Cation ordering schemes in perovskites. From left to the right: 0D (rock salt), 1D (columnar ordering), and 2D (layered ordering) are shown for $A$-site ordering in $A A^{\prime} B_{2} \mathrm{O}_{6}$ perovskites (top) and for $B$-site ordering in $A_{2} B B^{\prime} \mathrm{O}_{6}$ perovskites (bottom).
Cation ordering schemes in perovskites. From left to the right: 0D (rock salt), 1D (columnar ordering), and 2D (layered ordering) are shown for A-site ordering in A A^{\prime} B_{2} \mathrm{O}_{6} perovskites (top) and for B-site ordering in A_{2} B B^{\prime} \mathrm{O}_{6} perovskites (bottom).