A new ordered oxygen-deficient manganite perovskite:: LaBaMn2O5.5.: Crystal and magnetic structure

A new ordered oxygen-deficient perovskite, LaBaMn2O5.5, has been synthesized, using the topotactic deoxygenation of the ordered LaBaMn2O6 perovskite, The crystal structure of this manganite was solved in the space group Ammm (a = 3.86 Angstrom, b = 8.19 Angstrom, c = 15.47 Angstrom) from neutron powder diffraction data. The [Mn2O5.5](infinity) framework is build up of row of MnO6 octahedra and MnO5 pyramids running along (a) over right arrow. This structure is intermediate between that of the ordered LaBaMn2O6 perovskite and that of LaBaMn2O5: it consists of ordered barium and lanthanum layers stacked alternatively along (c) over right arrow, oxygen vacancies being located at the level of the La layers. The magnetic structure is original: manganese spins form ferromagnetic spin-ladders along the b axis that are antiferromagnetically coupled along the (a) over right arrow and (c) over right arrow axis. The HREM investigation shows the existence of 90 degrees oriented domains and twinning phenomena.