Abstract
Abstract Compound formation in the Ce2O3-SiO2 system in air and in a reducing atmosphere was investigated using the spray dry technique. Compounds with three different compositions were found, i.e. Ce2SiO5, Ce4.67Si3O13 and Ce2Si2O7. In contrast to Ce2Si2O7, the high temperature stability of Ce2SiO5 and Ce4.67Si3O13 in air was measured to be low, explaining why they cannot be obtained in air. Ce2SiO5 has a monoclinic unit cell ( a=9.282 A , b=7.390 A , c=6.972 A and β=108.33°). Its volume fits well into the α-Ln2SiO5 series (Lnlanthanide). Ce4.67Si3O13 has an apatite-like structure with a hexagonal unit cell ( a=9.657 A and c=7.121 A ). For Ce2Si2O7 two different modifications were found. The first is the already known high temperature modification (G type) with an orthorhombic unit cell ( a=8.722 A , b=13.056 A and c=5.401 A ). The second is a low temperature modification (A type) never reported before with a tetragonal unit cell ( a=6.799 A and c=24.734 A ). Its volume fits well into the A-Ln2Si2O7 (L=lanthanide) series.
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