Ab initio study on structure and phase transition of A- and B-type rare-earth sesquioxides Ln2O3 (Ln = La-Lu, Y, and Sc) based on density function theory

Ab initio energetic calculations based on the density functional theory (DFT) and projector augmented wave (PAW) pseudo-potentials method were performanced to determine the crystal structural parameters and phase transition data of the polymorphic rare-earth sesquioxides Ln(2)O(3) (where Ln = La -Lu, Y, and Sc) with A-type (hexagonal) and B-type (monoclinic) con. gurations at ground state. The calculated results agree well with the limited experimental data and the critically assessed results. A set of systematic and self-consistent crystal structural parameters, energies and pressures of the phase transition were established for the whole series of the A-and B-type rare-earth sesquioxides Ln(2)O(3). With the increase of the atomic number, the ionic radii of rare-earth elements Ln and the volumes of the sesquioxides Ln(2)O(3) reflect the so-called lanthanide contraction''. With the increase of the Ln(3+) -cation radius, the bulk modulus of Ln(2)O(3) decreases and the polymorphic structures show a degenerative tendency. (C) 2007 Elsevier Inc. All rights reserved.