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 I43m (no. 217), a=7.3466(3), Z=2; II, cubic, space group I43d (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 μ B for Eu2+. Raman spectroscopic characterization of the compounds is also reported.



Keywords and Phrases

Crystal Structure; Fused Silica; Magnetic Properties; Magnetic Susceptibility; Optical Properties; Synthesis (Chemical); Ternary Alloys; Chalcogenide; CsCl Type; Superstructure; Semiconducting Germanium Compounds; Chalcogenide; CsCl Type; Europium; Semiconducting; Superstructure

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