Oxygen and cation ordered perovskite, Ba 2Y 2Mn 4O 11

Abstract

A three-step route has been developed for the synthesis of a new oxygen-ordered double perovskite, BaYMn 2O 5.5 or Ba 2Y 2Mn 4O 11. (i) The A-site cation ordered perovskite, BaYMn 2O 5+ δ , is first synthesized at δ≈0 by an oxygen-getter-controlled low-O 2-pressure encapsulation technique utilizing FeO as the getter for excess oxygen. (ii) The as-synthesized, oxygen-deficient BaYMn 2O 5.0 phase is then readily oxygenated to the δ≈1 level by means of 1-atm-O 2 annealing at low temperatures. (iii) By annealing this fully oxygenated BaYMn 2O 6.0 in flowing N 2 gas at moderate temperatures the new intermediate oxygen content oxide, BaYMn 2O 5.5 or Ba 2Y 2Mn 4O 11, is finally obtained. From thermogravimetric observation it is seen that the final oxygen depletion from δ≈1.0 to 0.5 occurs in a single sharp step about 600°C, implying that the oxygen stoichiometry of BaYMn 2O 5+ δ is not continuously tunable within 0.5< δ<1.0. For BaYMn 2O 5.5 synchrotron X-ray diffraction analysis reveals an orthorhombic crystal lattice and a long-range ordering of the excess oxygen atoms in the YO 0.5 layer. The magnetic behavior of BaYMn 2O 5.5 (with a ferromagnetic transition at ∼133 K) is found different from those previously reported for the known phases, BaYMn 2O 5.0 and BaYMn 2O 6.0.