Lam6 constant, sound velocity, Debye temperature, and Born effective charges of monoclinic HfO2 are obtained, which may help to understand monoclinic HfO2 for future work.

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 elasto-plasticity on the zero-amplitude point of the oscillatory damping curve is the same as that of viscosity when η= 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.

Elastic Constants of Na and K from Non-parameter Perturbation Calculation

Combining a linear muffin-tin orbital method, which can be used to calculate the total energy and pressure of solids in a self-consistent manner, with a generalized elastic energy equation, a non-parameter perturbation method has been proposed to compute the elastic constant for cubic metals. The pressure dependence of the shear modulus and bulk modulus forNa and K was calculated. It was found that the computed results agree well with experiments.

Electrical Resistivity of Silane Multiply Shock-Compressed to 106 GPa

Since Wigner et al. proposed that hydrogen would become metallic under sufficient pressure compres- sions in 1935,scientists have paid their attention on making metallic hydrogen at high pressures, and con- siderable progresses were made in theoretical and ex- perimental researches. Nellis et al. observed that the electrical resistivity of fluid hydrogen declined by several orders of magnitude when liquid hydrogen was multiply shocked to 140 GPa, and concluded that fluid hydrogen underwent metallization phase tran- sition from semiconductor to metal in their experi- ments. Although further researches should be carried out to distinguish the highly conductive state and the metallic state of fluid hydrogen, researchers have made great efforts to find new technical approaches to de- crease the threshold pressure for hydrogen metalliza- tion. For this purpose, hydrogen-rich compounds at- tract much attention. Some researchers believed that non-hydrogen elements in those compounds may re- duce, to some extent, the activation energy of met- allization by the effect of chemical pre-compression. Silane, a typical hydrogen-rich compound of group IV hydrides, has been the subject of most of the theoretical and experimental research so far, and it was also expected to be a potential candidate for a high-To superconductor at high pressure research.[61 Compared to hydrocarbons,[71 the chemical bonds in the silane molecule are theoretically more sensitive to pressure and temperature. At sufficiently high pres- sure and temperature, the fluid silane possibly be- comes some metallic alloy consisting of hydrogen and silicon elements. Theoretical calculations showed thatthe metallic transition for the silane system may oc- cur even below 100 GPa, while there are also some other later articles that claimed that silane would re- main an insulator up to around 200 GPa and became metallic and supconducting at 220 GPa with a theo- retical Tc of 16 K. Recently, Eremets et al. have re- ported that silane can transform to metal at 50 GPa, even to superconductor of Tc = 17K at 96GPa and 120GPa. The interesting question is whether tile Inetallization transition could occur under lower pres- sure by inulti-shock compression. Nellis et al. mea- sured the electrical conductivities of hydrocarbons shock-compressed to pressures from 20 GPa to 60 GPa, while for silane, experimental data of electrical resis- tivity under shock compression are scarce. In this Let- ter, the electrical resistivity of silane under nmltiply shock compression is obtained, and the experimental technique and data treatment are briefly described.

The C_ν for calculating the shock temperatures of water below 80 GPa

The shock temperatures of water under 35-50 GPa are firstly measured by the optical pyrometry technique. Cν is a constant below 51 GPa (Cν=7.07R), and increases with the temperature above 51 GPa (Cν=(5.76+3.84×10-4T)R). From our calculation, the dissociation has little effect on Cν. But the electron is essential to the Cν calculation.

The Pressure Dependence of Electrical Resistances for Iron,Nickel and Copper

We measured the pressure dependences of electrical resistances for iron,nickel and copper up to 42 GPa.The results at lower pressure range are in agreement withthose reported in literature.In addition,we observed the discontinuities of iron(32-34GPa)and nickel(28.8 GPa).

Hugoniot equation of state of olivine and its geodynamic implications

Large olivine samples were hot-pressed synthesized for shock wave experiments. The shock wave experiments were carried out at pressure range between 11 and 42 GPa. Shock data on olivine sample yielded a linear relationship between shock wave velocity D and particle velocity u described by D=3.56(?0.13)+2.57(?0.12)u. The shock temperature is determined by an energy relationship which is approximately 790°C at pressure 28 GPa. Due to low temperature and short experimental duration, we suggest that no phase change occurred in our sample below 30 GPa and olivine persisted well beyond its equilibrium boundary in metastable phase. The densities of metastable olivine are in agreement with the results of static compression. At the depth shallower than 410 km, the densities of metastable olivine are higher than those of the PREM model, facilitating cold slab to sink into the mantle transition zone. However, in entire mantle transition zone, the shock densities are lower than those of the PREM model, hampering cold slab to flow across the "660 km" phase boundary.

METHOD FOR MEASURING RESISTANCE OF METALS IN DIAMOND ANVIL CELL AND THE MEASUREMENT OF PIEZORESISTANCE COEFFICIENT OF MANCANIN

With an experimental method developed for measuring the electrical resistance of met-als in diamond anvil cell （DAC）, we measured the pressure dependence of resistance ofmanganin up to 18.5 GPa. The relationship between the resistance of manganin and thepressure is linear below 13 GPa. Another linear relationship is obtained in the range of 13-18.5 GPa. A "turning point" of linear relation is formed at 13 GPa. The piezoresistancecoefficient of manganin measured is 0.024 GPa1 below 13 GPa, which is in good agreementwith those given in literature. A new resistance-pressure relation is obtained in the rangeof 13～18.5 GPa. with the piezoresistance coefficient of 0.020 GPa-1.