Abstract
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 Å, b = 8.19 Å, c = 15.47 Å) from neutron powder diffraction data. The [Mn2O5.5]∞ framework is build up of row of MnO6 octahedra and MnO5 pyramids running along a⃗. 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 c⃗, oxygen vacancies being located at the level of the La layers. The magnetic structure is original: manganese spins form ferromagnetic spin-ladders along the b⃗ axis that are antiferromagnetically coupled along the a⃗ and c⃗ axis. The HREM investigation shows the existence of 90° oriented domains and twinning phenomena.
Published Version
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