ABSTRACT
Crystallographers determine the atomic-level structure of materials. Regardless of the state of the sample, the basic theory of elastic scattering required to determine the atomic arrangement in materials is the same. Particulars of the experiment that allows us to collect reliable data appropriate for structure determination for crystalline, nano-crystalline, liquid, glassy materials etc, will be different. The compromises that accompany collection and interpretation of data when the sample is contained in a high-pressure vessel will be different from those required when the sample to collected at ambient conditions. The basic theory is the same however: diffraction or elastic scattering arises from the interference of radiation scattered from atoms, arranged periodically or not. The x-ray and neutron interference patterns contain amplitude information but not phase. Crystallographers use these patterns and employing chemical intuition, comparisons with related compounds in databases, or more commonly well-known computational techniques, deduce the arrangement of atoms and refine those locations using least squares techniques to a resolution of better than 0.01A˚. A century of work by crystallographers has produced a library of structures that are used by condensed matter scientists to interpret structure-property relationship in materials as diverse as minerals, catalysts and biologically active molecules. More than 18 Nobel prizes emphasize the central role crystallography plays in a variety of research endeavors.
