ELECTRON-DENSITY DISTRIBUTION AND CHEMICAL BONDING OF LN(2)O(3) (LN-=-Y, TM, YB) FROM POWDER X-RAY-DIFFRACTION DATA BY THE MAXIMUM-ENTROPY METHOD

The electron density distribution maps and the effective charges on Ln atoms of Ln(2)O(3) (Ln = Y, Tm, Yb), which have a C-type rare-earth s esquioxide structure, have been determined by a combination of pattern decomposition of X-ray powder diffraction data and the maximum-entrop y method (MEM). The majority of 4f-electrons, which belong to Tm and Y b atoms, is localized in the compounds and this may be due to a strong screening by the outer 5s and 5p electrons. The overlapping of electr on clouds of Ln and O atoms on Tm2O3 and Yb2O3 decreased with increasi ng bond length. The results indicated that there was a definite differ ence in the chemical bonding between 4d-atoms (Y) and 4f-atoms (Tm, Yb ). The mean effective charges on 8b- and 24d-site metal ions were +2.8 3, +2.13 and +2.03 for Y, Tm and Yb, respectively, and therefore Y2O3 has a more ionic bonding character than Tm2O3 and Yb2O3.