Published online by Cambridge University Press: 22 March 2016
The simple perovskite manganite Sr1-x SmxMnO3 (SSMO) has been reported to have a highly-correlatedelectronic system for e g-electrons in a Mn ion. According to the previous studies, the C-typeorbital-ordered (COO) state with the I4/mcm symmetry was found to be formed fromthe disordered-cubic (DC) state on cooling. The feature of the COO state is thatits crystal structure involves both the Jahn-Teller distortion to orbitalordering and the R 25-type rotational displacement of oxygen octahedra. Because of theinvolvement of both the distortion and the displacement, their competitionshould be expected in the formation of the COO state. However, the detailedfeatures of the competition have not been understood yet. Thus, thecrystallographic features of the COO state in SSMO have been examined by x-raypowder diffraction and transmission electron microscopy. It was found that, whenthe Sm content increased from x = 0 at roomtemperature, the DC state changed into the COO state with the tetragonalsymmetry around x = 0.13. The notable feature of theCOO state is that the state is characterized by a nanometer-scaled bandedstructure consisting of an alternating array of two tetragonal bands. Onetetragonal band consisted of the COO state involving both the Jahn-Tellerdistortion and the R 25-type rotational displacement. But, there was only the latter displacementin 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 fromthe DC state should take place via the appearance of the DT state, which mayinvolve fluctuations of the C-type orbital ordering.