Structure of Materials An Introduction to Crystallography, Diffraction and Symmetry

In the previous chapters we have learned how X-rays can be used to study the structure of materials, both in terms of the unit cell dimensions and the atom types and positions. In the present chapter we will describe how other types of radiation can be used to obtain the same and, sometimes, additional information. We will begin with neutron diffraction, which has the added benefit of being sensitive to the magnetic structure of a material. Then we cover electron diffraction, which is typically carried out inside a transmission electron microscope. We conclude with a description of the use of synchrotron X-ray sources.

Introductory remarks

Experimental techniques used to study the structure of materials nearly always involve the scattering of electromagnetic radiation or particle waves from atomic configurations. The Bragg equation, along with the concept of the structure factor, forms the basis of a welldeveloped theory that enables us to understand these scattering processes and the structural information that can be derived from them. X-rays are the most commonly used waves for diffraction experiments. Other important and widely used scattering techniques employ the wave-particle duality of electrons and neutrons.

X-ray diffraction experiments are typically the most economical means of determining crystal structures. X-ray diffractometers are commonly found in university, national, and industrial laboratories. Electron diffraction is typically performed using transmission electron microscopes, which are considerably more expensive than typical X-ray diffractometers, but still common in competitive laboratory facilities. Neutron diffraction, on the other hand, is typically performed at national or international reactor facilities. Highenergy, high-flux X-ray scattering experiments are also used to study materials, but they too require advanced and expensive facilities.