Crystallography

The experimental science of crystallography examines how atoms are arranged in crystalline materials. The study of crystallography is crucial to the disciplines of solid-state physics and materials science (condensed matter physics). The name "crystallography" comes from the Greek words krystallos, which means "clear ice, rock-crystal," and graphene, which means "to write," and which refers to all solids with some degree of transparency. The study of crystals relied on physical measurements of their geometry using a goniometer prior to the invention of X-ray diffraction crystallography (see below). This required determining the crystal's symmetry and measuring the angles of the crystal faces with respect to one another and theoretical reference axes (crystallographic axes). A stereographic net, such as a Wulff net or Lambert net, is used to plot each crystal face's location in 3D space. The net shows the pole to each face. Miller indices are used to identify each location. The final plot enables the crystal's symmetry to be determined. The study of the diffraction patterns of a sample hit by a particular type of beam is now a necessary step in the crystallographic process. The most often employed beams are X-rays, but electron and neutron are also sometimes used. By using words like X-ray crystallography, neutron diffraction, and electron diffraction, crystallographers frequently make clear what kind of beam is being employed.