Structural Characterization & Phase Analysis
X-ray diffraction is a core area of expertise at Ames Laboratory which supports rapid discovery of caloric materials.
While some materials achieve top caloric performance when they are single phase, others may need additional phases to become useful. Hence, identifying phases that are present in a given sample and finding out how atoms and molecules are arranged in each of the detected phases are two kinds of very basic, yet critically important, information for the Consortium. Crystallographic data provide key inputs into first-principles theory and modeling and, when combined with physical property and caloric performance data, serve as a basis for identifying structure-property relationships.
When reliably known, the structure-property-performance information is employed by the consortium researchers to make informed decisions about what chemistries and structures are among the most promising for future work and what adjustments will be most beneficial to maximize caloric effect(s), adjust hysteresis and improve mechanical stability of either an individual compound or a whole family of related materials.
Structural characterization and phase analyses are commonly performed at room temperature and pressure, at temperatures that can be adjusted from close to absolute zero to 1000 Kelvin, and in magnetic fields that range from 0 to 4 Tesla. The consortium researchers utilize various powder and single crystal diffractometers. These fully automated devices allow rapid and dependable determination of the atomic and/or molecular structures that includes:
- Coordinates of atoms
- Site occupancies
- Atomic thermal displacements
- Compositions and concentrations of different phases, and
- Average grain size and strain
Vitalij K. Pecharsky and Peter Y. Zavalij, Fundamentals of Powder Diffraction and Structural Characterization of Materials, Second Edition, Springer, 209, 741 p. http://www.springer.com/us/book/9780387095783