The freezing behavior of gold nanoclusters was studied by employing molecular dynamics simulations based on the semiempirical embedded-atom method. Investigations of the gold nanoclusters revealed that, just after freezing, ordered nanosurfaces with a fivefold symmetry were formed with interior atoms remaining in the disordered state. Further lowering of temperatures induced nanocrystallization of the interior atoms that proceeded from the surface towards the core region, finally leading to an icosahedral structure. These dynamic processes explain why the icosahedral cluster structure is dominantly formed in spite of its energetic metastability.
A correlation between grain boundary faceting and abnormal grain growth has been observed in recrystallized polycrystalline Ni at varying annealing temperatures, with or without C added. Carburized Ni specimens deformed to 50 pct show faceted grain boundaries and abnormal grain growth when annealed at temperatures below 0.7 T m , where T m is the melting point of Ni in absolute scale. When annealed at or above 0.7 T m , the grain boundaries are smoothly curved and, therefore, have a rough structure, and normal grain growth is observed. In the specimens annealed in vacuum without carburization, all grain boundaries are faceted at 0.55 T m , and some of them become defaceted at higher temperatures. The specimens annealed in vacuum at temperatures between 0.55 and 0.95 T m show abnormal grain growth. When the grain boundaries have a rough structure and are, therefore, nearly isotropic, normal grain growth is indeed expected, as shown by the simulation and analytical treatment. When all or a fraction of the grain boundaries are faceted, with the facet planes corresponding to the singular cusp directions in the variation of the boundary energy against the inclination angle, abnormal grain growth can occur either because some grain boundary junctions become immobile due to a torque effect, or the growth occurs by a step mechanism.
The phase equilibria of the systems SrO-CuO and SrO-'hBi2O3 were studied by X-ray diffraction analysis of quenched powder samples. The compounds SrCuOz and SrzCu03 melt incongruently at 1085" and 1225"C, respectively. The newly found compound Sr6Biz09 decomposes at 965°C into SrO and Sr3Bi206; Sr3Biz06 melts incongruently into SrO and liquid at 1210°C. SrBi204 undergoes a phase transition at =825"C, and although both are nonstoichiometric, the low-temperature phase is slightly poorer in SrO with 33.5 mol% SrO than the high-temperature phase. [
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