We use a flexible potential model to perform large-scale molecular dynamics simulations of Mg 2 SiO 4 melt up to pressures of 24 GPa and at temperatures between 2390 K and 3200 K. We find that thermal pressure and the Grüneisen parameter γ increase linearly with density, independent on temperature. γ increases from 0.5 at ambient pressure to 0.75 at 24 GPa. While Si stays overwhelmingly in tetrahedral coordination, the coordination of Mg increases significantly under compression, from an average 5-fold coordination at room pressure to 7-fold coordination at 24 GPa. Medium range order in Mg 2 SiO 4 as expressed by X-ray and neutron structure factors change considerably with pressure, with features at low wave-vectors q sharpening considerably and shifting to higher q. Diffusivity of the atomic species in Mg 2 SiO 4 decrease uniformly with pressure and are well described by an Arrhenius law. For viscosity η we find good agreement with experiments at room pressure, and predict a rapid increase with pressure.

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We use a flexible potential model to perform large-scale molecular dynamics simulations on self-diffusivity and viscosity of Mg 2 SiO 4 melt up to pressures of 32 GPa and over a temperature range of 2600 to 3200 K. We find that self-diffusivity decreases and viscosity increases uniformly with pressure, the latter from values of 10

We report first-principles phase diagram calculations for the binary systems HfC-TiC, TiC-ZrC, and HfCZrC. Formation energies for superstructures of various bulk compositions were computed with a plane-wave pseudopotential method. They in turn were used as a basis for fitting cluster expansion Hamiltonians, both with and without approximations for excess vibrational free energies. Significant miscibility gaps are predicted for the systems TiC-ZrC and HfC-TiC, with consolute temperatures in excess of 2000 K. The HfC-ZrC system is predicted to be completely miscibile down to 185 K. Reductions in consolute temperature due to excess vibrational free energy are estimated to be ϳ7%, ϳ20%, and ϳ0%, for HfC-TiC, TiC-ZrC, and HfC-ZrC, respectively. Predicted miscibility gaps are symmetric for HfC-ZrC, almost symmetric for HfC-TiC and asymmetric for TiC-ZrC.

Nanoglasses represent a novel structural modification of amorphous materials, exhibiting properties and structural details that are markedly different from those observed in metallic glasses prepared by rapid quenching. In this review, the synthesis method and the techniques used for charactering the structure of nanoglasses are described together with our current understanding of their salient microstructural features. It is believed that the structure of nanoglasses consists of two distinct amorphous regions give rise to mechanical, thermal, and magnetic properties that are significantly different from those observed in rapidly quenched (RQ) metallic glasses. Nanoglasses, therefore, constitute a distinct new class of amorphous materials and thus opening up new opportunities for their potential use in a number of structural and functional applications.

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