Srilankite has an orthorhombic unit cell with sides a=4.70, b=5.55, and c=5.02 Angstroms. The question: Can compositional ordering on the 4 Zr/Ti sites in each cell, across multiple cells, explain the diffraction and HREM images below? Shutting off the O atoms and bonds, as well as perspective, in the model from the right-click menu might help sort this out. We can add javascript buttons to do this sort of thing more directly later.
For example, the bright lattice spacings in the diffraction pattern below may index as multiples of (002) in the direction of the streaks, and as multiples of (220) perpendicular to the streaks (thus parallel to the wire axis). The superlattice (weaker) spots in that case may require Zr substitution periodicities something like two unit cells in length (4 native periodicity units) in each of those directions. Propose a substitution rule that might give rise to this pattern, and we'll simulate some HREM images for more detailed comparison with intensities in experimental images like that below.
Above find a diffraction pattern, and below
a HREM image, of the same nanowire (A).
These independently
contain evidence of an interesting set of
projected periodicities.
To get a start on this answer, you might ask yourself if all Zr/Ti sites are equivalent. Also, what do we know about propensities that Zr atoms might have for either avoiding one another, or for getting together? Here's an early attempt at indexing the pattern above.
Below are a series of diffraction patterns from a different fiber (B), taken at tilts roughly around the fiber axis of +14, +5 and -14 degrees for rgb, respectively.
Below is an overlay of diffraction patterns from fibers A and B to [201] and [101] zones generated by the diffraction exploerer.
Below a HREM image from fiber B might be explained as compositional zoning down [101], as shown?
