THE CRYSTAL STRUCTURE OF Cd₄GeSe₆, A II4 IV VI6 SEMICONDUCTING MATERIAL. J.M. Delgado*, J.A. Henao*, A.E. Mora** and M. Quintero**. *Departamento de Qumica and **Departamento de Fsica, Facultad de Ciencias, Universidad de Los Andes, Mrida 5101, Venezuela

X-ray quality single crystal fragments of Cd₄GeSe₆ were isolated from polycrystalline samples prepared by direct fusion of the elements in sealed, evacuated quartz ampoules. The stoichiometric proportion Cd:Ge:Se::2:1:4 was used because it was originally intended to prepare Cd₂GeSe₄, a II₂ IV VI₄ semiconductor, instead of the II₄ IV VI₆ finally obtained. The chemical composition of this phase was established using a Kevex EDX equipped Hitachi S-1250 SEM. The structural study carried out using single crystal diffraction techniques showed that this material crystallizes in the monoclinic space group Cc, with a=12.843(2), b=7.411(1), c=12.855(2), =109.85(1) and Z=4. Its structure can be described as a superstructure based upon a MgCu₂-type of structure. The superstructure nature of this material was deduced from Buerger precession photographs and confirmed in the structural analysis using the intensity data collected with a four-circle single-cystal x-ray diffractometer.

A detailed discussion of the different structure types reported for the II₄ IV VI₆ family of semiconductors is presented.This work was supported by CONICIT, Programa de Nuevas Tecnologas, Grant NM-18. JAH thanks UIS, Bucaramanga, Colombia for a fellowship.