A review is given on the results of the structural studies of metals and alloys subjected to high pressures. Transition metals exhibit high resistance against compression and keep their atomic arrangements unchanged. An exception is found in iron, which undergoes a transition from the bcc to hcp-structure. Rare-earth metals have larger compressibility and their crystal structures change systematically following the sequence hcp→Sm-type→dbcp→fcc. Simple metals have still larger compressibility, but some of their crystal structures remain stable while the others show a variety of changes. In actinoid metals, only americium has a number of high-pressure polymorphs. Many of the Hume-Rothery alloys and L10-type alloys are stable under compression, whereas pressure significantly affects the stability of the long-period ordered alloy structures. Pressure-induced transition of amorphous alloys leads to the formation of new crystal structures.
Ferrielectric behaviour in ammonium sulfate has been studied by means of two methods. One of them is measurements of the temperature dependence of X-ray Bragg reflection intensities, and a qualitative interpretation of them was made. It is suggested that there are two kinds of independent order parameters. The other is crystal structure analyses of solid solutions (NH4) 2 (1-x) R2xSO4, R=K, Rb, Cs. Occupation parameters of the ammonium ions corresponding to the two kinds of the crystallographically independent cation sites were successfully obtained, which can explain the spontaneous polarizations of the solid solutions by using an expanded Kittel's antif erroelectric free energy. The improper f erroelectric-like free energy function previously proposed seems unnecessary.
The characteristic features of diamond microcrystals prepared by chemical vapor deposition are described. Scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Raman spectroscopy have revealed that these microcrystals include some imperfections, and show characteristic morphologies and surface microtopographies. They also contain high population of twinned particles.