Structural Properties of GeSe2 at High Pressures

Crystalline and glassy GeSe{sub 2} have been subjected to pressures up to 7.7 GPa and temperatures up to 1,100 C using a high-pressure belt-type apparatus. Two high-pressure crystalline polymorphs of GeSe{sub 2} have been synthesized. The crystal structure of the tetragonal form of GeSe{sub 2} prepared at 3.0 GPa and 500 C, with space group I-42d and a = 5.7307(4) and c = 9.691(1), was determined by means of powder X-ray diffraction data. The structure consists of GeSe{sub 4} tetrahedra that share corners in a three-dimensional network and has a considerably higher density than the two-dimensional structure of ambient-pressure GeSe{sub 2} consisting of both edge- and corner-sharing tetrahedra. The IR and Raman spectra of tetragonal GeSe{sub 2} are discussed in relation to the structure of GeSe{sub 2} glass. An orthorhombic polymorph of GeSe{sub 2} was formed during quenching from 7.7 GPa and 500 C. Amorphous GeSe{sub 2} compressed at 250--300 C was observed to partly crystallize at 3.0 and 7.7 GPa. 22 refs., 4 figs., 4 tabs.

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