How can you determine the structure of crystals?
https://en.wikipedia.org/wiki/Crystal_structure
Thanks
Determining the structure of crystals typically involves the use of X-ray crystallography, a widely used technique. Here's a step-by-step explanation of how it works:
1. Crystal growth: Crystals need to be grown before their structure can be determined. This involves obtaining a pure sample of the material and encouraging its molecules or atoms to arrange themselves in a regular pattern. Different methods can be employed, such as slow evaporation, cooling, or precipitation.
2. Data collection: Once crystals have grown, they are placed in an X-ray beam, typically generated by an X-ray diffractometer. The X-rays interact with the electrons in the crystal lattice, resulting in a pattern of diffracted X-rays. These diffracted X-rays contain information about the arrangement of atoms within the crystal structure.
3. Analysis: The diffracted X-rays are recorded on a detector, such as a photographic film or a digital detector, producing a diffraction pattern. This pattern consists of a series of spots or peaks, which represent the interference of X-rays scattered by the crystal lattice.
4. Data interpretation: From the diffraction pattern, a scientist uses mathematical techniques to extract information about the crystal structure. This involves determining the intensity and position of the peaks, as well as their relative strengths.
5. Phase determination: The phase problem is a fundamental challenge in crystallography, as the diffraction pattern alone does not provide the phases (the starting points) needed to calculate the crystal structure. Techniques such as multiple isomorphous replacement, anomalous scattering, or other methodologies are used to overcome this problem and obtain the phases.
6. Model building and refinement: Using the collected data and derived phases, an initial model of the crystal structure is built. This involves assigning atoms to the diffraction peaks based on their positions and intensities. The model is then refined by minimizing the discrepancy between the calculated diffraction pattern generated by the model and the experimental data. Iterative steps of model building and refinement are performed until the best-fit structure is obtained.
7. Validation: Once the crystal structure is determined, it is crucial to validate its correctness. This involves assessing the quality of the experimental data, performing various statistical analyses, and comparing the model with known physical and chemical properties of the crystal.
By following these steps, scientists can determine the detailed atomic arrangement within crystals, providing valuable insights into their properties and potential applications.