Structural defects of
rare-earth disilicides and digermanides
Chem.
Met. Alloys 13 (2020)
36-44
https://doi.org/10.30970/cma13.0403
Svitlana PUKAS, Roman GLADYSHEVSKII
Based on literature
data and own experimental data the crystal structures of (defect) binary disilicides and digermanides of
rare-earth metals (R) have been
reviewed and discussed. In each of the binary systems R–{Si,Ge} up to six compounds of variable
composition RSi2-x or RGe2-x (x = 0-0.5) are known. At
certain compositions ordering of vacancies with formation of superstructures is
observed. The electronic factor has a significant impact on the formation of a
particular type of structure and it is shown that an essential criterion for
the formation of stoichiometric and off-stoichiometric disilicides (digermanides) of rare-earth metals is the valence electron
concentration per p-element atom (VECA),
which should not exceed 8.3. The required value of VECA may be
achieved by Si(Ge) vacancies, heterovalent substitution by Al or Ga
atoms, or intergrowth with other structural segments.
Structure type α-ThSi2 and
ordered vacancy derivatives.
Keywords
Rare-earth metal / Silicide / Germanide /