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 RSi_2-x or RGe_2-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 (VEC_A), which should not exceed 8.3. The required value of VEC_A 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 / Crystal structure / Vacancy derivative / Structure series / Valence electron concentration