A coincidence site lattice (CSL) model is applied t o analyse the boundary structures of Laves phase alloys, Mg (Al0.5 Cu0.5) 2 and Mg (Cu1-x Znx) 2.All the origins in every layer are adopted as lattice points to draw interpenetrating lattices. Due to this extention, the interpenetrating lattices give characteristic CSL-patterns which predict not only detailed ordered structures inside a period appearing at the boundary but also predict smaller DSC-vectors which are Burgers vectors of boundary dislocations. The CSL-patterns as well as the DSC (displacement - shift - complete) - lattices are demonstrated for various layer structures, in order to interpret high resolution electron micrographs of the boundaries of the Laves phase alloys.
A recent crystallographic study of the photosynthetic reaction center from a purple bacterium has been reviewed. The three-dimensional structure has been elucidated in consequence of the first success in crystallization of membrane proteins and in crystallography of extremely large protein complex. The molecular mechanism of electron transport system in the primary step of photosynthesis has been revealed on the basis of the present structure. For this work, the Nobel prize for chemistry in 1988 was awarded to J.Deisenhofer, R.Huber and H.Michel.
The Maximum Entropy Method to obtain Electron Density Distribution Map (EDDM) of crystals is outlined. In the method, the particular attention is paid to treat the powder diffraction data. By using the method, three-dimensional EDDM of silicon is drawn from the 30 structure fact ors determined accurately by Saka and Kato [T.Saka & N.Kato: Acta Cryst. A42, 468 (1986) ] . The EDDM of CeO2 obtained from powder data is also shown. It is found that the EDDM drawn by the MEM can reveal details of electron density distribution in solid state such as chemical bonding and electrons in vacant sites.