Electron density distribution and chemical bonding of Ln 2O 3 (Ln = Y, Tm, Yb) from powder X-ray diffraction data by the maximum-entropy method

Abstract

The electron density distribution maps and the effective charges on Ln atoms of Ln 2O 3 (Ln = Y, Tm, Yb), which have a C-type rare-earth sesquioxide structure, have been determined by a combination of pattern decomposition of X-ray powder diffraction data and the maximum-entropy method (MEM). The majority of 4 f-electrons, which belong to Tm and Yb atoms, is localized in the compounds and this may be due to a strong screening by the outer 5 s and 5 p electrons. The overlapping of electron clouds of Ln and 0 atoms on Tm 2O 3 and Yb 2O 3 decreased with increasing bond length. The results indicated that there was a definite difference in the chemical bonding between 4 d-atoms (Y) and 4 f-atoms (Tm,Yb). The mean effective charges on 8 b- and 24 d-site metal ions were +2.83, +2.13 and +2.03 for Y, Tm and Yb, respectively, and therefore Y 2O 3 has a more ionic bonding character than Tm 2O 3 and Yb 2O 3.