2 (tetragonal) (2). In the case of Ln Ο Ce, group P3m1, with a and c parameters varying from 3.9442 to Ce 2 (CO 3 ) 3 ΠΈ 8H 2 O was heated at 1273 K. For Ln Ο Eu, 3.7812 A Λand from 8.3609 to 8.2311 A Λ, respectively, as Ln atoms Eu 2 O 3 was calcined at 1023 K because the sample melted change from Ce to Gd. A choice of the space group was done above 1023 K. Chemical compositions of the products were assuming that the structure of Ln 2 O 2 CN 2 is like that of Ln 2 O 2 S. determined by CHN analyses and weight changes upon In this paper, structural parameters for both Ce 2 O 2 CN 2 and oxidizing the products to the corresponding oxides. Densi-Gd 2 O 2 CN 2 are not reported because the parameters for the ties of the products were measured using pycnometery. IR atoms did not converge to reasonable values. These compounds spectra were recorded on a Hitachi spectrophotometer have the layer structures which consist of the Ln 2 O 2Ψ 2 layers with the interlayer CN 2Ψ 2 ions. The Ln 2 O 2Ψ 2 layers are piled using the KBr method. Powder X-ray diffraction data were perpendicular to the c axis and the linear cyanamide ions, collected using a Rigaku RAD-RB diffractometer fitted Ψ NuCuN Οͺ , are inserted parallel to the c axis. Β© 1996 Academic with a graphite-monochromator employing CuKΝ° 1 radia-Press, Inc.
tion. All powder X-ray diffraction data were refined by the Rietveld method using RIETAN (5, 6). The diffraction data were collected in steps of 0.02Π over a range of 20Π-