“…Also, the number of examples of the AA′ 3 B 4 O 12 perovskites could even be larger than the number of examples of fully ordered double A 2 BB′O 6 perovskites, even though it is generally believed that B-site ordering is more common in the latter. , The coordination environments of the A 2 A′A″B 4 O 12 perovskites suggest that they have intrinsic triple A-site ordering. However, the triple ordering by different cations has been experimentally realized just in few examples so far, in R 2 MnGa(Mn 4– x Ga x )O 12 (R = Ho and Y) solid solutions, , R 2 CuMnMn 4 O 12 (R = Dy and Y), , and Ca(Mn 0.5 Cu 0.5 )FeReO 6 . In few cases of Sm 2 MnMn(Mn 3 Ti)O 12 and RMn 3 O 6 , , the A′ and A″ sites are occupied by the same element in different oxidation states (e.g., Mn 3+ at A′ and Mn 2+ at A″).…”