Crystal structures at megabar pressures determined by use of the cornell synchrotron source.

X-ray diffraction studies have been carried out on alkali halide samples 10 micrometers in diameter (volume 10(-9) cubic centimeter) subjected to megabar pressures in the diamond anvil cell. Energy-dispersive techniques and a synchrotron source were used. These measurements can be used to detect crystallographic phase transitions. Cesium iodide was subjected to pressures of 95 gigapascals (fractional volume of 46 percent) and rubidium iodide to pressures of 89 gigapascals (fractional volume of 39 percent). Cesium iodide showed a transformation from the cubic B2 phase (cesium chloride structure) to a tetragonal phase and then to an orthorhombic phase, which was stable to 95 gigapascals. Rubidium iodide showed only a transition from the low-pressure cubic B1 phase (sodium chloride structure) to the B2 phase, which was stable up to 89 gigapascals.

Preparation of micron thick specimens for high pressure study.

The electrical resistance behavior of a material under very high pressure can be studied by pressing the material with a diamond indentor against a diamond flat. The high pressures generated can be calculated using Hertz's theory provided the material thickness is about a micron or less. Here we describe a method of preparing micron thick specimens of a few millimeters in size. We have prepared micron thick specimens of a few millimeters in size of Si (100), Si (111), NaCl (100). The result of high pressure study on Si (100) is also presented.

High pressures on small areas.

Small diamond indentors with spherical tips were pressed against a polished diamond flat. Pressures were calculated from Hertz contact theory. Very high pressures were achieved on small areas.