The effect of pressure on atomic positions and lattice parameters is determined for trigonal Se under pressures from 0 to 86 kbar and for trigonal Te from 0 to 40 kbar by single-crystal x-ray diffraction using a diamond anvil high-pressure cell in a standard precession camera. The structural data confirm the lattice-dynamical homology that had been observed in the variation of the Raman frequencies at low pressures. However, the strongly nonlinear variations in the interatomic distances and the bond angles show deviations from a structural homology as the high-pressure phase transitions are approached.

• Received 12 April 1977

DOI:https://doi.org/10.1103/PhysRevB.16.4404