High-temperature synchrotron X-ray diffraction study of LaMn7O12

The crystal structure of the 1:3 A-site ordered perovskite LaMn7O12 with manganese atoms on both the A- and B-sites, was investigated with high-temperature in-situ synchrotron X-ray diffraction (SXRD) from room temperature up to 803 K as well as with high-resolution SXRD at room temperature. A first order structural phase transition from a body centered monoclinic I2/m   to a cubic Im3¯ structure (from a+b+c+ to a+a+a+ tilt system) occurs around Tc = 653 K as evidenced by discontinuous jumps in unit cell dimensions and differential scanning calorimetric data. The temperature dependence of the Mn–O bond distances suggests that the driving force for the transition is relaxation of the Jahn–Teller distortion and subsequent change in the tilting pattern of the MnO6 octahedra.

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