CONSIDERATIONS ON THE PRECURSOR DECAY ANOMALY IN LITHIUM-FLUORIDE

The purpose of this study is to investigate the cause of the precursor decay anomaly in LiF single crystals, based on the stress-time profiles measured by Asay et al. [J. Appl. Phys. 43, 2132 (1972)] which suggest that the decay is caused by an evolving follower wave overtaking the precursor. It is initially inferred using the profiles that this follower wave consists in turn of a contraction wave C, two degenerate contraction waves I, II, a subrarefaction wave R', and a rarefaction wave Rb, which appear consecutively. An exact equation for the relaxation function, which can be applied to all five followers, is then derived. Next, inequalities for the dislocation density at the front of each follower are derived by incorporating their various properties into the equations; these are then evaluated using the experimental data of Gupta, Duvall, and Fowles [J. Appl. Phys. 46, 532 (1975)]. The validity of the approach is confirmed by showing that their predicted densities satisfy the inequalities, although both the evaluations and the predictions are still too large to be true in the early stage of the decay process. Finally, this anomaly is traced to the common use of an illusive precursor decay curve of unrealistically large slope. © 1995 American Institute of Physics.