Interactive guide to diffraction ..

Interactive Tutorial about Diffraction
Interactive example: Short range order

Diffuse scattering
Thermal I
Thermal II
Occupational I
Occupational II
Longitudinal waves
Transversal waves
Short range order
Stacking faults

Interactive examples
Displacement waves
Short range order
Stacking faults

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Contents

This simulation allows one to create a disordered structure containing vacancies with a given chemical short range order. The meaning of correlation values was discussed in the SRO section of this tutorial. The input parameters are the vacancy concentration and the desired correlation values in different direction. Note that not all combinations of correlation values can actually be realized. Check the output for the final achieved values. The simulated structure is 50x50 unit cells in size. One Monte Carlo (MC) cycle is 2500 iterations, i.e. every site was visited once on average. The more cycles are carried out, the more the correlations can 'spread' through the crystal. Additionally one can choose to calculate the resulting X-ray or neutron scattering.

Here are a few questions to explore:

What correlation parameters would create: (i) a random vacancy distribution, (ii) pair of vacancies along x, (iii) a pattern of vacancies like a "5" on a dice, (iv) clustering of the vacancies.
How does a positive or negative correlation along a particular direction affect the diffraction pattern ?
How does the length scale of the ordering influence the pattern, e.g. comparing pairs of vacancies with longer chains ?
What is the influence of the vacancy ordering on the intensity of the Bragg peaks ?

Once you are done, click here to verify your answers.