Solving Structures From Phase Information

Crystal structures are described by phase and magnitude components. The phase indicates the location of matter within the crystal, and the magnitude tells how much matter there is. Usual methods of structure determination are indirect, relying exclusively on magnitude. Structures are deduced by iteratively refining computational models and matching them to experimental observations. Now, Philip N. H. Nakashima, Alexander F. Moodie, and Joanne Etheridge of Monash University, in Melbourne, Australia, report a method that determines structures directly from observations of the phase from electron diffraction patterns (Proc. Natl. Acad. Sci. USA 2013, DOI: 10.1073/pnas.1307323110). They use the phase information to plot the planes where matter is most likely to be in the crystal. Where those planes intersect indicates the locations of atoms. By determining the phases associated with just seven diffraction patterns, they were able to solve the structure of α-Al₂O₃ to within 0.1 Å. So far, the method works only for structures with a center of inversion; the researchers are working to extend it to noncentrosymmetric structures.