344 / 2019-02-27 08:29:43

Simulation on XRD patterns for Dynamic material

XRD; compressed material; new peak

全体主题 > Science and Technology based on XFEL

X-ray diffraction (XRD) is a useful method to diagnose the property of the materials. With the advent of the X-ray Free Electron Laser (XFEL), the photon flux in one plus is achieved to the level for an XRD experiment. This makes the XRD method suitable for dynamic process within piso-second or even femto-second and the XRD image can be obtained before the sample is changed or destroyed by the XFEL source. So XRD method becomes more important for diagnose of condensed material.
The Coherent X-ray Imaging instrument at the Linac Coherent Light Source is used to study condensed matter systems by using XRD method.
For mesoscale sample, the Fresnel number is not far less than one for simple calculation formula of XRD. But if we divided the mesoscale sample into small grids, the above problem can be solved by modifying the momentum transfer as the function related to the central position of the grids.
The process of the compressing the poly-crystal of Fe was simulated by molecular dynamic(MD) code and the density of the sample is increased for the compression of the shock wave. So the lattice constant was decreased and the XRD pattern may change Simultaneously. We used the initial and partly-compressed poly-crystal as the samples for simulating the XRD patterns and we got the XRD pattern invidiously.
Comparing to XRD pattern of the initial sample, a new peak appeared in the XRD radius profile of the partly-compressed sample. The new peak is with a larger scattered angle than the same lattice index of the initial sample. And it indicates that the compressed density is 9.16 g/cm3 within the range of density from the MD result. Besides it, the phenomenon of broadening peak appeared in the partly-compressed XRD pattern for the increased stress, which is similar to the x-ray diffraction pattern of the lattice evolution in laser-shocked polycrystalline Cu at LCLS. Furthermore, The combination of the XRD and MD simulation could have the capability of predicting the new crystal phase and of optimizing the experiment system at XFEL facility.