Pressure apparatus of split-octahedron type for x-ray diffraction studies.

An apparatus of split-octahedron type has been developed for the study of x-ray diffraction at high pressure. The apparatus consists of a cylinder, a sphere, and an octahedron, all split up and assembled in a multistaged arrangement. Three ways of splitting the innermost octahedron are utilized in matching the cell geometry to the standard camera method. High pressures in excess of 220 kilobars can be generated in the center of the split octahedron by using a composite mixture of diamond powder and epoxy resin as a pressure-transmitting medium. The pressures required for the semiconductor-to-metal transitions of ZnTe, ZnS, GaAs, and GaP are determined by simultaneously monitoring the electrical resistance of the semiconductors and the lattice parameter of sodium chloride.