What is crystallography and who is a crystallographer?

Phil Coppens

Much of Science is based on precise definitions of concepts. Nevertheless we use the words Crystallographer and Crystallography and assume that we know what they mean. Yet there is a vagueness about the exact meaning of the words. In the old days, Crystallography was the study of crystals and in particular their morphology. The work of Groth stands out as an exemplary tabulation of the knowledge of that time. With the discovery of X-rays, all that changed dramatically. Soon Crystallography became synonymous with the study of crystals by X-ray diffraction, which caught the attention of a remarkable group of scientists, by whom it was developed into the prime technique for the determination of the atomic structure of matter.

But Crystallography is not just one technique. Rather all possible methods should be brought to bear on the study of what crystals are, and indeed, of what substances related to crystals are. This means that, though techniques may change, the field remains defined and active, and always will. Very broadly one may say that Crystallography is concerned with the study of the structure of matter at the atomic level in the condensed state. This definition includes a large range of research presented at the IUCr Congress, but is broader than what is often the scope of National Crystallographic meetings. It includes theoretical calculations of solid state structure, as well as techniques such as scanning tunneling and atomic force microscopy. Unfortunately it leaves out the old classical crystal morphology, so our definition still needs fine tuning.

It is important to keep this definition flexible so it allows for the changing use of scientific methods. Any other course will lead to a narrowing of the field, as new techniques come into being at a remarkably rapid pace.

The common usage of the words Crystallography and Crystallographer varies from country to country. Wherever the field is narrowly associated with crystal-structure determination, large scientific communities will be excluded. Where materials scientists, solid state physicists, structural biochemists, and others have become involved in Crystallographic meetings, the field has flourished. The lesson seems to be that for larger meetings, program organization should be decentralized whenever possible. This can be accomplished by subspecialty groups being actively involved in the organization of the program and the invitation of speakers. Within the IUCr this role is fulfilled by our Commissions. New Commissions have been formed in recent years and further initiatives remain welcome. The Commissions are the core of the Union and determine the scope of its activities. The discussion of who is a Crystallographer is bound to continue. If the definition remains flexible, we will move with scientific developments, and remain the vibrant society we enjoy at this time.