Real-time x-ray diffraction to examine lattice deformation in shocked lithium fluoride crystals.

摘要

Experimental methods to incorporate real-time, x-ray diffraction measurements in plate impact experiments were developed and used to examine lattice deformation in shock compressed LiF crystals. Using three types of diffraction measurements, data were obtained from crystals subjected to uniaxial strain compression along [111] and [100] to examine elastic and elastic-plastic deformation, respectively.;In single diffraction experiments, changes in interplanar spacing in the shock propagation direction were measured to determine longitudinal lattice deformation. Comparing the diffraction results to the macroscopic volume compression revealed that elastic deformation ([111] experiments) resulted in uniaxial compression of the unit cell. In contrast, elastic-plastic deformation ([100] experiments) produced isotropic compression of the unit cell. In multiple diffraction experiments, diffraction data were obtained simultaneously from two sets of lattice planes. Changes in the diffraction peak positions were related to the longitudinal and the transverse lattice deformation; the complexity of the multiple diffraction geometry required the development of an analytic model to design the experiments and to analyze the diffraction data. Multiple diffraction results permit a direct determination of the unit cell compression, and provided a comprehensive verification of the single diffraction results.;Time-resolved, x-ray diffraction measurements, with 2--4 ns resolution, were performed on crystals shocked along [111] to examine the temporal evolution of the diffraction data under shock wave and ramp wave loading. Because of the penetration depth of x-rays, measured in this study, an analytic model was required to interpret the time-resolved data by simulating the diffraction results. Good agreement between the simulations and experimental data was found for both loading conditions, suggesting that the analytic model has broad applicability.