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 Ln2O3 (where Ln=La–Lu, Y, and Sc) with A-type (hexagonal) and B-type (monoclinic) configurations 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 Ln2O3. With the increase of the atomic number, the ionic radii of rare-earth elements Ln and the volumes of the sesquioxides Ln2O3 reflect the so-called “lanthanide contraction”. With the increase of the Ln3+-cation radius, the bulk modulus of Ln2O3 decreases and the polymorphic structures show a degenerative tendency.

This graph shows the calculated transition pressure with respect to the transition of the Ln2O3 from its B- to A-type together with the available experimental data superimposed. The transition pressure was obtained by calculating the common tangent slope of the two fitted E–V curves based on the empirical third-order Birch–Murnaghan equation of state.Figure optionsDownload as PowerPoint slide