High-pressure Cmca and hcp phases of germanium

作者：K. Takemura, Ulrich T. Schwarz, K. Syassen, Michael Hanfland, N. E. Christensen, D. L. Novikov, I. Loa · 发表于：Physical review. B, Condensed matter · 年份：2000 · DOI：10.1103/physrevb.62.r10603 · 被引用次数：77 · 研究领域：High-pressure geophysics and materials、X-ray Diffraction in Crystallography、Crystal Structures and Properties

Structural phase transitions of germanium at pressures up to 190 GPa have been investigated by means of angle-dispersive x-ray powder diffraction using synchrotron radiation. Near 100 GPa the primitive hexagonal modification of Ge transforms to an orthorhombic phase with 16 atoms per unit cell. The results of full-profile Rietveld refinements in space group $\mathrm{Cmca}$ indicate that the orthorhombic modification of Ge is isotypic to the phase Si-VI. Near 160--180 GPa Ge undergoes a transition to a structure assigned as hexagonal close packed (hcp). Ab initio calculations of pressure-dependent enthalpies and optimized structural parameters are presented for different structures of Ge. The calculated results clearly support the observed occurrence of the $\mathrm{Cmca}$ structure in Ge.