Commensurate structural modulation in the charge- and orbitally ordered phase of the quadruple perovskite (NaMn3) Mn4 O12

By means of synchrotron x-ray and electron diffraction, we studied the structural changes at the charge order transition TCO=176 K in the mixed-valence quadruple perovskite (NaMn3)Mn4O12. Below TCO we find satellite peaks indicating a commensurate structural modulation with the same propagation vector q=(1/2,0,-1/2) of the CE magnetic structure that orders at low temperatures, similarly to the case of simple perovskites such as La0.5Ca0.5MnO3. In the present case, the modulated structure, together with the observation of a large entropy change at TCO, gives evidence of a rare case of full Mn3+/Mn4+ charge and orbital order, consistent with the Goodenough-Kanamori model.