Features and Relationship between Some Methods of X-ray Diffraction Analysis for Amorphous Materials

Two fundamental methods have been used for X-ray structure analysis of amorphous materials, i.e., the intensity comparison method and radial distribution analysis. There is an opinion that Fourier conversion from raw intensity data to a radial distribution function (RDF) introduces some errors and a comparison on intensity curves is, therefore, more exact. The present calculations have indicated that an RDF obtained from an intensity curve can be exactly re-transformed to the original intensity curve, if the upper range of Fourier-integral is sufficiently high. This means that no information disappears or any other spurious information is not added in the process of transformation between intensity data and an RDF. On the other hand, direct calculation of intensity with the Debye equation inevitably introduces truncation errors, unless some approximations are used. When the comparison on intensity curves is requested, it is desirable to transform an RDF obtained from a structure model to an intensity curve. Some distortions introduced in RDFs are offset each other in an observed and calculated RDFs and usually need not to be considered in the pair function method. There is, however, another opinion that some distortions introduced in RDFs difuse the part of small atomic distances and a comparison in intensity curves is, therefore, necessary. The present calculations indicate that atomic pairs with small inter-atomic distances can be equally compared in RDFs as well as in intensity curves as for oxide, chalcogenide or halide glasses. In conclusion, the present calculations have proved that errors are not intermixed in transformation process between an intensity curve and an RDF and that the same level of assessment of the structural models is possible either in intensity curves or in RDFs, although the intensity comparison method by use of the Debye equation can not avoid the intermixture of truncation errors, unless some approximations are used.