STRUCTURAL STUDY OF THE HIGH-PRESSURE PHASES OF BISMUTH USING HIGH-ENERGY SYNCHROTRON-RADIATION

An x-ray diffraction study was carried out on the crystal structure of the high pressure phases of bismuth, Bi III, Bi III', and Bi IV, using high-energy monochromatic synchrotron radiation from the TRISTAN Accumulation Ring (6.5 GeV). Powdered samples were compressed in a cubic-type multianvil press MAX80 at pressures ranging from 3 to 6 GPa. In some compression runs, the sample temperature was raised up to 550 K. It was possible to obtain diffraction patterns containing many diffraction peaks and assign unambiguously indices to them. The crystal structure of Bi III is tetragonal with ten atoms contained in the unit cell. It has been shown that, when pressure is increased across the transition pressure between Bi III and Bi III', no change in the diffraction pattern takes place, indicating that the two phases have the same structure. Bi IV which exists in the high temperature region in the P-T diagram has been shown to have the structure with a monoclinic symmetry and eight atoms in the unit cell. All the structures determined can be regarded as a distorted body-centered-cubic lattice structure. © 1995 American Institute of Physics.