“…However, the availability of a second oxidation state results in numerous interesting physical phenomena. Mixed valences can be found (Eu 3 O 4 , 2 Sm 3 S 4 , 3 Eu 3 S 4 , 3a or EuPtP 4 ) as well as intermetallic valence fluctuation materials (e.g., CeAl 3 , 5 Yb 4 Pt 9 Ga 24 , 6 CeMo 2 Si 2 C, 7 CeRu 1−x Ni x Al, 8 Ce 2 Rh 3 Sn 5 , 9 CeCu 2 Si 2 , 10 EuCu 2 Si 2 , 10,11 YbCu 2 Si 2 10 ). A rather rare feature is a temperature or pressure dependent valence phase transition.…”