Synthesis, crystal structure, and magnetic properties of the manganate La2Ca2MnO6(O2) related to the hexagonal perovskite-type structure

The compound La2Ca2MnO6(O-2) has been synthesized from La2Ca2MnO7 heated at 1123 K under high pressure (4 GPa) with KClO3 as oxygen source. The crystal structure has been refined from X-ray powder data in the Rim space group. The unit-cell parameters are a = 5.6335(2) Angstrom and c = 17.4879(8) Angstrom. Perpendicular to the c-axis, the structure is built up by the periodic stacking of two close packed [LaO3] layers separated by a layer of composition [Ca2O2] containing (O-2)(2-) peroxide ions. This oxide belongs to the family of compounds formulated as [A'O-2(2)-(delta)][A(n)B(n-1)O(3n)] for n = 2 and delta = 0. It is the first member of the series where the thickness of the perovskite slab corresponds to one [BO6] (B = Mn) octahedron. The structural relationships with La2Ca2MnO7 are discussed and the magnetic properties show that in both phases manganese is tetravalent. (C) 2003 Elsevier Science (USA). All rights reserved.