CRYSTAL STRUCTURE OF CeNb3O9 AND LaNb3O9 BY X-RAY POWDER DIFFRACTION. M. E. Villafuerte-Castrejón, L. Carrillo-Avilés, A. Ibarra-Palos, Instituto de Investigaciones en Materiales Universidad Nacional Autónoma de México. A.P. 70-360, Ciudad Universitaria, México D.F. 04500 México, J. Duque, R. Pomés, Centro Nacional de Investigaciones Científicas. Apdo. 6990, Ciudad de la Habana, Cuba
Crystal structure of the perovskite type CeNb3O9 was characterized by X-Ray powder diffraction. Crystal structure of LaNbO3O9 was already reported but it was synthesized and characterized in the same conditions as the cerium compound in order to compare the data obtained, with regards to crystal structure.
Perovskite structure double oxides with formula LnNb3O9 have the Ln ions located in high symmetry sites which is important when studying spectroscopic properties. On the other hand, in this perovskite structure there are vacant Ln sites. It is interesting to provide information on the influence of defects on the stability of the crystal lattice and to look for the relationship between crystal structure and dielectric properties in those distorted perovskite structure.
The compounds were synthesized by solid state reaction and characterized by X-Ray powder diffraction. CeNb3O9 is orthorhombic, space group Pmmm, a= 3.898(4) Å, b= 3.917(2) Å, c= 7.876(6) Å, V=120.50(1) Å3, z = 2/3. LaNbO3O9 is also orthorhombic, space group Pmmm, a= 3.912(2) Å, b= 3.921(3) Å, c= 7.912(3) Å, V = 121.34(4) Å3, z = 2/3.
Crystal data were determined using the TREOR program. For crystal structures refinement the DBWS-9006PC program was used.