The simple perovskite manganite Sr1-xSmxMnO3 (SSMO) has been reported to have a highly-correlated
electronic system for eg-electrons in a Mn ion. According to the previous studies, the C-type
orbital-ordered (COO) state with the I4/mcm symmetry was found to be formed from
the disordered-cubic (DC) state on cooling. The feature of the COO state is that
its crystal structure involves both the Jahn-Teller distortion to orbital
ordering and the R25-type rotational displacement of oxygen octahedra. Because of the
involvement of both the distortion and the displacement, their competition
should be expected in the formation of the COO state. However, the detailed
features of the competition have not been understood yet. Thus, the
crystallographic features of the COO state in SSMO have been examined by x-ray
powder diffraction and transmission electron microscopy. It was found that, when
the Sm content increased from x = 0 at room
temperature, the DC state changed into the COO state with the tetragonal
symmetry around x = 0.13. The notable feature of the
COO state is that the state is characterized by a nanometer-scaled banded
structure consisting of an alternating array of two tetragonal bands. One
tetragonal band consisted of the COO state involving both the Jahn-Teller
distortion and the R25-type rotational displacement. But, there was only the latter displacement
in the other, the state of which could be identified as a disordered tetragonal
(DT) state. Based on this, it is understood that the COO-state formation from
the DC state should take place via the appearance of the DT state, which may
involve fluctuations of the C-type orbital ordering.