Walking home from school at about the age of seven or eight I picked up a pebble and dashed it to the ground. It split into two and I saw that inside was a series of coloured bands. Thus begun my lifelong fascination with the world of crystals, and this led eventually to having the opportunity to work professionally in this field. Many years ago I used to have my occupation ‘crystallographer’ on my passport: this often meant a long and sometimes tedious discussion with airport immigration officials. Eventually I changed it to ‘physicist’ as then I didn’t have to explain myself.
So, what is crystallography? Put simply, it is the study of crystals. Now, let’s be careful here. I am not talking about all those silly websites advertising ways in which crystals act as magical healing agents, with their chakras, auras, and energy levels. No, this is a serious scientific subject, with around 26 or so Nobel prizes to its credit. And yet, despite this, it remains a largely hidden subject, at least in the public mind.
Crystallography as a science has a long and venerable history going back to the 17th century when the sheer beauty of the symmetry of crystals suggested an underlying order of some kind. For the next three centuries, our knowledge of what crystals actually were was based on conjecture and argument, with a few simple experiments thrown in. From their symmetry and shapes it was argued that crystals must consist of ordered arrangements of minute particles: today we know them as atoms and molecules.
But it was the discovery of X-rays in 1895 that changed all that, for a few years later in 1912 in Germany, Max Laue, Walter Friedrich, and Paul Knipping showed that an X-ray beam incident on a crystal was scattered to form a regular pattern of spots on a film (we call this diffraction). Thus it was proved that X-rays consisted of waves and furthermore this gave direct evidence of the underlying order of atoms in the crystal. Hence Nobel Prize number 1 went to Laue in 1914. However, it was William Lawrence Bragg (WLB) who in 1912 at the age of 22 showed how the observed diffraction pattern could be used to determine the positions of atoms in the crystal, thus launching a completely new scientific discipline, X-ray crystallography. Working with his father, William Henry Bragg (WHB), they quickly determined the crystal structures of several materials starting with that of common salt and diamond. Both father and son shared Nobel prize number 2 in 1915. William Henry Bragg and William Lawrence Bragg went on to create world-class research groups working on a huge range of solid materials and incidentally they were active in encouraging women into science.
Since then X-ray crystallography, which today is used throughout the world, has been the method of choice for determining the crystal structures of organic and inorganic solids, pharmaceuticals, biological substances such as proteins and viruses, and indeed all kinds of solid substances. Crick and Watson’s determination of the double helix of DNA is probably the most well-known example of the use of crystallography, incidentally a discovery made in William Lawrence Bragg’s laboratory in Cambridge. Had it not been for X-ray (and later neutron and electron) crystallography we probably would not have today much of an electronics industry, computer technology, new pharmaceuticals, new materials of all sorts, nor the modern field of genetics. The Braggs left a huge legacy which today continues to make astonishing progress.
Featured image credit: Protein Crystals Use in XRay Crystallography by CSIRO. CC BY 3.0 via Wikimedia Commons