The Seeded Photosensitive Precursor Method was successfully used for integration of lead-free BiFeO3 ferroelectric thin films with flexible plastic substrates at temperatures as low as 300 °C.
Hexagonal manganates RMnO 3 (R=Y, Ho, Dy) have been recently shown to exhibit oxygenstorage capacities promising for three-way catalysts, air-separation, and related technologies.Here, we demonstrate that Ti substitution for Mn can be used to chemically tune the oxygenbreathing properties of these materials towards practical applications. Specifically, Y(Mn 1-x Ti x )O 3 solid solutions exhibit facile oxygen absorption/desorption via reversible Ti 3+ Ti 4+ and Mn 3+ Mn 4+ reactions already in ambient air at ≈400 °C and ≈250 °C, respectively. On cooling, the oxidation of both cations is accompanied by oxygen uptake yielding a formula YMn 3+ 1-xy Mn 4+ y Ti 4+x O 3+ . The presence of Ti promotes the oxidation of Mn 3+ to Mn 4+ , which is almost negligible for YMnO 3 in air, thereby increasing the uptake of oxygen beyond that required for a given Ti 4+ concentration. The reversibility of the redox reactions is limited by sluggish kinetics; however, the oxidation process continues, if slowly, even at room temperature. The extra oxygen atoms are accommodated by the large interstices within a triangular lattice formed by the [MnO 5 ] trigonal bipyramids. According to bond distances from Rietveld refinements using the neutron diffraction data, the YMnO 3 structure features under-bonded Mn and even more severely under-bonded oxygen atoms that form the trigonal bases of the [MnO 5 ] bipyramids. The tensile bond strain around the 5-fold coordinated Mn site and the strong preference of Ti 4+ (and Mn 4+ ) for higher coordination numbers likely provide driving forces for the oxidation reaction. Reverse Monte Carlo refinements of the local atomic displacements using neutron total scattering revealed how the excess oxygen atoms are accommodated in the structure by correlated local displacements of the host atoms. Large displacements of the under-bonded host oxygen atoms play a key part in this lattice-relaxation process, facilitating reversible exchange of significant amounts of oxygen with atmosphere.
Electromagnetic fields interacting with microscopic structural features in a composite material provide emerging optical properties that surpass those offered by the individual components. However, composite materials can be generally lossy due to the scattering effects induced by inhomogeneities at the interfaces between different compounds. To overcome such problems, complicated and costly manufacturing procedures, such as top‐down approaches, are generally required. In contrast, here ZnO–ZnWO4 eutectic self‐organized composites grown by the micropulling method are considered, displaying sharp and strongly polarized transmission at 397 nm. Such an optical response is notable because it is not observed in either ZnO or ZnWO4 single crystals. The optical response is due to the refractive index matching of the two constituents, which self‐organize into ordered structures via a micropulling down method. The optical behavior reported here can directly lead to applications, such as tunable narrowband filters with bandpass of 3 nm and polarizers, paving the way to a new self‐organization route for manufacturing optical components.
The temperature dependence of the dielectric properties and ac conduction of YMnO3 ceramics annealed under different atmospheres is investigated from 25 to 700 °C. The origin of the dielectric anomalies is clarified. Two dielectric peaks in the permittivity accompanied by a single anomaly in the dielectric losses characterize the dielectric response. Simultaneously, three different regions can be distinguished in the temperature dependence of ac conductivity. Oxygen vacancies with an activation energy for the conduction of 1.13 eV are suggested to be responsible for the dielectric anomaly observed at < 400 °C. For temperatures > 400 °C, the dielectric data are influenced by conductivity and no ferroelectric anomaly is obvious.
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