(Ba, Sr)3MgSi2O8 structure change caused by Ba/Sr replacement

Crystal structure of BaxSr3-xMgSi2O8 has been determined by Raman spectroscopy and X-ray diffraction. The solid solution series have glaserite-type layered structures made of corner-sharing SiO4 tetrahedra and MgO6 octahedra. Ba2+ and Sr2+ ions are sandwiched in between the layers. Raman spectroscopy has found that structural symmetry changes at x = 0.5 and 2.5. Structural refinement by the Rietveld method has clarified that the symmetry changes occur among C2 (Z = 4), P (3) over bar m1 (Z = 1), and P (3) over bar (Z = 3). They originate in SiO4 tilting caused by size mismatch between alkaliearth cations and their site spaces. For x <= 0.5, SiO4 tilting occur every other interlayer space, whereas for x >= 2.5, all the SiO4 tilt. (C) 2014 International Centre for Diffraction Data.