|
Developing new materials it is often necessary to deal with the identification of new, previously unknown phases that were formed during the synthesis. Regardless of the type of synthesis (arc melting, chemical reaction, reaction sintering, coating deposition, etc.), just the complete information about the phase composition of the synthesis products contributes to the targeted adjustment of technological parameters. Thus, the express phase analysis of the material with the identification of all phases formed in the sample studied (including phases synthesized for the first time) is one of the most important tasks at developing the synthesis technology of any new material. The easiest way to identify a previously unknown phase is to search for the availability of its structural analogues in the literature. To increase the efficiency and automation of the search for such data, the Department of Metal Physics has created a database of crystal structures of intermetallic and inorganic compounds. Currently, it contains about 30,000 units of information (by data of more details). The software developed also allows effective use of this database for phase analysis (more details) and at studying the crystal structure of phases (more details). According to the proposed method, the search for possible analogous structures in automatic mode is carried out by comparing the diffraction patterns of the new phase studied with the diffraction pattens of each of the compounds available in the database. That is, the search is carried out by comparing the positions of the characteristic diffraction peaks of the phase studied and the phase of the data DataBase, or, in fact, by comparing the position of the reference reflections of these diffractograms. The input information for the search is a set of diffraction reflections of the compound studied (the positions of the peaks and the values of their integral intensities). The object of a search is a set of reference reflections of the compounds from a database. Search for possible analogous structures is carried out in an automatic mode according to all elements of the database. In this case, the criterion for selecting an analog structure from the database is the reliability factor, which is calculated using a formula similar to that for structural calculations. In this case, the interplanar distance of the strongest reflection of the database compound is equal to the interplanar distance of the strongest reflection of the compound studied, and all other interplanar distances of reflections of this compound are recalculated taking into account the available shift. If the reliability factor does not exceed the value specified by the user, then the image of the analog compound from the database is already compared in graphic mode with the experimental diffraction pattern of the compound studied. In case of their coincidence, the diffraction pattern of the compound studied is indexed using the complete data on crystal structures of the analog structures that were selected as a result of the search. Then its structure is checked for belonging to a certain structural type by the X-ray structural analysis methods. Approach described above allows us to significantly simplify the procedure of determining the crystal structure of a newly synthesized compound (especially if it is present in the synthesis product as an additional phase), and, as a result, to some extent reduce the time for optimizing the technological modes of material synthesis .
All programs of the software used for creation of the DataBase of structural characteristics of intermetallic and inorganic compounds, as well as the for DataBase of diffraction images of these compounds are original developments. The program texts (including graphic modules) are prepared in FORTRAN (PowerStation FORTRAN v. 4.0 compiler) for Windows operating system (versions 95, XP and higher). . Note that the file with crystallographic characteristics of the compounds of DataBase is included at the program level in structural calculations (more details) and quantitative phase analysis (more details) program complexes. This makes possible to quickly use the specified information at quantitative phase analysis, predicting new structural models, refining the crystal structures of the corresponding compounds in samples of the materials studied and in coatings, as well as for determining the predominant orientation (texture) (more details) in film coatings. The program of the DataBase of structural characteristics of compounds provides the following capabilities: 1. Search for information about the crystal structure of an intermetallic or inorganic compound by two key elements (elemental composition of the compound, space symmetry group) and visualization (printing) of the search result. (more details) 2. Processing of the diffraction patterns for selected compound on any of the most common radiations (Cu, Fe, Co, Cr, Ni, Mo), which can be presented in a table or in a graphical form (more details) 3. Visualization of images of projections of crystal structure for the selected compound onto the XY, XZ, YZ planes; as well as preparation of a .cry file for this structure for further work with it in the Diamond program. (more details)
|