Lattice-form-dependent orbital shape and charge disproportionation in charge- and orbital-ordered manganites

The orbital shapes and charge disproportionations at nominal Mn3+ and Mn4+ sites for the charge- and orbital-ordered phases have been studied on half-doped manganites Pr (Sr0.1 Ca0.9) 2 Mn2 O7 and Eu0.5 Ca1.5 MnO4 with double-layer and single-layer Mn-O networks, respectively, by means of x-ray structural analyses, in comparison with Pr0.5 Ca0.5 MnO3 with the pseudocubic network. In a single-layer Eu0.5 Ca1.5 MnO4 system, the (y2 - z2) / (z2 - x2) -type orbital shape is observed, while the (3 y2 - r2) / (3 x2 - r2) -type orbital shape in a pseudocubic Pr0.5 Ca0.5 MnO3 system. In a double-layer Pr (Sr0.1 Ca0.9) 2 Mn2 O7 system, the orbital shape is found to undergo a large change upon thermally induced rotation of orbital stripe. Furthermore, clear charge disproportionation is observed for the pseudocubic and double-layer systems, while it is not observed in the single-layer system. These results indicate that the orbital shape and charge disproportionation are sensitive to the dimension of Mn-O network.