tailieunhanh - ANOMALOUS X-RAY SCATTERING FOR MATERIALS CHARACTERIZATION

Structural Characterization of Crystalline and Non-crystalline Materials – A Brief Background of Current Requirements The X-ray powder diffraction technique is a well-established and widely used method for both qualitative and quantitative analysis of various substances in a variety of states (see, for example, [1]). However, in a multi-component mixture with a relatively complicated chemical composition, we frequently find difficulty in identifying the individual chemical constituents by the conventional X-ray powder diffraction method. There are also generally insufficient differences in the X-ray diffraction intensities for two elements of nearly the same atomic number in the periodic table. For example, this is certainly. | 1. Structural Characterization of Crystalline and Non-crystalline Materials A Brief Background of Current Requirements The X-ray powder diffraction technique is a well-established and widely used method for both qualitative and quantitative analysis of various substances in a variety of states see for example 1 . However in a multi-component mixture with a relatively complicated chemical composition we frequently find difficulty in identifying the individual chemical constituents by the conventional X-ray powder diffraction method. There are also generally insufficient differences in the X-ray diffraction intensities for two elements of nearly the same atomic number in the periodic table. For example this is certainly the case for a mixture of copper sulfide and ferrite components in the products of a copper smelting process. Ferrites are a group of compounds with spinel structure 2 expressed by the general formula MFe2 O4 where M is a divalent cation. They are known to have very interesting electrical and magnetic properties which are controlled by the distribution of cations between different sites. Substituting one element for another is very common in materials processing for controlling new functional properties of specific compounds. A clear understanding of the physical and chemical properties of such oxide materials depends heavily on their atomic-scale structure. In such ferrite materials described by the spinel structure there are 32 octahedral and 64 tetrahedral interstices formed by oxygen atoms available for cations in a unit cell and half of the octahedral sites and one-eighth of the tetrahedral sites are known to be occupied. For example a divalent zinc cation Zn2 usually prefess the tetrahedral sites in zinc ferrite ZnFe2O4 and is Iff the normal type 3 . On the other hand magnetite Fe3O4 ĨS classified as inverse spinel where the tetrahedral sites contain only ferric ion Fe3 the residual Fe3 and ferrous Fe2 ions are cttal d cooedinafed at low .