Structural, magnetic, and oxygen storage properties of hexagonal Dy1-xYxMnO3+δ

Single-phase polycrystalline samples of hexagonal Dy1-xYxMnO3+delta were synthesized over the full solubility range under reducing oxygen partial pressure conditions. Rietveld refinements using neutron powder diffraction data (NPD) confirmed the persistence of the parent hexagonal P(63)cm (Space group #185) structure for all the stoichiometric (delta=0) samples. The (Mn-O) bond lengths derived from NPD data were found to be consistent with non-degenerate Mn+3 high-spin state e2 e'2 in trigonalbipyramidal coordination. Detailed thermogravimetric measurements show large reversible oxygen storage/release capabilities (within the range of oxygen content 3.0-3.3) at unusually low temperatures of 200-400 degrees C in air or oxygen atmospheres. A phase transition to a new hexagonal phase (Hexl) was observed to take place around 5-0.29 for the oxygen-loaded Dy-rich samples (x < 0.5). Analysis of x-ray and neutron diffraction data using Rietveld refinements demonstrate that the superstructure is formed by tripling the c-axis of the original P63cm unit cell. Modeling of the Hexl superstructure converged to a structural symmetry consistent with the noncentrosymmetric space group R3c (#161). In magnetization measurements, a ferrimagnetic order for DyMn03.0 was observed below 8 K. The dilution of Dy magnetism with nonmagnetic yttrium results in reducing both the transition temperature and the effective paramagnetic moment. (C) 2014 Elsevier Inc. All rights reserved.