Synthesis and crystal structures of CaY₂Ge₃O ₁₀ and CaY₂Ge₄O₁₂

New compounds CaY₂Ge₃O₁₀ and CaY ₂Ge₄O₁₂ 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 CaY ₂Ge₃O₁₀ 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 CaY₂Ge ₃O₁₀ was determined by single crystal X-ray diffraction. CaY₂Ge₃O₁₀ crystallizes in the monoclinic space group P21/c with a=6.0906(8), b=6.8329(8), c=18.752(2)Å and β=109.140(3)°, Z=4, and R1=0.029 for 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 (Ca_0.45Y_0.55)(Ca_0.46Y_0.54) (Ca_0.09Y_0.91)Ge₃O₁₀. The crystal structure of CaY₂Ge₄O₁₂ was analyzed by the Rietveld method for the X-ray powder diffraction pattern. CaY₂Ge ₄O₁₂ is isotypic with SrNa₂P₄O ₁₂, crystallizing in the orthorhombic space group P4/nbm, a=9.99282(6), c=5.06701(4)Å, Z=2, Rwp=0.092, Rp=0.067. CaY ₂Ge₄O₁₂ contains four-membered GeO ₄-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(Ca_0.5Y _0.5)₂Ge₄O₁₂.