ISSN:
1551-2916
Source:
Blackwell Publishing Journal Backfiles 1879-2005
Topics:
Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
,
Physics
Notes:
The thermodynamic origin, structure, and stability of the thin amorphous films commonly found in grain boundaries in covalent ceramics are investigated by molecular-dynamics simulation. To focus on the purely thermodynamic aspects, any kinetic effects associated with impurity-controlled interface chemistry are excluded by investigating pure silicon (described by the Stillinger–Weber three-body potential). For this single-component covalent model material, we demonstrate that all high-energy boundaries exhibit a universal amorphous structure, with a width of }0.25 nm, whereas low-energy boundaries are crystalline and much sharper. We also demonstrate that introduction of an amorphous film into a crystalline interface lowers the excess energy to a level similar to the energy of two bulk crystalamorphous interfaces. The competition between a narrow crystalline boundary structure and a wider amorphous boundary structure is shown to be governed by the relative excess energies of the atoms in the grain boundaries and in the bulk amorphous phase. These observations suggest that, in principle, amorphous grain-boundary films do not require impurities for their stabilization and that, as first proposed by Clarke, an equilibrium grain-boundary phase of uniform thickness can be the result of purely thermodynamic rather than kinetic factors.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1111/j.1151-2916.1997.tb02889.x
