Two Non-centrosymmetric Cubic Seleno-germanates Related to CsCl-type Structure: Synthesis, Structure, Magnetic and Optical Properties


Two related non-centrosymmetric, cubic, quaternary chalcogenides, containing europium have been synthesized employing the molten flux method and by the reaction of europium halides with the ternary seleno-germanate, Na6Ge2Se6. The reactions of Eu, Ge and Se were accomplished in a molten Na2Se2 flux at 800 °C for 150 h in an evacuated fused silica ampoule and yielded Na2EuGeSe4 (I). Similarly, Na0.75Eu1.625GeSe4 (II), could be synthesized at slightly lower temperature (750 °C) with a different starting ratio of Eu, Ge, Se and Na2Se2. A reaction between EuCl3 and Na6Ge2Se6 in 1:2 ratio at 650 °C for 96 h in an evacuated fused silica ampoule yielded Na2EuGeSe4 (I), while the reaction between EuI2 and Na6Ge2Se6 in 1:1 ratio under similar conditions yielded Na0.75Eu1.625GeSe4 (II). Crystal data for these compounds are as follows: I, cubic, space group I4¯3m (no. 217), a=7.3466(3), Z=2; II, cubic, space group I4¯3d (no. 220), a=14.7065(8), Z=16. The crystal structures of I and II are closely related and can be compared to a CsCl-type and its ordered superstructure, respectively. These compounds are semiconductors with optical band gaps around 2 eV. The temperature dependence of the magnetic susceptibility indicated that both compounds are paramagnetic with μeff.=7.6 and 7.73 μB, for I and II, respectively, close to the theoretical value of 7.94 μB for Eu2+. Raman spectroscopic characterization of the compounds is also reported.



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