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

Single-phase polycrystalline samples of hexagonal Dy1−xYxMnO3+δ 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 P63cm (Space group #185) structure for all the stoichiometric (δ=0) samples. The (Mn–O) bond lengths derived from NPD data were found to be consistent with non-degenerate Mn+3 high-spin state e“2e′2 in trigonal–bipyramidal 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 °C in air or oxygen atmospheres. A phase transition to a new hexagonal phase (Hex1) was observed to take place around δ~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 Hex1 superstructure converged to a structural symmetry consistent with the noncentrosymmetric space group R3c (#161). In magnetization measurements, a ferrimagnetic order for DyMnO3.0 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.