A New Ordered Oxygen-Deficient Manganite Perovskite:  LaBaMn₂O_5.5. Crystal and Magnetic Structure

Abstract

A new ordered oxygen-deficient perovskite, LaBaMn 2 O 5.5 , has been synthesized, using the topotactic deoxygenation of the ordered LaBaMn 2 O 6 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 [Mn 2 O 5.5 ] ∞ framework is build up of row of MnO 6 octahedra and MnO 5 pyramids running along a b. This structure is intermediate between that of the ordered LaBaMn 2 O 6 perovskite and that of LaBaMn 2 O 5 : it consists of ordered barium and lanthanum layers stacked alternatively along c b, 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 B axis that are antiferromagnetically coupled along the a b and c b axis. The HREM investigation shows the existence of 90°oriented domains and twinning phenomena.

Redox behavior of the SOFC electrode candidate NdBaMn2O5+δ investigated by high-temperature in situ neutron diffraction: first characterisation in real time of an LnBaMn2O5.5 intermediate phase

“…In the pyramid, the axial Mn1-O2 bond is elongated (9) <Ba-O> 2.96(1) 2.08 (6) <Mn1-O> 1.936 (8) 3.17 (6) <Mn2-O> 2.068(9) 2.83 (8) axis (1.939 Å) and the two axial bonds Mn2-O2 (1.972 Å) and Mn2-O5 (1.942 Å), indicating that the dz 2 orbital is along the a-axis. From these observations, we can confirm that antiferrodistortive orbital ordering is present at 800 °C in NdBaMn2O5.5 as observed at room temperature for other half-doped manganites 35,36 . Figure 16 illustrates the thermal evolution of the lattice parameters and volume of the "O5.…”

Effect of oxygen content on magnetization and magnetoresistance properties of CMR manganites

“…It is very likely the first possibility is realized as a result of the oxygen vacancies ordering. In support of this we can recall the new ordered oxygen-deficient perovskite LaBaMn 2 O 5.5 , which has been synthesized using the topotactic deoxygenation of the ordered LaBaMn 2 O 6 perovskite [29]. However, we have not any direct demonstration of the fact of oxygen ordering in our compound.…”

Oxygen and cation ordered perovskite, Ba2Y2Mn4O11

“…There the orthorhombic splitting is assumed to originate from ordering of excess oxygen atoms within the YO 0.5 layer [3]. Such ordering has recently been confirmed for orthorhombic BaLaMn 2 O 5.5 [15].…”

“…In the crystal structure, barium and yttrium takes twelve and ten coordinated sites, respectively (Table 3). There are two types of isovalent manganese atoms; bond-valence-sum calculation revealed a valence value of 3.32/3.30 for Mn1/Mn2 (Table 3) The preliminary ED data for BaYMn 2 O 5.5 [16] differ from those published for BaLaMn 2 O 5.5 [15] by showing additional spots that correspond to a repetition c = 8c p , i.e. twice the c axis now adopted.…”