ISSN:
1573-8779
Source:
Springer Online Journal Archives 1860-2000
Topics:
Chemistry and Pharmacology
Notes:
Conclusion We can compare the values obtained above and in [9] for the effective ionic charges e* for all three types of REM compound examined: fluorides, oxides, and oxide fluorides. In spite of the difference in composition, all these substances can be divided into two groups by separating the cubic (or pseudo-isotropic) crystals and the anisotropic compounds. The average values of the effective charges for each of the structural groups are given in Table 7, which also gives in parentheses the values of the ionic character of the bond, calculated according to Pauling's scheme with allowance for only the nearest homogeneous coordination sphere (for example, for CN=5 instead of 11 for the hexagonal LnF3, etc.). It can be seen from the Table that the effective charges increase on going from the oxides to the fluorides of the REM, as expected in view of the fact that the electronegativity of fluorine is greater than that of oxygen. In all cases, the increase in the values of e*, noted above, is observed on going from the anisotropic to the cubic crystals of these compounds. This last feature can be attributed to a decrease in the immediate coordination sphere around the REM atoms with change in the structure of the crystal; in this case the coordination sphere is understood to consist of the nearest ligands. Calculation of the degree of ionic character by the EN method with allowance for only the atoms situated at the shortest distances shows much better agreement with experiment than the classical calculation using the formal CN [8].
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00747005
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