The anomalous X-ray scattering (AXS) method has recently received much attention for analyzing the disordered materials. This paper discusses the fundamentals of AXS method and its potential power for determining the local chemical environment around a specific element as a function of radial distance. The usefulness of this method was demonstrated with the some selected examples of GeO2-P2O5 glasses, amorphous CoFe2O4-x thin film and amorphous ZrO2.
It was recently found by X-ray crystallography that inclusion crystals of cholic acid, a typical steroidal bile acid, have a high ability of the molecular recognition for many guest molecules. We review here the nature of cholic acid inclusion crystals in the following aspects: 1) channel type inclusion crystals formed by layered arrangements of cholic acid, 2) crystals without any guest molecules, 3) intercalation phenomena of no-guest crystals with the guest solutions, and 4) chiral recognition of lactones by cholic acid crystals.
The growth of hen egg-white lysozyme crystals over 28 days is followed by photographs, together with the accompanying concentration decrease in the supernatant. The concentration change is shown to be approximated by a theoretical curve derived from a set of simple differential equations. The concentration reaches a constant value after a few months, which is the solubility of the crystals. The solubility changes greatly with temperature, which reflects the enthalpy change upon crystallization. The length (L) and width (W) of a tetragonal crystal are also measured as a function of time. The change in L was greater than that of W, thus explaining the cause of the variation of the crystal morphology. These results, i.e. the kinetic equations, solubility diagrams, and morphogenesis, are examples of the rules underlying the growth of protein crystals.
This article is concerned with the recent controlling techniques of mean size, structure and heterojunction of monodispersed fine particle as modern advanced materials. For the control of mean size, the general principle and a theoretical and experimental approach to quantitative control of the mean size are introduced. Also, the relationship between particle shape and the structure is discussed and a rather new idea of polymerize growth mechanism for the growth of metal oxides is referred to. Finally, one of the most sophisticated particles, heterojunctioned particles, is introduced and the mechanism of the formation of junctioned particles consisting of a silver chloride host and silver bromide guests is delineated as an example.
The anisotropic mean square displacements, (‹u2›), of atoms in β-quartz, calculated for a simple force constant model of an ordered structure were in an excellent agreement with the experimentally determined ones in the normal structure analysis, for both magnitude, and orientation of principal axes of ellipsoids. The force constants were determined via observed phonon frequencies, and hence the agreement of the observed ‹u2› with the calculated ones shows that the order-model of β-quartz is a sufficient one in explaining the anisotropic thermal parameters. In another word, the split-atom model, which was previously taken in a neutron diffraction study, is not a unique candidate for modelling such highly anisotropic thermal parameters. The present study emphasizes that thermal parameters obtained in structure analyses are usable in quantitative discussions of crystal structures with computational methods such as lattice dynamics or else.
The atomic structure of a Ga2Se3 epilayer grown on a (100) GaAs epilayer by molecular beam epitaxy (MBE) is studied by transmission electron microscopy and diffraction. A highly developed pseudo-two-dimensional ordering of structural vacancies is found in the interfacial region of the Ga2Se3 epilayer. The interfacial ordered structure is described as follows. Vacancies form c (2×2) ordered arrangements in the first (100) Ga layer of Ga2Se3. Ga atoms almost fully occupy the second Ga layer. The c (2×2) arrangements of vacancies are locally formed in the third Ga layer with a shift of a/2  with respect to the location of the first Ga layer, where a is the unit cell size of disordered Ga2Se3. The structure model derived in this study suggests that the chemical bond mismatch at the Ga2Se3/GaAs interface plays an essential role in the formation of the interfacial ordering.