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The checkerboard pattern of Bi0.63Sr0.37MnO3 determined using resonant x-ray scattering at the Mn K edge

A study using resonant x-ray scattering at the Mn K edge has been carried out on a Bi0.63Sr0.37MnO3 single crystal. This compound undergoes a metal–insulator phase transition to the so-called charge ordered (CO) state at about 530 K. Strong resonance signals were observed at room temperature as the energy was tuned through the Mn K edge for several superstructures of the CO phase. The energy, polarization and azimuth angle dependences agree with a checkerboard ordering in the ab plane of manganese atoms of two types, in terms of their different local geometrical structures. One of the sites is anisotropic—a tetragonal distorted oxygen octahedron—and the other is isotropic—a nearly undistorted one, as observed for Bi0.5Sr0.5MnO3 and other half-doped manganites. This result indicates that the checkerboard pattern is strongly stable and extends to doping concentrations x<0.5. No superstructures corresponding to the doubling of the c axis were detected. Intermediate valence states lower than 3.5, according to the fractional charge segregation, were deduced for the two non-equivalent Mn atoms, i.e. Mn3.30+ and Mn3.44+.