The crystal structure, magnetic and electrical properties of A-site-ordered perovskite manganites Ln
1/2Ba
1/2MnO
3 (Ln=rare earth) were investigated. In the ordered Ln
1/2Ba
1/2MnO
3 (Ln = Sm-Y), a new charge/orbital ordering pattern was found. Electron diffraction studies revealed a series of superlattice reflections with modulation vectors at q
2 = (1/2, 1/2, 1/2) as well as at q
1= (1/4, 1/4, 0) in the tetragonal setting (a
p × a
p × 2a
p, a
p being the cubic perovskite lattice parameter) . Together with the results of the resonant X-ray scattering, a model for the three-dimensional charge/orbital ordering is proposed.
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