Abstract:In situ high pressure XRD diffraction and Raman spectroscopy have been performed on 12 nm CeO 2 nanoparticles. Surprisingly, under quasihydrostatic condition, 12 nm CeO 2 nanoparticles maintain the fluorite-type structure in the whole pressure range (0-51 GPa) during the experiments, much more stable than the bulk counterpart (P T ～31 GPa). In contrast, they experienced phase transition at pressure as low as 26 GPa under non-hydrostatic condition (adopting CsCl as pressure medium). Additionally, 32-36 nm CeO 2 nanoparticles exhibit an onset pressure of phase transition at 35GPa under quasihydrostatic condition, and this onset pressure is much lower than our result. Further analysis shows both the experimental condition (i.e., quasihydrostatic or non-hydrostatic) and grain size effect have a significant impact on the high pressure behaviors of CeO 2 nanomaterials.

We have performed the first-principles linear response calculations of the lattice dynamics, thermal equation of state and thermodynamical properties of hcp Os metal by using the plane-wave pseudopotential method. The thermodynamical properties are deduced from the calculated Helmholtz free energy by taking into account the electronic contribution and lattice vibrational contribution. The phonon frequencies at Gamma point are consistent with experimental values and the dispersion curves at various pressures have been determined. The calculated volume, bulk modulus and their pressure derivatives as a function of temperature are in excellent agreement with the experimental results. The calculated specific heat indicates that the electronic contribution is important not only at very low temperatures but also at high temperatures due to the electronic thermal excitation. The calculated Debye temperature at a very low temperature is in good agreement with experimental values and drops to a constant until 100 K.

We use first-principles calculation with pseudo-potential and plane wave method to study the bulk meduli, electronic structures and optical properties of copper halides CuX (X = Cl, Br, I). A comparison of the calculation results with the available experimental results show that it is more suitable using the generalized gradient approximation to study these properties than using the local density approximation. The results show that valence bands of CuXX(X = Cl, Br, I) are dominated by the d bands of Cu. Conduction bands are mainly from s bands of Cu and halide atoms, as well as from p bands of halide atoms. The calculated refractive indices of CuX(X = Cl, Br, I) are 1.887, 2.015, and 2.199, respectively. These results are in good agreement with the those calculated from the Gladstone-Dale relationship.

The effect of temperature on motion of misfit dislocation in the γ/γ' interface of a Ni-based superalloy is studied in periodic simulation cells subjected to an applied shear stress. The simulation results show that no matter what temperature is, the motion of misfit dislocation occurs through the nucleation and the propagation of the double kink; at low temperature, the interaction of the misfit dislocation facilitates the motion of the misfit dislocation; on the contrary, at higher temperature, it can obstruct the motion of the misfit dislocation, and improves the mechanical properties of nickel-base superalloys.