Structural transformations in three-dimensional crystalline GeSe2 at high pressures and high temperatures

Germanium diselenide GeSe2 is studied in situ at the pressure range 2-6 GPa using angle-dispersive X-ray diffraction in a large volume Paris-Edinburgh cell. The structure at 2 GPa and 698 K, solved with direct methods in the 14 space group (a = 5.5073(3) Angstrom, c = 9.9373(8) Angstrom, Z = 4), is three dimensional with all the GeSe4 tetrahedra sharing their corners. Anomalous lattice expansion along the c axis with increasing pressure and pressure-induced structural variations are explained by anisotropic lattice distortions due to cooperative tiltings of the rigid GeSe4 units. (C) 2000 Academic Press.