Crystal growth, structure, crystalline perfection and characterization of zinc magnesium ammonium sulfate hexahydrate mixed crystals Zn_xMg_((1-x))(NH_4)_2(SO_4)_2 • 6H_2O

摘要

Mixed crystals Zn_xMg_((1_x))(NH_4)_2(SO_4)_2-6H_2O of the two well-known Tutton's salts Zn(NH_4)_2(SO_4)_2 • 6H_2O and Mg(NH_4)_2(SO_4)_2 • 6H_2O were grown with varying molar proportions (x=0.10-0.90) by slow evaporation solution growth technique. The mixed crystal Zn_(0.54)Mg_(0.46)(NH_4)_2(SO_4)_2 • 6H_2O is crystallizing in monoclinic system with space group P2_1/c and cell parameters α=6.2217(4)A, b=12.5343(7) A, c=9.2557(6) A, β= 106.912(3)°. The coexistence of zinc and magnesium ions in the mixed crystal was confirmed by inductively coupled plasma (ICP), atomic absorption spectroscopy (AAS) and energy dispersive X-ray spectroscopy (EDS). Compositional dependence of lattice parameters follows Vegard's relations. Slight variations are observed in FT-IR and XRD of pure and mixed crystals. Comparison of crystalline perfection as evaluated by high-resolution X-ray diffraction (HRXRD) for mixed crystals of various proportions reveals a reasonably good crystalline perfection for the mixed crystal with nearly equimolar ratio of Zn and Mg. The surface morphology of the mixed crystals changing with composition was studied by scanning electron microscopy (SEM). UV-vis studies reveal that the transparency of the mixed crystals was not much affected.