Sei Ger Se2 on following 48Λ sites: Agl at 0.236, 0.236, 0.037 with 30.4% site occupation, Ag2 at 0.193,0.193,0.018 with 8.5% occupation and Ag3 at 0.165, 0.165, 0.009 with 21.3% occupation. In the present work both 11 and Se 1 were refined in split positions with regard to the regular 4a (0,0,0) and 16^(1/4, 1/4,1/4) sites leading to better atomic displacement parameters. Ag2 was refined anisotropically within an intermediate position (Ag2, Ag3 in previous X-ray study). The whole refinement

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... e better reliability factors and residuals. The structure which is disordered consists of well steady tetrahedral GeSe^ units and of slightly disordered Se 2and Γ anions. Owing to vacancies, the Ag + cations are highly disordered, that supports high mobility within the structure. For clarification in the figure, II and Sei atoms have been drawn on the regular (non split) 4a (0,0,0) and 16<?(l/4,1/4,1/4) sites. The tetrahedral anion is emphasized with Ge 1 -Se2 bonds. The possible diffusional paths for the disordered silver cations are schematized by representing Ag2-Ag2 distances within 2.33 Ä-2.47Ä. Agl atoms are symbolized by small circles. Abstract Ag 7 GeISe 5 , cubic, F43m (No. 216), a = 10.9864(7) Ä, V = 1326.1 A 3 , Ζ = 4, p m = 6.740 g em" 3 , Rgl(F) = 0.036, wRlef<F 2 ) = 0.088, 7-= 293 K.