Bi Yan

Static strength of gold compressed up to 127 GPa

Gold powder is compressed non-hydrostatically up to 127 GPa in a diamond anvil cell (DAC), and its angle dispersive X-ray diffraction patterns are recorded. The compressive strength of gold is investigated in a framework of the lattice strain theory by the line shift analysis. The result shows that the compressive strength of gold increases continuously with the pressure up to 106 GPa and reaches 2.8 GPa at the highest experimental pressure (127 GPa) achieved in our study. This result is in good agreement with our previous experimental result in a relevant pressure range. The compressive strength of gold may be the major source of the error in the equation-of-state measurement in various pressure environments.

Ruby fluorescence pressure scale: Revisited

Effect of non-hydrostatic stress on X-ray diffraction in a diamond anvil cell (DAC) is studied. The pressure gradient in the sample chamber leads to the broadening of the diffraction peaks, which increase with the hkl index of the crystal. It is found that the difference between the determined d-spacing compressive ratio d/d0 and the real d-spacing compressive ratio dr/d0 is determined by the yield stress of the pressure transmitting media (if used) and the shear modulus of the sample. On the basis of the corrected experiment data of Mao et al. (MXB86), which was used to calibrate the most widely used ruby fluorescence scale, a new relationship of ruby fluorescence pressure scale is corrected, i.e., P = (1904/9.827)[(1 + Δλ/λ0)9.827−1].

Implementation of LDA+DMFT with the pseudo-potential-plane-wave method

We propose an efficient implementation of combining dynamical mean field theory (DMFT) with electronic structural calculation based on the local density approximation (LDA). The pseudo-potential-plane-wave method is used in the LDA part, which enables it to be applied to large systems. The full loop self consistency of the charge density has been reached in our implementation, which allows us to compute the total energy related properties. The procedure of LDA+DMFT is introduced in detail with a complete flow chart. We have also applied our code to study the electronic structure of several typical strong correlated materials, including cerium, americium and NiO. Our results fit quite well with both the experimental data and previous studies.

Structural and magnetic transition in stainless steel Fe-21Cr-6Ni-9Mn up to 250 GPa

Stainless steel Fe-21Cr-6Ni-9Mn (SS 21-6-9), with similar to 21% Cr, similar to 6% Ni, and similar to 9% Mn in weight percentage, has wide applications in extensive fields. In the present study, SS 21-6-9 is compressed up to 250 GPa, and its crystal structures and compressive behaviors are investigated simultaneously using the synchrotron angle-dispersive x-ray diffraction technique. The SS 21-6-9 undergoes a structural phase transition from fcc to hcp structure at similar to 12.8 GPa with neglectable volume collapse within the determination error under the quasi-hydrostatic environment. The hcp structure remains stable up to the highest pressure of 250 GPa in the present experiments. The antiferromagnetic-to-nonmagnetic state transition of hcp SS 21-6-9 with the changes of inconspicuous density and structure, is discovered at similar to 50 GPa, and revealed by the significant change in c/a ratio. The hcp SS-21-6-9 is compressive anisotropic: it is more compressive in the c-axis direction than in the a-axis direction. Both the equations of states (EOSs) of fcc and hcp SS 21-6-9, which are in accordance with those of fcc and hcp pure irons respectively, are also presented. Furthermore, the c/a ratio of hcp SS 21-6-9 at infinite compression, R infinity, is consistent with the values of pure iron and Fe-10Ni alloy.

Grüneisen Parameter along Hugoniot and Melting Temperature of ε-Iron: a Result from Thermodynamic Calculations

Based on the available data of specific heat Cv at constant volume and the Gruneisen parameter γ of both lattice and electron contributions, we present a consistent method for simultaneously calculating the effective or synthesized Gruneisen parameter along Hugoniot, γeH, covering solid, mixed, and liquid states, and the melting temperature Tm for e-iron. The rationality validation for this method is confirmed as compared with the experimental data, including the measured Tm and Hugoniot bulk sound velocities Cb. The calculated γeH and Tm for e-iron at the Earths inner-core boundary (330 GPa) are 1.58 and 5930 K, respectively, which are close to the values of 1.53 and 6050 K given by Anderson [J. Phys. Chem. Solids 64 (2003) 2125]. This method for determination of γeH could be, in principle, also applicable to any thermodynamic state calculations, e.g., along isothermal and isentropic paths, other than the Hugoniot locus.