Department of Earth and Planeraty Science, Hokkaido University
○HIROYUKI MIURA

In order to study an unknown crystal structure by the Rietveld method, a correct structure model must be prepared in advance. This is usually very difficult when no information is available about the structure. A newly developed program, which automatically constructs a crystal structure model of the object-material, would simplify the process of solving the structure of the powdered material. This program requires XRD data, cell constants, a space group, a chemical formula, and a Z-number (the number of the formula in a unit cell). On the basis of atomic positions selected by the Monte Carlo method, this program calculates the R-factor of the model from theoretical and observed XRD data. Hundreds of models of a low R-factor are selected and stored. Then, they gradually converge to a true structure. Using this program and a personal computer, several unknown crystal structures could be solved, which demonstrates that this method is a powerful tool to solve the simple crystal structure of powder materials.