STRUCTURE STUDY OF SOME LANTHANIDE'S OXIDES BY X-RAY DIFFRACTION AND PAIR POTENTIAL MODELING

Abstract

A number of Lnx Oy rare-earth oxides where Ln = La, Ce, Pr, Nd, Sm, Eu, Tb,
Dy and Er, x=1, 2, 4, 6 and y=2, 3, 7, 11 have been studied by powder
diffractometry and pycnometry coupled with the simulation of their lattice
dimensions by empirically derived pair potentials using the GULP code.
Crystallographic analysis showed the oxides exist in the tri, tetra and mixed tri-tetra
valency with Bravias lattices: hexagonal- P, cubic- I and cubic- F as a result of the
oxidation state assumed by the Ln element that may be caused by the nature of the
oxide or preparation process involved. Unit cell volumes of the oxides that exhibit
identical Bravias lattices reflect a behavior that can be correlated with the atomic
number of the Ln element whereby it decreases linearly by uncertainty not
exceeding ca. 3%. The average bond lengths of Ln - O polyhedra in the sesquioxides
(Ln2 O3) space group Ia3 also follow suit. The behavior is interpreted on a
phenomenon known as lanthanide contraction.