Starting from a general formula of scattering given by van Hove, effects of fluctuation or disorder in crystals on the intensity of diffuse scattering of X-rays, electrons and neutrons have been discussed. It is shown that the diffuse scattering can occur with or without a change in energy of radiation or particles and these scattering phenomena can afford different kinds of information on the fluctuation or disorder.
A general survey of the methods developed so far in making measurements of X-ray diffuse scattering from a single crystal is given. As a new technique, the method with a combination of an energy-dispersive detector and source of white X-ray radiation (Harada et al.: J. Appl. Cryst. 17, 1 (1984) ) is described in detail and the advantages and disadvantages of the method are discussed.
Diffuse scattering studies of structural phase transitions in electronically low-dimensional metals provide a clue to understand properties of the low-dimensional electron system because the structural change is brought about by instabilities of the electron system. A brief explanation is given for the mechanism of possible structural changes ; a charge-density wave formation, the Peierls transition, and the spin-Peierls transition. Examples are shown of experimental results obtained by X-ray diffuse scattering in several materials undergoing each kind of phase transitions.
There has been considerable interest in nucleation of a metastable phase called the omega phase cluster in certain alloys. The structure of the omega phase described as a sequence of displacements of the (111) planes in the parent bcc lattice and its characteristic diffraction profile are reviewed.
The kinetics of nucleation-growth process at first order phase transitions are discussed on the basis of Fokker-Planck equation. Critical divergence of the critical droplet size of the ordered domain has been derived. Experimental results on the atomic ordering process in Cu3Au alloy are described in comparison with the theoretical predictions. Existence of scaling law in terms of space and time concerning the growth process of the ordered domains has been suggested.
A brief review is given on the recent developments, both in theory and experiment, of the study of short-range-ordered structure of alloys. Particular emphasis is placed on the concept of microdomains which are thought of as a product of heterophase fluctuation existing in alloys and whose arrangements in a crystal space are strongly affected by the so-called Fermi-surf ace effects.
This paper reviews the diffuse scattering from the intercalant in the layered compound, i. e, graphite and transition metal dichalcogenides. X-ray results are mainly presented on the short-range order diffuse scattering from intercalated silver atoms in disordered stage-2 Ag0.18TiS2 at room temperature.
Recent study on the defect structures in transition metal monoxides VOx and NbO, and in stabilized zirconias Zr (Ca) O2-x and Zr (Y) O2-x has been reviewed. The diffuse scattering from VOx and TiOx was compared with the characteristic diffuse scattering observed in transition metal carbides and nitrides with NaCl-type structure. The reason for the existence of a large number of vacancies in transition metal compounds was explained in terms of their electronic structures. In addition, recent progress on the quantitative measurements and analyses of X-ray diffuse scattering from oxides has been stressed.
A diffraction method using recoilless γ-rays from a Mössbauer radioisotope source combined with a nuclear resonant absorber is described. This method makes it possible to separate experimentally the elastic from the inelastic part of the scattered radiations within the region of Bragg reflection with energy resolution up to 10-8 eV. Results of the applications to the studies of thermal diffuse scattering in Bragg reflection, Debye-Waller factor and dynamic structures in amorphous and crystalline solids are reviewed.
Significance of the neutron scattering in studies of diffuse scattering is shown by several examples. Selective observation of the dynamical fluctuations from the static disorder is emphsized in comparison with the X-ray and electron diffraction. Advantage of the neutron scattering is also indicated in mixed systems where neutrons afford good contrast.