Coupled Commensurate Cation and Charge Modulation in the Tunneled Structure, Na0.40(2)Mno2

Na0.40(2)MnO2 belongs to a family of mixed Mn3+ and Mn4+ porous oxides that contains both octahedral and square pyramidal Mn-o units. Neutron and synchrotron radiation studies identify the presence of both sodium ordering (T-Na approximate to 310 K) and Mn charge and orbital ordering. Below T-Na, the centrosymmetric Pbam structure adopts an (a b 4c) supercell of Pnnm symmetry that accommodates a coupled commensurate modulation down the c-axis channels of both Na position and occupancy with Mn valence.