Synthesis and crystal structures of CaY2Ge3O10 and CaY2Ge4O12

New compounds CaY2Ge3O10 and CaY2Ge4O12 were prepared by heating mixtures of CaCO3, Y2O3 and GeO2 at 1200 °C. CaY2Ge3O10 is stable at 1300 °C, while CaY2Ge4O12 decomposes into a melt and CaY2Ge3O10 at approximately 1250 °C. We obtained single crystals of CaY2Ge3O10 by cooling a sample with an initial composition of Ca:Y:Ge=1:2:8 from 1300 °C with a rate of −6 °C/h. The crystal structure of CaY2Ge3O10 was determined by single crystal X-ray diffraction. CaY2Ge3O10 crystallizes in the monoclinic space group P21/cP21/c with a=6.0906(8)a=6.0906(8), b=6.8329(8)b=6.8329(8), c=18.752(2)Å and β=109.140(3)°β=109.140(3)°, Z=4Z=4, and R1=0.029R1=0.029 for I>2σ(I)I>2σ(I). In the structure of CaY2Ge3O10, Ca and Y atoms are situated disorderly in three 7-fold coordination sites between isolated germanate groups of triple GeO4 tetrahedra, Ge3O10. The structural formula of CaY2Ge3O10 is expressed as (Ca0.45Y0.55)(Ca0.46Y0.54)(Ca0.09Y0.91)Ge3O10. The crystal structure of CaY2Ge4O12 was analyzed by the Rietveld method for the X-ray powder diffraction pattern. CaY2Ge4O12 is isotypic with SrNa2P4O12, crystallizing in the orthorhombic space group P4/nbm  , a=9.99282(6)a=9.99282(6), c=5.06701(4)Å, Z=2Z=2, Rwp=0.092Rwp=0.092, Rp=0.067Rp=0.067. CaY2Ge4O12 contains four-membered GeO4-tetrahedra rings, Ge4O12. Eight-fold coordinated square-anitiprism sites and 6-fold octahedral sites between the layers of the Ge4O12 rings are occupied by Y atom and Ca/Y atoms, respectively The structural formula is Y(Ca0.5Y0.5)2Ge4O12.

Crystal structure of CaY2Ge3O10 showing Ge–O4 tetrahedra (Ge3O10 group).Figure optionsDownload as PowerPoint slide