CRYSTAL-STRUCTURE AND THERMAL-EXPANSION OF CA2Y2SI2O9

The crystal structure of Ca2Y2Si2O9 was studied by X-ray and electron diffraction. Statistical atomic site positions were determined in an o rthorhombic cell, a = 10.453(3), b = 3.720(2), c = 10.290(2) Angstrom, space group Pnma. The local structure of Si2O7 silicate anions was il lustrated from the refined atomic positions. The Ca2Y2Si2O9 structure could be explained by locally disordered arrangement of Y4Al2O9 monocl inic structure. The linear thermal expansion coefficient of Ca2Y2Si2O9 ceramics measured by dilatometry was 9.3 X 10(-6) degrees C-1 from ro om temperature to 1500 degrees C. (C) 1998 Elsevier Science Ltd.