Ce2Ti2SiO9 - the first titanate-silicate with cerium - Preparation, characterization, and structure

Ce2Ti2SiO9 was synthesized by chemical vapour transport in a temperature gr adient (1050 degrees C --> 900 degrees C) using Ce2Ti2O7 as precursor and a mmoniumchloride as transport agent. SiO2 was provided from the wall of the used silica tubes. The chemical composition of the crystals was determined by EDX and EELS analysis. The structure of Ce2Ti2SiO9 was determined and re fined to R1=0.025, (w)R2 = 0.067, respectively. The monoclinic phase crysta llizes in the space group C2/m (No.12) with a=16.907(3) Angstrom, b = 5.707 8(8) Angstrom, c = 7.574(2) Angstrom, beta = 111.38(2)degrees and Z = 4. Ti is octahedral, Si is tetrahedral surrounded by oxygen. Ce(1) is coordinate d by eight, Ce(2) by ten oxygen atoms. There are edge connected chains of T i(1)-O-octahedra parallel [010] which are connected along [001] with each o ther by Ti(2)-O-octahedra-pairs and Si-O-tetrahedra.