Synthesis and crystal structures of CaY2Ge3O10 and CaY2Ge4O12

Abstract New compounds CaY 2 Ge 3 O 10 and CaY 2 Ge 4 O 12 were prepared by heating mixtures of CaCO 3 , Y 2 O 3 and GeO 2 at 1200 °C. CaY 2 Ge 3 O 10 is stable at 1300 °C, while CaY 2 Ge 4 O 12 decomposes into a melt and CaY 2 Ge 3 O 10 at approximately 1250 °C. We obtained single crystals of CaY 2 Ge 3 O 10 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 CaY 2 Ge 3 O 10 was determined by single crystal X-ray diffraction. CaY 2 Ge 3 O 10 crystallizes in the monoclinic space group P 2 1 / c with a = 6.0906 ( 8 ) , b = 6.8329 ( 8 ) , c = 18.752 ( 2 ) A and β = 109.140 ( 3 ) ° , Z = 4 , and R 1 = 0.029 for I > 2 σ ( I ) . In the structure of CaY 2 Ge 3 O 10 , Ca and Y atoms are situated disorderly in three 7-fold coordination sites between isolated germanate groups of triple GeO 4 tetrahedra, Ge 3 O 10 . The structural formula of CaY 2 Ge 3 O 10 is expressed as (Ca 0.45 Y 0.55 )(Ca 0.46 Y 0.54 )(Ca 0.09 Y 0.91 )Ge 3 O 10 . The crystal structure of CaY 2 Ge 4 O 12 was analyzed by the Rietveld method for the X-ray powder diffraction pattern. CaY 2 Ge 4 O 12 is isotypic with SrNa 2 P 4 O 12 , crystallizing in the orthorhombic space group P 4/ nbm , a = 9.99282 ( 6 ) , c = 5.06701 ( 4 ) A , Z = 2 , R wp = 0.092 , R p = 0.067 . CaY 2 Ge 4 O 12 contains four-membered GeO 4 -tetrahedra rings, Ge 4 O 12 . Eight-fold coordinated square-anitiprism sites and 6-fold octahedral sites between the layers of the Ge 4 O 12 rings are occupied by Y atom and Ca/Y atoms, respectively The structural formula is Y(Ca 0.5 Y 0.5 ) 2 Ge 4 O 12 .