High-pressure synthesis and crystal structure analysis of NaMn2O4 with the calcium ferrite-type structure

Single crystals of a new sodium manganese oxide, NaMn2O4, were synthesized for the first time using a high-temperature and high-pressure technique. The NaMn2O4 single crystal is black, has a needle shape, and crystallizes in the orthorhombic calcium ferrite-type structure, space group Pnam with image, image, image, image, and image. The structure was determined from a single-crystal X-ray study and refined to the conventional values image and image for 1190 observed reflections. The framework structure is built up from edge-sharing chains of MnO6 octahedra that condense to form one-dimensional tunnels in which the sodium atoms are located. The Mn–O bond distance and bond valence analyses revealed the manganese valence Mn3+/Mn4+ ordering in the two “double rutile” chains of NaMn2O4.