From Ideas to Implementation > 4. Photoconductivity >
Outline the methods used by the Braggs to determine crystal structure
- Atoms in metallic crystals are separated by distances of about 10-10
- Waves of wavelength near this value are required for large angle diffraction to occur.
- X-rays have such wavelengths, and therefore X-ray diffraction studies of metals were the most successful for deciphering the crystal structure of metals.
- X-Ray Crystallography: The study of crystal structures using the diffraction patterns produced by scattered X-rays.
- William Bragg and his son Lawrence Bragg carried out a series of experiments involving X-ray crystallography.
- Their general method involved:
- X-rays were directed at the crystal of a metal salt.
- A photographic plate was placed in the path of the X-rays exiting the crystal.
- The X-rays produced a pattern of bright spots and dark sports on the photographic plate, with the spots occurring in specific directions.
- The calculation of the angles between the bright spots allowed the determination of the internal structure of the crystal.
- The work of the Braggs provided evidence for the periodic atomic structure of crystal that had been postulated for many centuries.
- The technique developed by the Braggs has been extremely important in understanding the crystal structure nature of many solids.