2 NEW POLYMORPHS OF SISE2 - STRUCTURAL INVESTIGATION BY RAMAN AND SI-29 MAS NMR SPECTROSCOPIES AND RELATIONSHIP WITH THE STRUCTURE OF VITREOUS SISE2

Two new polymorphs of SiSe2 can be synthesized by low-temperature reaction of the elements at 400 and 500-600-degrees-C, respectively. Their characterization by X-ray powder diffraction, Raman and Si-29 MAS NMR spectroscopies is described. In contrast to the known phase of SiSe2, whose structure consists of infinite chains of edge-sharing tetrahedra, these new polymorphs contain certain amounts of corner-sharing tetrahedra as well. The latter feature illustrates a rather uncommon case for a non-oxide system, where the local structures in the crystalline and glassy states closely resemble each other.