Stroboscopic X-ray imaging of vibrating dislocations excited by 0.58 GHz phonons

We report on direct imaging, by means of stroboscopic x-ray topography, of phonon-induced dislocation vibrations. X-ray images taken from LiNbO3 crystals excited by 0.58 GHz surface acoustic waves, showed individual acoustic wave fronts as well as their distortions when crossing the dislocation line. The observed contrast is well explained by considering the dynamic deformation field of vibrating dislocation. Comparing simulated deformation maps and x-ray images permitted determination of the local velocities of vibrating dislocations and their viscosity coefficients. We found unexpectedly high velocity values (not far from the speed of sound) and extremely low viscosity coefficients, 2-3 orders of magnitude lower than previously measured in ductile materials.