Characterization of Oxygen Storage and Structural Properties of Oxygen-Loaded Hexagonal RMnO3+δ (R = Ho, Er, and Y)
Characterization of Oxygen Storage and Structural Properties of Oxygen-Loaded Hexagonal RMnO3+δ (R = Ho, Er, and Y)
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DOI：
10.1021/acs.chemmater.5b01817
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发表时间：
2015-09-22
影响因子：
8.6
通讯作者：
Chmaissem, O.
中科院分区：
文献类型：
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作者：
Abughayada, C.;Dabrowski, B.;Chmaissem, O.
化学计量比RMnO_3+Delta(R=Er，Y和Ho)的单相多晶样品是在六方P6(3)cm结构中通过类似于1300℃的固相反应获得的。氧气气氛中的热重测量表明，在类似于190-325℃的异常低温范围内，具有较大Ho和Y的样品表现出快速和可逆的大量过剩氧(0.3>；Delta>；0)的结合，这表明RMnO+Delta材料可用于低成本的热摆动吸附过程以从空气中分离氧气。在高压氧条件下退火后，所有材料的增量氧摄入量都进一步增加，接近0.38。热重测量、同步加速器X射线和中子衍射证实了6=0、0.28和0.38的三个氧稳定相的形成。原位同步加速器衍射证明了这些单相及其产生和共存的区域的热稳定性，并证明了δ=0.28相的稳定性随R离子离子尺寸的增大而增加。利用氧过剩相的中子粉末衍射结构模拟描述了通过将原始母体晶胞的c轴增加三倍而观察到的HoMnO3.28的大型R3c超结构的形成和细节。对RMnO_(3.38)(R=Y和Er)载氧相的模拟收敛到与PCa2(1)对称性一致的结构模型上。
Single-phase polycrystalline samples of stoichiometric RMnO3+delta (R = Er, Y, and Ho) were achieved in the hexagonal P6(3)cm structure through solid state reaction at, similar to 1300 degrees C. Thermogravimetric measurements in oxygen atmospheres demonstrated that samples with the larger Ho and Y show rapid and reversible incorporation of large amounts of excess oxygen (0.3 > delta> 0) at an unusually low temperature range of similar to 190-325 degrees C, indicating the industrial usefulness of RMnO3+delta materials for lower cost thermal swing adsorption processes for oxygen separation from air. Further increase of the excess oxygen intake to delta similar to 0.38 was achieved for all the investigated materials when annealed under high pressures of oxygen. The formation of three oxygen stable phases with 6 = 0, 0.28, and 0.38 was confirmed by thermogravimetric measurements, synchrotron X-rays, and neutron diffraction. In situ synchrotron diffraction proved the thermal stability of these single phases and the regions of their creation and coexistence, and demonstrated that the stability of the delta = 0.28 phase increases with the ionic size of the R ion. Structural modeling using neutron powder diffraction for oxygen excess phases describes the formation and details of a large R3c superstructure observed for HoMnO3.28 by tripling the c-axis of the original parent unit cell. Modeling of the RMnO3.38 (R = Y and Er) oxygen-loaded phase converged on a structural model consistent with the symmetry of Pca2(1).