Recent researches on f erroelastic materials are briefly reviewed. A crystal is f erroelastic if it has two or more stable states with respective spontaneous strains and it can be transformed among these states by an application of mechanical stress. Ferroelasticity is a phenomenon which is widely spread and is sometimes accompanied by other phenomena such as ferroelectricity, magnetic-ordering and superconductivity. A few examples of f erroelastic materials are given, and some related aspects of physical significance are briefly summarized.
Since 1935, a great number of crystal structures have been solved by the Patterson technique and recently the symbolic addition procedure is becoming a major crystallographic tool, especially for organic compounds with no heavy atom. To solve the crystal structure without any human intervention the auther has constructed a large program system which has been made up of several crystallographic computer programs. It is intended for use by organic chemists rather than professional crystallographers. The program system, written in FORTRAN-63 for a CDC 6600 computer with a 131 K core strage and 60-bit word-length, may be run either separately or in combination. The input data are the highest E reflexions (|E|>1. 5, E being normalized structure factor), cell constants, symmetry card, atomic scattering factor tables, and number and types of atoms in the unit cell. The outputs are a projection diagram of the molecules in a unit cell, atomic co-ordinates and bond distances. The program system has been successful over a considerable range of space groups.
Dislocation-free InP and GaAs crystals have been grown by a liquid encapsulationtechnique by means of an impurity doping procedure. It was found that grown-indislocations were diminished, when a certain kind of impurities was added into themelt from which crystal was pulled. Impurity effect on grown-in dislocation density was examined for Zn, S and Te inInP, and for Zn, S, Te, Al and N in GaAs. It was found that these impurities wereeffective for reducing grown-in dislocation density, except for Zn in GaAs. Effectiveness of impurity for reducing the grown-in dislocation density was ascribedto strength of bonds formed between the substitutional impurity atoms and host crystalatoms surrounding the impurity atoms.