Fizika Tverdogo Tela, 1986 Volume 28, Issue 9,Pages 2711–2716(Mi ftt580)
The mixed valency of cerium and ytterbium in the $\mathrm{RM}_{2}\mathrm{X}_{2}$ intermetallic compounds $(\mathrm{M}=\mathrm{Mn},\mathrm{Fe},\mathrm{Co},\mathrm{Ni},\mathrm{Cu};\mathrm{X}=\mathrm{Si},\mathrm{Ge})$