ALGORITHM FOR SORTING DIFFRACTION DATA FROM A SAMPLE CONSISTING OF SEVERAL CRYSTALS ENCLOSED IN A SAMPLE ENVIRONMENT APPARATUS

A sample environment apparatus, such as a diamond-anvil cell (DAC), cr yostat or furnace, presents a unique problem for the crystallographer because some of the diffraction data are shadowed by its components. T he first algorithm for sorting diffraction data from a sample consisti ng of several crystals enclosed in a sample environment apparatus is d escribed. This algorithm requires no previous knowledge of the crystal structure of the sample, so it can be used to solve the structures of substances when the growth of one unstrained crystal is unsuccessful. An example is given to illustrate the development and the implementat ion of this algorithm: the identification of the unit cell of a high-p ressure phase of oxygen known as epsilon-oxygen (epsilon-O2). The epsi lon-O2 sample contains at least seven individual crystals and is enclo sed in a DAC. The epsilon-O2 unit cell is monoclinic, it contains eigh t molecules per unit cell and the lattice constants at 19.7 GPa and ro om temperature are a = 3.642, b = 5.491, c = 7.705 angstrom and beta = 116.2-degrees. In the example, monochromatic X-ray diffraction data f rom this high-pressure sample are sorted, but the algorithm is a gener al-purpose technique; it can also be used to sort single-crystal time- of-flight neutron diffraction data. Additionally, this method may be u sed to sort reflections from several crystal samples containing a mixt ure of materials. The algorithm is given in symbolic logic so that it can be translated and inserted into available crystallographic softwar e packages.