We investigated the crystal structures of single-crystal Nd 0.2Sr 0.8MnO 3 by means of synchrotron x-ray diffraction measurement and transmission electron microscopy. We observed the coexistence of distinct crystal-structural phases, i.e., tetragonal (orbital ordered) and cubic (orbital disordered) phases, over a significantly wide range of temperatures. The ratio of these phases varied continuously with temperature. These indicate that the crystal exhibits a diffuse phase transition of the 3z 2 - r 2-type orbital ordering. Moreover, we observed the anisotropic evolution of the orbital-ordered nanodomains in the cubic phase. This specific nature of the phase transition probably originates from the competition between the orbital order and disorder.
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