Reply to comments on “Self-diffusion and elastic constants in the anomalous b.c.c. metals”

✍ Scribed by H.I. Aaronson; P.G. Shewmon

• Publisher: Elsevier Science
• Year: 1967
• Weight: 278 KB
• Volume: 15
• Category: Article
• ISSN: 0001-6160
• DOI: 10.1016/0001-6160(67)90144-7

✦ Synopsis

Now wvaph = -Pwv2h so that (aAG/ap)T = AV and any pressure-variation of AF (through elastic moduli) is irrelevant.

A lattice diffusivity increasing with increasing pressure implies a negative activation volume AV.

However, it is not certain that the simple effect on lattice diffusion was measured in the uranium esperiments which employed polycrystalline samples. Parallel experiments with polycrystalline silver produced the same "spurious" result. In both cases diffusivity decreased with increasing pressure at very high pressures.(lO) Since the latter behaviour is known to be characteristic of single crystal silver and its basic diffusion mechanism, this is likely to be true for uranium also.

It is concluded that associating a large part of the diffusion energy in anomalous b.c.c. metals with (Cl1 -C&2 may account for negative activation entropies and (at least in part) for low activation energies. The model does not necessarily imply a temperaturedependent activation energy for vacancy diffusion and it does not account for the (spurious?) initial increase of diffusivity in polycrystalline y-uranium under pressure.

This paper is published by permission of the Central Electricity Generating Board.