Physics – Condensed Matter
Scientific paper
2001-12-17
Journal of Non-Crystalline Solids Volumes 307-310, September 2002, Pages 602-612
Physics
Condensed Matter
8 pages with 3 postscript figures embedded; Proceedings of the 4th International Discussion Meeting on Relaxations in Complex
Scientific paper
10.1016/S0022-3093(02)01511-9
After summarizing the phenomenology of pressure amorphization (PA), we present a theory of PA based on the notion that one or more branches of the phonon spectrum soften and flatten with increasing pressure. The theory expresses the anharmonic dynamics of the flat branches in terms of local modes, represented by lattice Wannier functions, which are in turn used to construct an effective Hamiltonian. When the low-pressure structure becomes metastable with respect to the high-pressure equilibrium phase and the relevant branches are sufficiently flat, transformation into an amorphous phase is shown to be kinetically favored because of the exponentially large number of both amorphous phases and reaction pathways. In effect, the critical-size nucleus for the first-order phase transition is found to be reduced to a single unit cell, or nearly so. Random nucleation into symmetrically equivalent local configurations characteristic of the high-pressure structure is then shown to overwhelm any possible domain growth, and an ``amorphous'' structure results.
Cohen Morrel H.
Íñiguez Jorge
Neaton Jeffrey B.
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