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A D V A N C E D M A T E R I A L S & P R O C E S S E S | J A N U A R Y 2 0 2 0 3 4 x-ray radiation with the same frequency. Thus, the electron is the basic unit scattering x-ray waves. EXPERIMENTAL PROCEDURE Each structural de- termination usually starts with a single crystal se- lection. A suitable crystal is generally characterized by well-formed faces and uniform optical proper- ties when observed under a polarizing microscope. In practice, crystals are often grown under less than ideal conditions and shape, providing only few recognizable faces due to twinning, intergrowth, or other types of defects. Additionally, not all crys- tals can be examined us- ing the transmitted light due to the opacity of the samples (ore minerals or metal phases). Therefore, Fig. 3 — Diffraction patterns obtained from (a) single-crystal and (b) polycrystalline samples and recorded using a charge- coupled device detector. (a) (b) the most reliable test for any single crystal is to check its diffraction pat- tern (Fig. 3). Observed diffraction spots should be discrete and more or less rounded, and their indexes should be in good agreement with the known unit cell parameters. After a suitable crystal has been se- lected under the microscope, it should be mounted on top of the glass fiber or special nylon loop. A crystal can be fixed by any type of glue (e.g., cyanoacrylate, epoxy resin) that will not react with the crystal. If the sample will be cooled, it is possible to use inert viscous liquids (e.g., motor or Vaseline oil), which will not crystallize at low temperatures. The crystalline sample should next be placed for data collection into a sin- gle-crystal x-ray diffractometer. The scheme can be represented as follows: source of x-rays → goniometer (respon- sible for crystal rotation) → detector of scattered x-rays. ~AM&P For more information: Vladislav Gur- zhiy, associate professor, St. Petersburg State University, University Embank- ment, 7/9, St Petersburg, Russia, 199034, vladislav.gurzhiy@spbu.ru . THE LATEST IN MATERIALS CHARACTERIZATION This article is adapted from “Single-Crystal X-Ray Diffraction,” part of the updated and revised edition of ASM Handbook, Volume 10: Materials Characteri- zation, which is now available in the ASM Digital Library and in print. New to this edition are tables and charts that list the most common characterization methods for different classes of materials. The tables give information on whether the tech- nique is suitable for elemental analysis, qualitative analysis, surface analysis, or alloy verification, and serve as a jumping off point to the more specific technique articles. Visit asminternational.org/hbvol10.