SPECTROSCOPIC STUDIES, THEORETICAL-MODELS AND STRUCTURAL CHARACTERIZATION - II - SYNTHESIS AND X-RAY-POWDER DIFFRACTION OF THE ELPASOLITES CS2NASMCL6

In this research work, we report the synthesis and structural characte rization of the stoichiometric elpasolite Cs2NaSmCl6. The synthesis wa s performed under a solid state reaction in nitrogen atmosphere from t he chemicals CsCL, NaCl and SmCl3 weighted stoichiometrically. The bes t possible crystallization temperature was obtained using thermal stud ies of the type DTA/TGA (the thermal treatment was allowed to proceed for 2.5 hours at 755 degrees C, showing a temperature gradient of 10 d egrees C/minute). The structural characterization by powder X-ray diff raction (XDR) indicates that this elpasolite belongs to the Fm3m(O-h(5 )) space group and the optimized structural parameters are as follows: a(o) = 10.8342 Angstrom, V = 1271.72 Angstrom(3), Z = 4, M = 651.88, D-x = 3.406 and D-exp = 3.41 +/- 0.01. The profil refinement, using th e Rietveld method, allowed us to fit the experimental and the calculat ed intensities of a total of 32 lines. The above result indicates that the condition R-exp < 2R(wp) is fulfilled, and the crystallographic p arameters obtained in the current work have a noticeable accuracy. The structure of this elpasolite shows closed cubic packing made up from Cs2+ + 3Cl(1-) and the counter ions filling the octahedral holes, in f ull agreement with anti fluorite type crystal. According to the above description, these elpasolite adopt the form (M(1/3)square(2/3))(4)X-2 , where M labels the central metal, X stand for the Chlorine ions and square represent the vacancies, which may accommodate a significant am ount of defects without collapsing. This experimental study provides t he necessary input to test theoretical models against experimental dat a.