Structural Characterization and Polymorphism of R2BaNiO5 (R = Nd, Gd, Dy, Y, Ho, Er, Tm, Yb) Studied by Neutron Diffraction

✍ Scribed by E. Garcı́a-Matres; J.L. Martı́nez; J. Rodrı́guez-Carvajal; J.A. Alonso; A. Salinas-Sánchez; R. Saez-Puche

• Publisher: Elsevier Science
• Year: 1993
• Tongue: English
• Weight: 406 KB
• Volume: 103
• Category: Article
• ISSN: 0022-4596
• DOI: 10.1006/jssc.1993.1107

✦ Synopsis

The fimily of compounds (R_{2}) Bakios ((R=\mathrm{Nd}), Dy, Y, Ho. Fr, Tm, Yb) has been studied by neutron powder diffraction il reom temperature. All of them presen orthorhombic symmetry (space group (/ \mathrm{mmm}). (Z=2) ). The main leat ure of these materials is the existence of one-dimensional chains of vertex-sharing (\mathrm{NiO}_{5}) octahedra along the (a)-axis. The present research has revealed the effect of the size of the rare earth ions on the structural paramelers, which plays a role nearly equivalent to a hydrostatic "chemical pressure" in the geometric distotion of the structure. The volume of the (\mathrm{Ni}) and Ba polyhedra varies linearly vs the ionic radius of the rare earth. The overall agreement between the valence bond sums and formal charges is very poor. This fact indicates that the present structure is under very high internal stress and may be melastable. We speculate that there may exist a dimorphism in the other members of this family of oxides, similar to that already found for the Tm. Yb, and Lu compounds. O 1993 Academic Press. Inc.